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Mar 05, 2023

51 min #nix · #rust

Generating a docker image with nix

From the series Building a Rust service with Nix

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There it is. The final installment.

Over the course of this series, we've built a very useful Rust web service that shows us colored ASCII art cats, and we've packaged it with docker, and deployed it to https://fly.io.

We did all that without using nix at all, and then in the last few chapters, we've learned to use nix, and now it's time to tell docker build goodbye, along with this whole-ass Dockerfile:

# syntax = docker/dockerfile:1.4

################################################################################
FROM ubuntu:20.04 AS base

################################################################################
FROM base AS builder

# Install compile-time dependencies
RUN set -eux; \
		apt update; \
		apt install -y --no-install-recommends \
			# 👇 new!
			openssh-client git-core curl ca-certificates gcc libc6-dev pkg-config libssl-dev \
			;

# Install rustup
RUN set -eux; \
		curl --location --fail \
			"https://static.rust-lang.org/rustup/dist/x86_64-unknown-linux-gnu/rustup-init" \
			--output rustup-init; \
		chmod +x rustup-init; \
		./rustup-init -y --no-modify-path --default-toolchain stable; \
		rm rustup-init;

# Add rustup to path, check that it works
ENV PATH=${PATH}:/root/.cargo/bin
RUN set -eux; \
		rustup --version;

# Copy sources and build them
WORKDIR /app
COPY src src
COPY .cargo .cargo
COPY Cargo.toml Cargo.lock rust-toolchain.toml ./
RUN mkdir -p ~/.ssh/ && ssh-keyscan ssh.shipyard.rs >> ~/.ssh/known_hosts
RUN --mount=type=cache,target=/root/.rustup \
    --mount=type=cache,target=/root/.cargo/registry \
    --mount=type=cache,target=/root/.cargo/git \
		--mount=type=cache,target=/app/target \
		--mount=type=ssh \
		# 👇 new!
		--mount=type=secret,id=shipyard-token \
		set -eux; \
		export CARGO_REGISTRIES_CATSCII_TOKEN=$(cat /run/secrets/shipyard-token); \
		rustc --version; \
		cargo build --release; \
		objcopy --compress-debug-sections ./target/release/catscii ./catscii

################################################################################
FROM base AS app

SHELL ["/bin/bash", "-c"]

# Install run-time dependencies, remove extra APT files afterwards.
# This must be done in the same `RUN` command, otherwise it doesn't help
# to reduce the image size.
RUN set -eux; \
		apt update; \
		apt install -y --no-install-recommends \
			ca-certificates \
			; \
		apt clean autoclean; \
		apt autoremove --yes; \
		# Note: 👇 this only works because of the `SHELL` instruction above.
		rm -rf /var/lib/{apt,dpkg,cache,log}/

# Copy app from builder
WORKDIR /app
COPY --from=builder /app/catscii .

# Copy Geolite2 database
RUN mkdir /db
COPY ./db/GeoLite2-Country.mmdb /db/

CMD ["/app/catscii"]

So, let's begin with:

$ git rm --force Dockerfile
rm 'Dockerfile'
$ git commit --message "Ahhhh."
[main ab28bcd] Ahhhh.
 1 file changed, 76 deletions(-)
 delete mode 100644 Dockerfile

And let out a sigh of relief.

Building catscii with `nix build`

Before we need to be able to build a Docker image, we need to be able to build an executable.

Remember when we learned nix, how we were able to do nix build? Well it's time to do that for catscii.

But luckily, we've set up everything we need, and so it'll be painless.

We'll use the crane nix library to build it.

The plan is to:

add it as an input
call one of its functions
assign that to something under packages in our flake output

Good? Good.

Let's start by adding it:

󱄅# in `flake.nix`
{
  inputs = {
    crane = {
      url = "github:ipetkov/crane";
    };
	# omitted: other inputs
  }
  # new: `crane` is in that list now 👇
  outputs = { self, nixpkgs, flake-utils, rust-overlay, crane }:
	# omitted: body of `outputs`
}

Before we go any further, vibe check:

$ nix flake metadata
warning: Git tree '/home/amos/catscii' is dirty
warning: updating lock file '/home/amos/catscii/flake.lock':
• Added input 'crane':
    'github:ipetkov/crane/34633dd0d7ff2226627647cf44a5a197ca652c7d' (2023-02-19)
• Added input 'crane/flake-compat':
    'github:edolstra/flake-compat/35bb57c0c8d8b62bbfd284272c928ceb64ddbde9' (2023-01-17)
• Added input 'crane/flake-utils':
    'github:numtide/flake-utils/3db36a8b464d0c4532ba1c7dda728f4576d6d073' (2023-02-13)
• Added input 'crane/nixpkgs':
    'github:NixOS/nixpkgs/6d33e5e14fd12f99ba621683ae90cebadda753ca' (2023-02-15)
• Added input 'crane/rust-overlay':
    'github:oxalica/rust-overlay/a619538647bd03e3ee1d7b947f7c11ff289b376e' (2023-02-15)
• Added input 'crane/rust-overlay/flake-utils':
    follows 'crane/flake-utils'
• Added input 'crane/rust-overlay/nixpkgs':
    follows 'crane/nixpkgs'
warning: Git tree '/home/amos/catscii' is dirty
Resolved URL:  git+file:///home/amos/catscii
Locked URL:    git+file:///home/amos/catscii
Path:          /nix/store/11p3avrd17fr78fl8qz05x1jjfn0dd6f-source
Last modified: 2023-02-19 19:19:54
Inputs:
├───crane: github:ipetkov/crane/34633dd0d7ff2226627647cf44a5a197ca652c7d
│   ├───flake-compat: github:edolstra/flake-compat/35bb57c0c8d8b62bbfd284272c928ceb64ddbde9
│   ├───flake-utils: github:numtide/flake-utils/3db36a8b464d0c4532ba1c7dda728f4576d6d073
│   ├───nixpkgs: github:NixOS/nixpkgs/6d33e5e14fd12f99ba621683ae90cebadda753ca
│   └───rust-overlay: github:oxalica/rust-overlay/a619538647bd03e3ee1d7b947f7c11ff289b376e
│       ├───flake-utils follows input 'crane/flake-utils'
│       └───nixpkgs follows input 'crane/nixpkgs'
├───flake-utils: github:numtide/flake-utils/3db36a8b464d0c4532ba1c7dda728f4576d6d073
├───nixpkgs: github:NixOS/nixpkgs/28319deb5ab05458d9cd5c7d99e1a24ec2e8fc4b
└───rust-overlay: github:oxalica/rust-overlay/3bab7ae4a80de02377005d611dc4b0a13082aa7c
    ├───flake-utils follows input 'flake-utils'
    └───nixpkgs follows input 'nixpkgs'

Okay! crane depends on nixpkgs, rust-overlay, and flake-utils, which we already have, so, let's deduplicate those:

󱄅	# in inputs
    crane = {
      url = "github:ipetkov/crane";
      inputs = {
        nixpkgs.follows = "nixpkgs";
        rust-overlay.follows = "rust-overlay";
        flake-utils.follows = "flake-utils";
      };
    };

$ nix flake metadata
warning: Git tree '/home/amos/catscii' is dirty
Resolved URL:  git+file:///home/amos/catscii
Locked URL:    git+file:///home/amos/catscii
Path:          /nix/store/k5rvn7vp6pfhk291r55r8g2ga7w7546w-source
Last modified: 2023-02-19 19:19:54
Inputs:
├───crane: github:ipetkov/crane/34633dd0d7ff2226627647cf44a5a197ca652c7d
│   ├───flake-compat: github:edolstra/flake-compat/35bb57c0c8d8b62bbfd284272c928ceb64ddbde9
│   ├───flake-utils follows input 'flake-utils'
│   ├───nixpkgs follows input 'nixpkgs'
│   └───rust-overlay follows input 'rust-overlay'
├───flake-utils: github:numtide/flake-utils/3db36a8b464d0c4532ba1c7dda728f4576d6d073
├───nixpkgs: github:NixOS/nixpkgs/28319deb5ab05458d9cd5c7d99e1a24ec2e8fc4b
└───rust-overlay: github:oxalica/rust-overlay/3bab7ae4a80de02377005d611dc4b0a13082aa7c
    ├───flake-utils follows input 'flake-utils'
    └───nixpkgs follows input 'nixpkgs'

Alright! That's better.

Let's keep going:

󱄅# in flake.nix
{
  inputs = {
    # cut
  };
  outputs = { self, nixpkgs, flake-utils, rust-overlay, crane }:
    flake-utils.lib.eachDefaultSystem
      (system:
        let
          overlays = [ (import rust-overlay) ];
          pkgs = import nixpkgs {
            inherit system overlays;
          };
          rustToolchain = pkgs.pkgsBuildHost.rust-bin.fromRustupToolchainFile ./rust-toolchain.toml;
          # this is how we can tell crane to use our toolchain!
          craneLib = (crane.mkLib pkgs).overrideToolchain rustToolchain;
          # cf. https://crane.dev/API.html#libcleancargosource
          src = craneLib.cleanCargoSource ./.;
          # as before
          nativeBuildInputs = with pkgs; [ rustToolchain pkg-config ];
          buildInputs = with pkgs; [ openssl sqlite ];
          # because we'll use it for both `cargoArtifacts` and `bin`
          commonArgs = {
            inherit src buildInputs nativeBuildInputs;
          };
          cargoArtifacts = craneLib.buildDepsOnly commonArgs;
          # remember, `set1 // set2` does a shallow merge:
          bin = craneLib.buildPackage (commonArgs // {
            inherit cargoArtifacts;
          });
        in
        with pkgs;
        {
          packages =
            {
              # that way we can build `bin` specifically,
              # but it's also the default.
              inherit bin;
              default = bin;
            };
          devShells.default = mkShell {
            # instead of passing `buildInputs` / `nativeBuildInputs`,
            # we refer to an existing derivation here
            inputsFrom = [ bin ];
          };
        }
      );
}

And that's it! We're good to go!

$ nix build
warning: Git tree '/home/amos/catscii' is dirty
error: not sure how to download crates from registry+ssh://git@ssh.shipyard.rs/catscii/crate-index.git.
       for example, this can be resolved with:

       craneLib = crane.lib.${system}.appendCrateRegistries [
         (lib.registryFromDownloadUrl {
           dl = "https://crates.io/api/v1/crates";
           indexUrl = "https://github.com/rust-lang/crates.io-index";
         })

         # Or, alternatively
         (lib.registryFromGitIndex {
           url = "https://github.com/Hirevo/alexandrie-index";
           rev = "90df25daf291d402d1ded8c32c23d5e1498c6725";
         })
       ];

       # Then use the new craneLib instance as you would normally
       craneLib.buildPackage {
         # ...
       }
(use '--show-trace' to show detailed location information)

Oh, um. Almost. We do have a private registry in there, which I did on purpose, specifically to show how we could solve that problem with Docker and with crane.

Because we already have a secrets/shipyard-token file (protected by git-crypt), it's actually fairly easy to get out of. Crane even has a whole docs page about it.

Replace the craneLib = line with these:

󱄅craneLibWithoutRegistry = (crane.mkLib pkgs).overrideToolchain rustToolchain;
shipyardToken = builtins.readFile ./secrets/shipyard-token;
craneLib = craneLibWithoutRegistry.appendCrateRegistries [
	(craneLibWithoutRegistry.registryFromDownloadUrl {
		dl = "https://crates.shipyard.rs/api/v1/crates";
		indexUrl = "ssh://git@ssh.shipyard.rs/catscii/crate-index.git";
		fetchurlExtraArgs = {
			curlOptsList = [ "-H" "user-agent: shipyard ${shipyardToken}" ];
		};
	})
];

And this time, we're actually good to go!

Cool bear's hot tip

If this seems like a terrible no-good workaround until some standard is decided and implemented everywhere, that's because it is!

You can check the tracking issue to see where the discussion is at by the time you actually read this.

Anyway, with that, nix build actually does work:

$ nix build
(cut)

And in result, we have our binary!

$ ls --long --header --almost-all result
lrwxrwxrwx 1 amos amos 57 Feb 19 19:47 result -> /nix/store/dvfh98mvqish3jsih29rs3r45qn3yfpf-catscii-0.1.0

$ tree -ah result
[  57]  result
└── [4.0K]  bin
    └── [8.7M]  catscii

1 directory, 1 file

Which only depends on things provided by nix:

$ ldd ./result/bin/catscii
        linux-vdso.so.1 (0x00007ffd31d2b000)
        libssl.so.3 => /nix/store/dsf1m9azqqz6c3nqj9yk0nnardqmaia0-openssl-3.0.8/lib/libssl.so.3 (0x00007f7fb1362000)
        libcrypto.so.3 => /nix/store/dsf1m9azqqz6c3nqj9yk0nnardqmaia0-openssl-3.0.8/lib/libcrypto.so.3 (0x00007f7fb0600000)
        libsqlite3.so.0 => /nix/store/zqf9r5d9yv4ccv64ja8xjn8kasgqg3cy-sqlite-3.40.1/lib/libsqlite3.so.0 (0x00007f7fb0ab1000)
        libgcc_s.so.1 => /nix/store/lqz6hmd86viw83f9qll2ip87jhb7p1ah-glibc-2.35-224/lib/libgcc_s.so.1 (0x00007f7fb1348000)
        libm.so.6 => /nix/store/lqz6hmd86viw83f9qll2ip87jhb7p1ah-glibc-2.35-224/lib/libm.so.6 (0x00007f7fb0520000)
        libc.so.6 => /nix/store/lqz6hmd86viw83f9qll2ip87jhb7p1ah-glibc-2.35-224/lib/libc.so.6 (0x00007f7fb0200000)
        libdl.so.2 => /nix/store/lqz6hmd86viw83f9qll2ip87jhb7p1ah-glibc-2.35-224/lib/libdl.so.2 (0x00007f7fb1341000)
        libpthread.so.0 => /nix/store/lqz6hmd86viw83f9qll2ip87jhb7p1ah-glibc-2.35-224/lib/libpthread.so.0 (0x00007f7fb133c000)
        libz.so.1 => /nix/store/9dz5lmff9ywas225g6cpn34s0wbldnxa-zlib-1.2.13/lib/libz.so.1 (0x00007f7fb131e000)
        /nix/store/lqz6hmd86viw83f9qll2ip87jhb7p1ah-glibc-2.35-224/lib/ld-linux-x86-64.so.2 => /nix/store/lqz6hmd86viw83f9qll2ip87jhb7p1ah-glibc-2.35-224/lib64/ld-linux-x86-64.so.2 (0x00007f7fb1411000)

And runs fine!

$ ./result/bin/catscii
{"timestamp":"2023-02-19T18:49:06.782034Z","level":"INFO","fields":{"message":"Creating honey client","log.target":"libhoney::client","log.module_path":"libhoney::client","log.file":"/nix/store/eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee-vendor-cargo-deps/2b916d13eeef5c4c978dd7cdbe0195cb3a2cb3e77889acf9f85433ddf74a8e14/libhoney-rust-0.1.6/src/client.rs","log.line":78},"target":"libhoney::client"}
{"timestamp":"2023-02-19T18:49:06.782112Z","level":"INFO","fields":{"message":"transmission starting","log.target":"libhoney::transmission","log.module_path":"libhoney::transmission","log.file":"/nix/store/eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee-vendor-cargo-deps/2b916d13eeef5c4c978dd7cdbe0195cb3a2cb3e77889acf9f85433ddf74a8e14/libhoney-rust-0.1.6/src/transmission.rs","log.line":124},"target":"libhoney::transmission"}
{"timestamp":"2023-02-19T18:49:06.812601Z","level":"INFO","fields":{"message":"Listening on 0.0.0.0:8080"},"target":"catscii"}
^C{"timestamp":"2023-02-19T18:49:11.819055Z","level":"WARN","fields":{"message":"Initiating graceful shutdown"},"target":"catscii"}

Generating a docker image

Here it is! The last thing we have to do.

nix comes with facilities to generate Docker images, which we should really call OCI images, without using Docker at all: those images are, after all, "just" tarballs with a well-known structure and some JSON manifests.

Let's first try to make a docker image with just our binary: we know it won't be enough, since we need to have the geo-ip database in there, but it's a start.

In our outputs' let block, next to bin, we can define a new key:

󱄅# in flake.nix
{
  inputs = {
    # cut
  };
  outputs = { self, nixpkgs, flake-utils, rust-overlay, crane }:
    flake-utils.lib.eachDefaultSystem
      (system:
        let
          # omitted: most keys
          bin = craneLib.buildPackage (commonArgs // {
            inherit cargoArtifacts;
          });
          # new! 👇
          dockerImage = pkgs.dockerTools.buildImage {
            name = "catscii";
            tag = "latest";
            copyToRoot = [ bin ];
            config = {
              Cmd = [ "${bin}/bin/catscii" ];
            };
          };
        in
        with pkgs;
        {
          packages =
            {
              # new package: 👇
              inherit bin dockerImage;
              default = bin;
            };
          devShells.default = mkShell {
            inputsFrom = [ bin ];
          };
        }
      );
}

Let's try building it and see what we got in there!

$ nix build .#dockerImage
warning: Git tree '/home/amos/catscii' is dirty

Huh, that was quick!

Yeah! The bin target was already built, and since everything is content-addressed, and none of the inputs changed, it really did just generate the Docker image from that.

Let's see what the result file is now:

$ file result
result: symbolic link to /nix/store/c8g0an3rabk3i0zivrxcpnivkmy15sq5-docker-image-catscii.tar.gz

A symbolic link to a tarball. We can load this into our local docker registry with docker load:

$ docker load < result
Command 'docker' not found, but can be installed with:
sudo snap install docker         # version 20.10.17, or
sudo apt  install docker.io      # version 20.10.16-0ubuntu1
sudo apt  install podman-docker  # version 3.4.4+ds1-1ubuntu1
See 'snap info docker' for additional versions.

...ah, we haven't installed docker yet! If you needed proof that nix truly can build docker image without docker, I guess this is it.

In a real-world scenario, I'd probably want to have docker installed locally to be able to run the image, but for now let's look at it another way: with the dive utility.

Let's add it to our dev shell:

󱄅devShells.default = mkShell
  {
    inputsFrom = [ bin ];
    # new!                      👇
    buildInputs = with pkgs; [ dive ];
  };

For some reason, pressing Enter didn't do the trick for me this time, I had to close the shell and open a new one.

Now, dive generally takes a name:tag reference, which goes into the local Docker registry. But we don't have Docker! It also supports the docker-archive:// protocol, but that requires .tar files, whereas we have a .tar.gz file.

So, let's gunzip it first:

$ gunzip --stdout result > /tmp/image.tar && dive docker-archive:///tmp/image.tar
Image Source: docker-archive:///tmp/image.tar
Fetching image... (this can take a while for large images)
Analyzing image...
Building cache...

And we're presented with a TUI (text-user interface), which we've actually already used in Part 6:

dive's TUI interface. The main points are described below.

Wait... it's only 58MB?

Yes it is! Remember how we struggled to get it below 100MB when we wrote the Dockerfile by hand? Well, here's our first try, and it's almost half.

There's still a couple things missing from there, but nothing too big.

Note that we could've tried harder with the Dockerfile: the base Ubuntu system takes some space, we could've used a distroless image as a base - they even have an example for Rust!

But we would have to figure out how to ship sqlite, for example. I'm sure there's a way, I just... I'm just not sure why I'd bother, since nix lets us solve both the "build a binary that can run anywhere" and "generate a small docker image while we're at it".

Running our app locally with Docker

Before we deploy it to production, let's make sure it runs locally, which is one of the big selling points of Docker.

Digression: a dev shell docker?

Installing the latest Docker on Ubuntu was a bit of a hassle last time.

Can we just add docker to our dev shell and see if it works?

Out of curiosity, I tried that. First off, it's not a small download (half a gig). Secondly, when you install Docker via Ubuntu packages, it does a couple things, like set up a systemd service to start the docker daemon, and set up user groups.

Without that, we have to start the daemon ourselves, and it's more subtle than you'd think.

The daemon does need to run, so docker info doesn't work out of the box:

$ docker info
Client:
 Context:    default
 Debug Mode: false
 Plugins:
  buildx: Docker Buildx (Docker Inc., v0.9.1)
  compose: Docker Compose (Docker Inc., 2.15.1)

Server:
ERROR: Cannot connect to the Docker daemon at unix:///var/run/docker.sock. Is the docker daemon running?
errors pretty printing info

Starting the docker daemon as an unprivileged user is possible in theory, it's called "rootless mode", but it's not the default, so just running "dockerd" doesn't work:

$ dockerd
INFO[2023-02-21T14:12:51.135602597+01:00] Starting up
dockerd needs to be started with root privileges. To run dockerd in rootless mode as an unprivileged user, see https://docs.docker.com/go/rootless/

There's a dockerd-rootless executable in $PATH, but it ends up failing to find newuidmap.

$ dockerd-rootless
(cut)
+ exec rootlesskit --net=slirp4netns --mtu=65520 --slirp4netns-sandbox=auto --slirp4netns-seccomp=auto --disable-host-loopback --port-driver=builtin --copy-up=/etc --copy-up=/run --propagation=rslave /nix/store/g57cgil5aznzdnkimd8g3zq3avpfdlfv-moby-20.10.23/libexec/docker/dockerd-rootless.sh
[rootlesskit:parent] error: failed to setup UID/GID map: newuidmap 73837 [0 1000 1 1 100000 65536] failed: : exec: "newuidmap": executable file not found in $PATH

That executable is in nixpkgs#shadow, but adding it doesn't work any better:

$ dockerd-rootless
(cut)
+ exec rootlesskit --net=slirp4netns --mtu=65520 --slirp4netns-sandbox=auto --slirp4netns-seccomp=auto --disable-host-loopback --port-driver=builtin --copy-up=/etc --copy-up=/run --propagation=rslave /nix/store/g57cgil5aznzdnkimd8g3zq3avpfdlfv-moby-20.10.23/libexec/docker/dockerd-rootless.sh
[rootlesskit:parent] error: failed to setup UID/GID map: newuidmap 86183 [0 1000 1 1 100000 65536] failed: newuidmap: write to uid_map failed: Operation not permitted

I suppose this all works swimmingly on NixOS, but it's a bit more delicate intruding into another distribution like that.

Anyway, we can run dockerd as root:

$ sudo dockerd
sudo: dockerd: command not found

Well, not like that - sudo sanitizes the environment, at least on Ubuntu. You can configure that, but let's not:

$ sudo $(which dockerd)
(cut: lots of INFO lines)
INFO[2023-02-21T14:20:30.740944094+01:00] API listen on /var/run/docker.sock

Now, the docker daemon is running, but a non-root user cannot talk to it:

$ docker info
Client:
 Context:    default
 Debug Mode: false
 Plugins:
  buildx: Docker Buildx (Docker Inc., v0.9.1)
  compose: Docker Compose (Docker Inc., 2.15.1)

Server:
ERROR: Got permission denied while trying to connect to the Docker daemon socket at unix:///var/run/docker.sock: Get "http://%2Fvar%2Frun%2Fdocker.sock/v1.24/info": dial unix /var/run/docker.sock: connect: permission denied

As root though, we can!

$ sudo $(which docker) info
/nix/store/561wgc73s0x1250hrgp7jm22hhv7yfln-bash-5.2-p15/bin/bash: warning: setlocale: LC_ALL: cannot change locale (en_US.UTF-8)
Client:
 Context:    default
 Debug Mode: false
 Plugins:
  buildx: Docker Buildx (Docker Inc., v0.9.1)
  compose: Docker Compose (Docker Inc., 2.15.1)

Server:
 Containers: 0
  Running: 0
  Paused: 0
  Stopped: 0
 Images: 0
 Server Version: 20.10.23
 (cut: tons of other info)

Violently chown-ing /var/run/docker.sock is an option, although not a great one:

$ sudo chown --recursive amos:amos /var/run/docker.sock

$ docker run hello-world
Unable to find image 'hello-world:latest' locally
latest: Pulling from library/hello-world
2db29710123e: Pull complete
Digest: sha256:6e8b6f026e0b9c419ea0fd02d3905dd0952ad1feea67543f525c73a0a790fefb
Status: Downloaded newer image for hello-world:latest
/nix/store/561wgc73s0x1250hrgp7jm22hhv7yfln-bash-5.2-p15/bin/bash: warning: setlocale: LC_ALL: cannot change locale (en_US.UTF-8)

Hello from Docker!
This message shows that your installation appears to be working correctly.

To generate this message, Docker took the following steps:
 1. The Docker client contacted the Docker daemon.
 2. The Docker daemon pulled the "hello-world" image from the Docker Hub.
    (amd64)
 3. The Docker daemon created a new container from that image which runs the
    executable that produces the output you are currently reading.
 4. The Docker daemon streamed that output to the Docker client, which sent it
    to your terminal.

To try something more ambitious, you can run an Ubuntu container with:
 $ docker run -it ubuntu bash

Share images, automate workflows, and more with a free Docker ID:
 https://hub.docker.com/

For more examples and ideas, visit:
 https://docs.docker.com/get-started/

Really, you're probably better off installing Docker from Ubuntu packages. But if you really wanted to have docker in your dev shell, this is how you could do it.

Loading the image into the local docker registry

So, as promised, we can load our built image into the local docker registry with docker load:

$ docker load < result
77128d0a21af: Loading layer [==================================================>]  59.17MB/59.17MB
Loaded image: catscii:latest

And then we can try to run it!

$ docker run --rm --publish 8080:8080 catscii:latest
/nix/store/561wgc73s0x1250hrgp7jm22hhv7yfln-bash-5.2-p15/bin/bash: warning: setlocale: LC_ALL: cannot change locale (en_US.UTF-8)
thread 'main' panicked at '$SENTRY_DSN must be set: NotPresent', src/main.rs:40:37
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

Ah yes! We must set a few environment variables.

If we had to do this a lot, a neat way to do it would be to:

Split those environment variables from .envrc into .env
Use the dotenv instruction to load the .env from the .envrc
Pass --env-file to docker run, or set up a docker-compose file

But for now, let's juse use -env (-e) to pass a few environment variables by hand:

$ docker run --rm --env SENTRY_DSN --env HONEYCOMB_API_KEY --env GEOLITE2_COUNTRY_DB --env ANALYTICS_DB --publish 8080:8080 catscii:latest
/nix/store/561wgc73s0x1250hrgp7jm22hhv7yfln-bash-5.2-p15/bin/bash: warning: setlocale: LC_ALL: cannot change locale (en_US.UTF-8)
{"timestamp":"2023-02-21T13:31:04.480284Z","level":"INFO","fields":{"message":"Creating honey client","log.target":"libhoney::client","log.module_path":"libhoney::client","log.file":"/nix/store/eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee-vendor-cargo-deps/2b916d13eeef5c4c978dd7cdbe0195cb3a2cb3e77889acf9f85433ddf74a8e14/libhoney-rust-0.1.6/src/client.rs","log.line":78},"target":"libhoney::client"}
{"timestamp":"2023-02-21T13:31:04.480386Z","level":"INFO","fields":{"message":"transmission starting","log.target":"libhoney::transmission","log.module_path":"libhoney::transmission","log.file":"/nix/store/eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee-vendor-cargo-deps/2b916d13eeef5c4c978dd7cdbe0195cb3a2cb3e77889acf9f85433ddf74a8e14/libhoney-rust-0.1.6/src/transmission.rs","log.line":124},"target":"libhoney::transmission"}
thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: MaxMindDb(IoError("No such file or directory (os error 2)"))', src/main.rs:59:75
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

Ah, containerization in action: it can't read the geoip country database because... it's stuck in its little container, and db/GeoLite2-Country.mmdb is outside of it.

We need a tiny bit more nix to fix this.

Shipping the geoip database

So, we already have the geoip database locally, so we can just copy it from the nix flake.

Mhh before we do that though - surely someone has already packaged that database into nixpkgs, right?

Ehhh I don't know if the license terms permit th- oh would you look at that, there it is, as clash-geoip.

Well, I suppose we can try!

󱄅dockerImage = pkgs.dockerTools.buildImage {
  name = "catscii";
  tag = "latest";
  copyToRoot = [ bin ];
  config = {
    Cmd = [ "${bin}/bin/catscii" ];
    # new 👇
    Env = with pkgs; [ "GEOLITE2_COUNTRY_DB=${clash-geoip}/etc/clash/Country.mmdb" ];
  };
};

If the casing of Cmd and Env seem weirdly out-of-place, it's because they map to the JSON format expected by the Docker Engine API, and Docker is written in Go, where public fields are UpperCamelCase.

Nice bit of trivia there but, wait, we can refer to any package? Just like that?

I'm doing what instinctively feels right!

Let's see if it actually works:

$ nix build .#dockerImage
warning: Git tree '/home/amos/catscii' is dirty
error: Package ‘clash-geoip-20230112’ in /nix/store/d5hx18py56yr4r1qzsx83q3idwxn6b19-source/pkgs/data/misc/clash-geoip/default.nix:26 has an unfree license (‘unfree’), refusing to evaluate.

       a) To temporarily allow unfree packages, you can use an environment variable
          for a single invocation of the nix tools.

            $ export NIXPKGS_ALLOW_UNFREE=1

        Note: For `nix shell`, `nix build`, `nix develop` or any other Nix 2.4+
        (Flake) command, `--impure` must be passed in order to read this
        environment variable.

       b) For `nixos-rebuild` you can set
         { nixpkgs.config.allowUnfree = true; }
       in configuration.nix to override this.

       Alternatively you can configure a predicate to allow specific packages:
         { nixpkgs.config.allowUnfreePredicate = pkg: builtins.elem (lib.getName pkg) [
             "clash-geoip"
           ];
         }

       c) For `nix-env`, `nix-build`, `nix-shell` or any other Nix command you can add
         { allowUnfree = true; }
       to ~/.config/nixpkgs/config.nix.
(use '--show-trace' to show detailed location information)

Ah! Right. It has an unfree license.

Exporting the environment variable and using --impure seems... icky. Alternative "b)" seems to only apply to NixOS, not nixpkgs, and I don't love the idea of changing the global config either... maybe we can fix it in the flake itself?

󱄅  pkgs = import nixpkgs {
    inherit system overlays;
    # 👇 yolo
    config.allowUnfree = true;
  };

$ nix build .#dockerImage
warning: Git tree '/home/amos/catscii' is dirty

Hey, it built!

$ docker load < result
098ab327aa12: Loading layer [==================================================>]  64.83MB/64.83MB
The image catscii:latest already exists, renaming the old one with ID sha256:b78e239c264a2fdf4d6fb63b827abdc2515ae5f4ef3825b7f623bb6ee9cf3b5a to empty string
Loaded image: catscii:latest

Hey, it loaded!

# IMPORTANT NOTE: we're no longer exporting `GEOLITE2_COUNTRY_DB` - it's baked
# into the Docker image

$ docker run --rm --env SENTRY_DSN --env HONEYCOMB_API_KEY --env ANALYTICS_DB --publish 8080:8080 catscii:latest
/nix/store/561wgc73s0x1250hrgp7jm22hhv7yfln-bash-5.2-p15/bin/bash: warning: setlocale: LC_ALL: cannot change locale (en_US.UTF-8)
{"timestamp":"2023-02-21T13:49:06.476209Z","level":"INFO","fields":{"message":"Creating honey client","log.target":"libhoney::client","log.module_path":"libhoney::client","log.file":"/nix/store/eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee-vendor-cargo-deps/2b916d13eeef5c4c978dd7cdbe0195cb3a2cb3e77889acf9f85433ddf74a8e14/libhoney-rust-0.1.6/src/client.rs","log.line":78},"target":"libhoney::client"}
{"timestamp":"2023-02-21T13:49:06.476284Z","level":"INFO","fields":{"message":"transmission starting","log.target":"libhoney::transmission","log.module_path":"libhoney::transmission","log.file":"/nix/store/eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee-vendor-cargo-deps/2b916d13eeef5c4c978dd7cdbe0195cb3a2cb3e77889acf9f85433ddf74a8e14/libhoney-rust-0.1.6/src/transmission.rs","log.line":124},"target":"libhoney::transmission"}
{"timestamp":"2023-02-21T13:49:06.481455Z","level":"INFO","fields":{"message":"Listening on 0.0.0.0:8080"},"target":"catscii"}

Hey, it ran!

$ curl http://localhost:8080/; echo
Something went wrong

Hey, something went wrong!

Debugging what went wrong

The app is running in sort of a weird environment here: it's a release build, so sentry thinks it's "production", but it also has Sentry & Honeycomb keys for "development".

The codepath we're hitting is in root_get_inner, here:

// in `catscii/src/main.rs`

async fn root_get_inner(state: ServerState) -> Response<BoxBody> {
    let tracer = global::tracer("");

    match get_cat_ascii_art(&state.client)
        .with_context(Context::current_with_span(
            tracer.start("get_cat_ascii_art"),
        ))
        .await
    {
        Ok(art) => (
            StatusCode::OK,
            [(header::CONTENT_TYPE, "text/html; charset=utf-8")],
            art,
        )
            .into_response(),
        Err(e) => {
            get_active_span(|span| {
                span.set_status(Status::Error {
                    description: format!("{e}").into(),
                })
            });
            (StatusCode::INTERNAL_SERVER_ERROR, "Something went wrong").into_response()
        }
    }
}

We're not printing anything useful to stdout or stderr, but we are attaching the error to the active opentelemetry span.

So if we open Honeycomb, we should be able to see it.

And yet, I see nothing.

Running the service again with a little more logging enabled reveals the source of the problem:

$ docker run --rm --env RUST_LOG=libhoney::transmission=trace --env SENTRY_DSN --env HONEYCOMB_API_KEY --publish 8080:8080 catscii:latest
/nix/store/561wgc73s0x1250hrgp7jm22hhv7yfln-bash-5.2-p15/bin/bash: warning: setlocale: LC_ALL: cannot change locale (en_US.UTF-8)
{"timestamp":"2023-02-21T13:56:45.083939Z","level":"INFO","fields":{"message":"transmission starting","log.target":"libhoney::transmission","log.module_path":"libhoney::transmission","log.file":"/nix/store/eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee-vendor-cargo-deps/2b916d13eeef5c4c978dd7cdbe0195cb3a2cb3e77889acf9f85433ddf74a8e14/libhoney-rust-0.1.6/src/transmission.rs","log.line":124},"target":"libhoney::transmission"}
{"timestamp":"2023-02-21T13:56:50.244910Z","level":"TRACE","fields":{"message":"Processing data event for dataset `catscii`","log.target":"libhoney::transmission","log.module_path":"libhoney::transmission","log.file":"/nix/store/eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee-vendor-cargo-deps/2b916d13eeef5c4c978dd7cdbe0195cb3a2cb3e77889acf9f85433ddf74a8e14/libhoney-rust-0.1.6/src/transmission.rs","log.line":286},"target":"libhoney::transmission"}
{"timestamp":"2023-02-21T13:56:50.244965Z","level":"TRACE","fields":{"message":"Processing data event for dataset `catscii`","log.target":"libhoney::transmission","log.module_path":"libhoney::transmission","log.file":"/nix/store/eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee-vendor-cargo-deps/2b916d13eeef5c4c978dd7cdbe0195cb3a2cb3e77889acf9f85433ddf74a8e14/libhoney-rust-0.1.6/src/transmission.rs","log.line":286},"target":"libhoney::transmission"}
{"timestamp":"2023-02-21T13:56:50.244983Z","level":"TRACE","fields":{"message":"Processing data event for dataset `catscii`","log.target":"libhoney::transmission","log.module_path":"libhoney::transmission","log.file":"/nix/store/eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee-vendor-cargo-deps/2b916d13eeef5c4c978dd7cdbe0195cb3a2cb3e77889acf9f85433ddf74a8e14/libhoney-rust-0.1.6/src/transmission.rs","log.line":286},"target":"libhoney::transmission"}
{"timestamp":"2023-02-21T13:56:50.345329Z","level":"TRACE","fields":{"message":"Timer expired with 3 event(s)","log.target":"libhoney::transmission","log.module_path":"libhoney::transmission","log.file":"/nix/store/eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee-vendor-cargo-deps/2b916d13eeef5c4c978dd7cdbe0195cb3a2cb3e77889acf9f85433ddf74a8e14/libhoney-rust-0.1.6/src/transmission.rs","log.line":326},"target":"libhoney::transmission"}
{"timestamp":"2023-02-21T13:56:50.345552Z","level":"TRACE","fields":{"message":"Sending payload: [\n    EventData {\n        data: {\n            \"service.name\": String(\"unknown_service\"),\n            \"trace.span_id\": String(\"8dae7119ba0e603b\"),\n            \"duration_ms\": Number(273),\n            \"start_time\": String(\"2023-02-21T13:56:49.971Z\"),\n            \"trace.trace_id\": String(\"4f0d211abaf6d3def49db1e8c68c19a1\"),\n            \"trace.parent_id\": String(\"5181dfe0551a078b\"),\n            \"name\": String(\"api_headers\"),\n            \"span.kind\": String(\"internal\"),\n            \"response.status_code\": Number(0),\n        },\n        time: 2023-02-21T13:56:49.971Z,\n        samplerate: 1,\n    },\n    EventData {\n        data: {\n            \"service.name\": String(\"unknown_service\"),\n            \"trace.span_id\": String(\"5181dfe0551a078b\"),\n            \"duration_ms\": Number(273),\n            \"start_time\": String(\"2023-02-21T13:56:49.971Z\"),\n            \"trace.trace_id\": String(\"4f0d211abaf6d3def49db1e8c68c19a1\"),\n            \"trace.parent_id\": String(\"c5402bd23db803af\"),\n            \"name\": String(\"get_cat_ascii_art\"),\n            \"span.kind\": String(\"internal\"),\n            \"response.status_code\": Number(0),\n        },\n        time: 2023-02-21T13:56:49.971Z,\n        samplerate: 1,\n    },\n    EventData {\n        data: {\n            \"service.name\": String(\"unknown_service\"),\n            \"error\": Bool(true),\n            \"trace.span_id\": String(\"c5402bd23db803af\"),\n            \"duration_ms\": Number(273),\n            \"start_time\": String(\"2023-02-21T13:56:49.971Z\"),\n            \"trace.trace_id\": String(\"4f0d211abaf6d3def49db1e8c68c19a1\"),\n            \"status.message\": String(\"error sending request for url (https://cataas.com/cat): error trying to connect: error:16000069:STORE routines:ossl_store_get0_loader_int:unregistered scheme:crypto/store/store_register.c:237:scheme=file, error:80000002:system library:file_open:reason(2):providers/implementations/storemgmt/file_store.c:267:calling stat(/nix/store/dsf1m9azqqz6c3nqj9yk0nnardqmaia0-openssl-3.0.8/etc/ssl/certs), error:16000069:STORE routines:ossl_store_get0_loader_int:unregistered scheme:crypto/store/store_register.c:237:scheme=file, error:80000002:system library:file_open:reason(2):providers/implementations/storemgmt/file_store.c:267:calling stat(/nix/store/dsf1m9azqqz6c3nqj9yk0nnardqmaia0-openssl-3.0.8/etc/ssl/certs), error:16000069:STORE routines:ossl_store_get0_loader_int:unregistered scheme:crypto/store/store_register.c:237:scheme=file, error:80000002:system library:file_open:reason(2):providers/implementations/storemgmt/file_store.c:267:calling stat(/nix/store/dsf1m9azqqz6c3nqj9yk0nnardqmaia0-openssl-3.0.8/etc/ssl/certs), error:16000069:STORE routines:ossl_store_get0_loader_int:unregistered scheme:crypto/store/store_register.c:237:scheme=file, error:80000002:system library:file_open:reason(2):providers/implementations/storemgmt/file_store.c:267:calling stat(/nix/store/dsf1m9azqqz6c3nqj9yk0nnardqmaia0-openssl-3.0.8/etc/ssl/certs), error:16000069:STORE routines:ossl_store_get0_loader_int:unregistered scheme:crypto/store/store_register.c:237:scheme=file, error:80000002:system library:file_open:reason(2):providers/implementations/storemgmt/file_store.c:267:calling stat(/nix/store/dsf1m9azqqz6c3nqj9yk0nnardqmaia0-openssl-3.0.8/etc/ssl/certs), error:0A000086:SSL routines:tls_post_process_server_certificate:certificate verify failed:ssl/statem/statem_clnt.c:1889: (unable to get local issuer certificate)\"),\n            \"user_agent\": String(\"curl/7.85.0\"),\n            \"name\": String(\"root_get\"),\n            \"span.kind\": String(\"internal\"),\n            \"response.status_code\": Number(2),\n        },\n        time: 2023-02-21T13:56:49.971Z,\n        samplerate: 1,\n    },\n]","log.target":"libhoney::transmission","log.module_path":"libhoney::transmission","log.file":"/nix/store/eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee-vendor-cargo-deps/2b916d13eeef5c4c978dd7cdbe0195cb3a2cb3e77889acf9f85433ddf74a8e14/libhoney-rust-0.1.6/src/transmission.rs","log.line":426},"target":"libhoney::transmission"}

(This happened while running curl http://localhost:8080 from another shell).

In case your brain doesn't have a built-in JSON.parse function yet, here's a human-friendlier version of this:

error sending request for url (https://cataas.com/cat)
error trying to connect
error:16000069:STORE routines:ossl_store_get0_loader_int:unregistered scheme:crypto/store/store_register.c:237:scheme=file, error:80000002:system library:file_open:reason(2):providers/implementations/storemgmt/file_store.c:267:calling stat(/nix/store/dsf1m9azqqz6c3nqj9yk0nnardqmaia0-openssl-3.0.8/etc/ssl/certs)
error:16000069:STORE routines:ossl_store_get0_loader_int:unregistered scheme:crypto/store/store_register.c:237:scheme=file, error:80000002:system library:file_open:reason(2):providers/implementations/storemgmt/file_store.c:267:calling stat(/nix/store/dsf1m9azqqz6c3nqj9yk0nnardqmaia0-openssl-3.0.8/etc/ssl/certs)
error:16000069:STORE routines:ossl_store_get0_loader_int:unregistered scheme:crypto/store/store_register.c:237:scheme=file, error:80000002:system library:file_open:reason(2):providers/implementations/storemgmt/file_store.c:267:calling stat(/nix/store/dsf1m9azqqz6c3nqj9yk0nnardqmaia0-openssl-3.0.8/etc/ssl/certs)
error:16000069:STORE routines:ossl_store_get0_loader_int:unregistered scheme:crypto/store/store_register.c:237:scheme=file, error:80000002:system library:file_open:reason(2):providers/implementations/storemgmt/file_store.c:267:calling stat(/nix/store/dsf1m9azqqz6c3nqj9yk0nnardqmaia0-openssl-3.0.8/etc/ssl/certs)
error:16000069:STORE routines:ossl_store_get0_loader_int:unregistered scheme:crypto/store/store_register.c:237:scheme=file, error:80000002:system library:file_open:reason(2):providers/implementations/storemgmt/file_store.c:267:calling stat(/nix/store/dsf1m9azqqz6c3nqj9yk0nnardqmaia0-openssl-3.0.8/etc/ssl/certs)
error:0A000086:SSL routines:tls_post_process_server_certificate:certificate verify failed:ssl/statem/statem_clnt.c:1889
(unable to get local issuer certificate)

Oh! It can't find the CA certificates to verify cataas.com's certificate!

Why yes, exactly!

When establishing a TLS connection, a lot of things happen (as wonderfully explained in The Illustrated TLS 1.3 Connection), but an important one is: the server presents a chain of certificates, starting with a certificate for the domain in question (here, cataas.com), and ending with something you trust.

At the time of this writing, the certificate chain for cataas.com goes:

ISRG Root X1
- R3
  - cataas.com

And how do we know we trust "ISRG Root X1", a CA ("Certificate Authority") from Let's Encrypt?

Well, we have a file on disk that says so!

❯ openssl x509 -in /etc/ssl/certs/ISRG_Root_X1.pem -nocert -text
Certificate:
    Data:
        Version: 3 (0x2)
        Serial Number:
            82:10:cf:b0:d2:40:e3:59:44:63:e0:bb:63:82:8b:00
        Signature Algorithm: sha256WithRSAEncryption
        Issuer: C = US, O = Internet Security Research Group, CN = ISRG Root X1
        Validity
            Not Before: Jun  4 11:04:38 2015 GMT
            Not After : Jun  4 11:04:38 2035 GMT
        Subject: C = US, O = Internet Security Research Group, CN = ISRG Root X1
        Subject Public Key Info:
            Public Key Algorithm: rsaEncryption
                Public-Key: (4096 bit)
                Modulus:
                    00:ad:e8:24:73:f4:14:37:f3:9b:9e:2b:57:28:1c:
                    87:be:dc:b7:df:38:90:8c:6e:3c:e6:57:a0:78:f7:
                    75:c2:a2:fe:f5:6a:6e:f6:00:4f:28:db:de:68:86:
                    6c:44:93:b6:b1:63:fd:14:12:6b:bf:1f:d2:ea:31:
                    9b:21:7e:d1:33:3c:ba:48:f5:dd:79:df:b3:b8:ff:
                    12:f1:21:9a:4b:c1:8a:86:71:69:4a:66:66:6c:8f:
                    7e:3c:70:bf:ad:29:22:06:f3:e4:c0:e6:80:ae:e2:
                    4b:8f:b7:99:7e:94:03:9f:d3:47:97:7c:99:48:23:
                    53:e8:38:ae:4f:0a:6f:83:2e:d1:49:57:8c:80:74:
                    b6:da:2f:d0:38:8d:7b:03:70:21:1b:75:f2:30:3c:
                    fa:8f:ae:dd:da:63:ab:eb:16:4f:c2:8e:11:4b:7e:
                    cf:0b:e8:ff:b5:77:2e:f4:b2:7b:4a:e0:4c:12:25:
                    0c:70:8d:03:29:a0:e1:53:24:ec:13:d9:ee:19:bf:
                    10:b3:4a:8c:3f:89:a3:61:51:de:ac:87:07:94:f4:
                    63:71:ec:2e:e2:6f:5b:98:81:e1:89:5c:34:79:6c:
                    76:ef:3b:90:62:79:e6:db:a4:9a:2f:26:c5:d0:10:
                    e1:0e:de:d9:10:8e:16:fb:b7:f7:a8:f7:c7:e5:02:
                    07:98:8f:36:08:95:e7:e2:37:96:0d:36:75:9e:fb:
                    0e:72:b1:1d:9b:bc:03:f9:49:05:d8:81:dd:05:b4:
                    2a:d6:41:e9:ac:01:76:95:0a:0f:d8:df:d5:bd:12:
                    1f:35:2f:28:17:6c:d2:98:c1:a8:09:64:77:6e:47:
                    37:ba:ce:ac:59:5e:68:9d:7f:72:d6:89:c5:06:41:
                    29:3e:59:3e:dd:26:f5:24:c9:11:a7:5a:a3:4c:40:
                    1f:46:a1:99:b5:a7:3a:51:6e:86:3b:9e:7d:72:a7:
                    12:05:78:59:ed:3e:51:78:15:0b:03:8f:8d:d0:2f:
                    05:b2:3e:7b:4a:1c:4b:73:05:12:fc:c6:ea:e0:50:
                    13:7c:43:93:74:b3:ca:74:e7:8e:1f:01:08:d0:30:
                    d4:5b:71:36:b4:07:ba:c1:30:30:5c:48:b7:82:3b:
                    98:a6:7d:60:8a:a2:a3:29:82:cc:ba:bd:83:04:1b:
                    a2:83:03:41:a1:d6:05:f1:1b:c2:b6:f0:a8:7c:86:
                    3b:46:a8:48:2a:88:dc:76:9a:76:bf:1f:6a:a5:3d:
                    19:8f:eb:38:f3:64:de:c8:2b:0d:0a:28:ff:f7:db:
                    e2:15:42:d4:22:d0:27:5d:e1:79:fe:18:e7:70:88:
                    ad:4e:e6:d9:8b:3a:c6:dd:27:51:6e:ff:bc:64:f5:
                    33:43:4f
                Exponent: 65537 (0x10001)
        X509v3 extensions:
            X509v3 Key Usage: critical
                Certificate Sign, CRL Sign
            X509v3 Basic Constraints: critical
                CA:TRUE
            X509v3 Subject Key Identifier:
                79:B4:59:E6:7B:B6:E5:E4:01:73:80:08:88:C8:1A:58:F6:E9:9B:6E
    Signature Algorithm: sha256WithRSAEncryption
    Signature Value:
        55:1f:58:a9:bc:b2:a8:50:d0:0c:b1:d8:1a:69:20:27:29:08:
        ac:61:75:5c:8a:6e:f8:82:e5:69:2f:d5:f6:56:4b:b9:b8:73:
        10:59:d3:21:97:7e:e7:4c:71:fb:b2:d2:60:ad:39:a8:0b:ea:
        17:21:56:85:f1:50:0e:59:eb:ce:e0:59:e9:ba:c9:15:ef:86:
        9d:8f:84:80:f6:e4:e9:91:90:dc:17:9b:62:1b:45:f0:66:95:
        d2:7c:6f:c2:ea:3b:ef:1f:cf:cb:d6:ae:27:f1:a9:b0:c8:ae:
        fd:7d:7e:9a:fa:22:04:eb:ff:d9:7f:ea:91:2b:22:b1:17:0e:
        8f:f2:8a:34:5b:58:d8:fc:01:c9:54:b9:b8:26:cc:8a:88:33:
        89:4c:2d:84:3c:82:df:ee:96:57:05:ba:2c:bb:f7:c4:b7:c7:
        4e:3b:82:be:31:c8:22:73:73:92:d1:c2:80:a4:39:39:10:33:
        23:82:4c:3c:9f:86:b2:55:98:1d:be:29:86:8c:22:9b:9e:e2:
        6b:3b:57:3a:82:70:4d:dc:09:c7:89:cb:0a:07:4d:6c:e8:5d:
        8e:c9:ef:ce:ab:c7:bb:b5:2b:4e:45:d6:4a:d0:26:cc:e5:72:
        ca:08:6a:a5:95:e3:15:a1:f7:a4:ed:c9:2c:5f:a5:fb:ff:ac:
        28:02:2e:be:d7:7b:bb:e3:71:7b:90:16:d3:07:5e:46:53:7c:
        37:07:42:8c:d3:c4:96:9c:d5:99:b5:2a:e0:95:1a:80:48:ae:
        4c:39:07:ce:cc:47:a4:52:95:2b:ba:b8:fb:ad:d2:33:53:7d:
        e5:1d:4d:6d:d5:a1:b1:c7:42:6f:e6:40:27:35:5c:a3:28:b7:
        07:8d:e7:8d:33:90:e7:23:9f:fb:50:9c:79:6c:46:d5:b4:15:
        b3:96:6e:7e:9b:0c:96:3a:b8:52:2d:3f:d6:5b:e1:fb:08:c2:
        84:fe:24:a8:a3:89:da:ac:6a:e1:18:2a:b1:a8:43:61:5b:d3:
        1f:dc:3b:8d:76:f2:2d:e8:8d:75:df:17:33:6c:3d:53:fb:7b:
        cb:41:5f:ff:dc:a2:d0:61:38:e1:96:b8:ac:5d:8b:37:d7:75:
        d5:33:c0:99:11:ae:9d:41:c1:72:75:84:be:02:41:42:5f:67:
        24:48:94:d1:9b:27:be:07:3f:b9:b8:4f:81:74:51:e1:7a:b7:
        ed:9d:23:e2:be:e0:d5:28:04:13:3c:31:03:9e:dd:7a:6c:8f:
        c6:07:18:c6:7f:de:47:8e:3f:28:9e:04:06:cf:a5:54:34:77:
        bd:ec:89:9b:e9:17:43:df:5b:db:5f:fe:8e:1e:57:a2:cd:40:
        9d:7e:62:22:da:de:18:27

That's why, if you do:

$ curl --head https://cataas.com/
HTTP/1.1 404 Not Found
Server: nginx
Date: Wed, 13 Mar 2024 18:40:20 GMT
Connection: keep-alive
Set-Cookie: session=41cd42f1-552a-479a-91a1-2e0ddb837e3e; Path=/; SameSite=Strict; Secure; HttpOnly
Access-Control-Allow-Origin: *
Access-Control-Allow-Headers: X-Requested-With, Content-Type, Accept, Origin, Authorization
Access-Control-Allow-Methods: GET, POST, PUT, DELETE, OPTIONS

...it works!

But when our program inside the Docker image tries to do so, it does not work. In fact, even outside the Docker image it doesn't work, because it links against a build of openssl that looks for CA certificates not in /etc/ssl/certs (like an Ubuntu package would), but in /nix/store/dsf1m9azqqz6c3nqj9yk0nnardqmaia0-openssl-3.0.8/etc/ssl/certs (like a nix package would).

So, long story short, we need to pull that into the Docker image:

󱄅dockerImage = pkgs.dockerTools.buildImage {
  name = "catscii";
  tag = "latest";
  # new!                👇
  copyToRoot = [ bin pkgs.cacert ];
  config = {
    Cmd = [ "${bin}/bin/catscii" ];
    Env = with pkgs; [ "GEOLITE2_COUNTRY_DB=${clash-geoip}/etc/clash/Country.mmdb" ];
  };
};

Wait wait, but why didn't we see it in Honeycomb?

Well, how do you think events are sent to Honeycomb?

Over HTTPS? Oh.... Ohhhhhhhhhhh!

Yeah.

Streaming docker images

Let's build this once again:

$ nix build .#dockerImage && docker load < result
warning: Git tree '/home/amos/catscii' is dirty
a0d69db324f4: Loading layer [==================================================>]  65.81MB/65.81MB
The image catscii:latest already exists, renaming the old one with ID sha256:6bd980414ca2a765952467b7b7667c892567c824a36ddb1065d911a2f822cce9 to empty string
Loaded image: catscii:latest

Say, this seems a little wasteful, no? Writing the whole image to disk, only to import it back into the docker registry right after?

You're right! We can live with that, of course, but say we didn't, say we wanted to really obsess over that, we could switch to streamLayeredImage.

Let's do that now!

󱄅#                  was `buildImage` 👇
dockerImage = pkgs.dockerTools.streamLayeredImage {
  name = "catscii";
  tag = "latest";
  # 👇 was `copyToRoot`
  contents = [ bin pkgs.cacert ];
  config = {
    Cmd = [ "${bin}/bin/catscii" ];
    Env = with pkgs; [ "GEOLITE2_COUNTRY_DB=${clash-geoip}/etc/clash/Country.mmdb" ];
  };
};

Loading the image into the docker registry is now a bit different!

result is no longer a gzipped tarball (.tar.gz), but it is a script that streams out an uncompressed tarball (.tar).

So, we can call it and pipe the output to docker load.

$ nix build .#dockerImage && ./result | docker load
warning: Git tree '/home/amos/catscii' is dirty
No 'fromImage' provided
Creating layer 1 from paths: ['/nix/store/jdjpni8kq3i95dj1d49nlf9m10wl0kqq-libunistring-1.0']
Creating layer 2 from paths: ['/nix/store/na1irnycfp8z5mab0g5jvrnhnscsaqsb-libidn2-2.3.2']
Creating layer 3 from paths: ['/nix/store/lqz6hmd86viw83f9qll2ip87jhb7p1ah-glibc-2.35-224']
Creating layer 4 from paths: ['/nix/store/9dz5lmff9ywas225g6cpn34s0wbldnxa-zlib-1.2.13']
Creating layer 5 from paths: ['/nix/store/dsf1m9azqqz6c3nqj9yk0nnardqmaia0-openssl-3.0.8']
Creating layer 6 from paths: ['/nix/store/zqf9r5d9yv4ccv64ja8xjn8kasgqg3cy-sqlite-3.40.1']
Creating layer 7 from paths: ['/nix/store/dvfh98mvqish3jsih29rs3r45qn3yfpf-catscii-0.1.0']
Creating layer 8 from paths: ['/nix/store/l1amkbsx8mqv11b4mg98f9lyw5nkrcbv-clash-geoip-20230112']
Creating layer 9 from paths: ['/nix/store/0mm127hlf3rsdph4p34385qxsrph20rp-nss-cacert-3.86']
Creating layer 10 with customisation...
Adding manifests...
Done.
0b99676422a9: Loading layer [==================================================>]  1.812MB/1.812MB
dc71b1c4d9c2: Loading layer [==================================================>]    297kB/297kB
541c11727f9e: Loading layer [==================================================>]  30.77MB/30.77MB
d86a062e6369: Loading layer [==================================================>]  143.4kB/143.4kB
e21cc889e6d8: Loading layer [==================================================>]  6.482MB/6.482MB
26544d61db4d: Loading layer [==================================================>]  1.485MB/1.485MB
1af5c770e073: Loading layer [==================================================>]  9.114MB/9.114MB
9c32b3e8b0f5: Loading layer [==================================================>]  5.663MB/5.663MB
77d56c064e6a: Loading layer [==================================================>]  501.8kB/501.8kB
314943a5b800: Loading layer [==================================================>]  10.24kB/10.24kB
The image catscii:latest already exists, renaming the old one with ID sha256:37a94963597827d5b7ceda467d44a501c38121bb7f5df736aec2f7cb0e9c18ca to empty string
Loaded image: catscii:latest

You'll notice this image has layers (we can control how many layers it has with maxLayers), so pushing updates should be faster, since dependencies like openssl, glibc, zlib etc. seldom change!

Note that our image is still delightfully small: dive catscii:latest shows a total image size of 55MB. Adding ca-certs only cost us 486 kB:

dive showing the layer where we added ca-certs

Let's run it just like we did before:

$ docker run --rm -e SENTRY_DSN -e HONEYCOMB_API_KEY -e ANALYTICS_DB -p 8080:8080 catscii:latest
/nix/store/561wgc73s0x1250hrgp7jm22hhv7yfln-bash-5.2-p15/bin/bash: warning: setlocale: LC_ALL: cannot change locale (en_US.UTF-8)
{"timestamp":"2023-02-21T14:33:52.577377Z","level":"INFO","fields":{"message":"Creating honey client","log.target":"libhoney::client","log.module_path":"libhoney::client","log.file":"/nix/store/eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee-vendor-cargo-deps/2b916d13eeef5c4c978dd7cdbe0195cb3a2cb3e77889acf9f85433ddf74a8e14/libhoney-rust-0.1.6/src/client.rs","log.line":78},"target":"libhoney::client"}
{"timestamp":"2023-02-21T14:33:52.577573Z","level":"INFO","fields":{"message":"transmission starting","log.target":"libhoney::transmission","log.module_path":"libhoney::transmission","log.file":"/nix/store/eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee-vendor-cargo-deps/2b916d13eeef5c4c978dd7cdbe0195cb3a2cb3e77889acf9f85433ddf74a8e14/libhoney-rust-0.1.6/src/transmission.rs","log.line":124},"target":"libhoney::transmission"}
{"timestamp":"2023-02-21T14:33:52.645842Z","level":"INFO","fields":{"message":"Listening on 0.0.0.0:8080"},"target":"catscii"}

And finally, we have our sweet ascii art cats again!

Deploying to fly.io

Deploying works much the same as it did before - we still have to opt out of fly.io's "remote builders", since we really do want to push a local image there.

Our Justfile could look like this:

# just manual: https://github.com/casey/just#readme

_default:
  just --list

docker:
  #!/bin/bash -eux
  nix build .#dockerImage
  ./result | docker load

deploy:
  just docker
  fly deploy --local-only

But of course, we'll want to to add just and flyctl to our dev shell first:

󱄅  devShells.default = mkShell
    {
      inputsFrom = [ bin ];
      # note: I ended up keeping `docker` in my dev shell 🤷
      buildInputs = with pkgs; [ dive docker shadow flyctl just ];
    };

Then,fly auth login:

$ fly auth login
(cut)

And... let's just check our fly.toml one last time.. oh, right! We have that in there:

[env]
GEOLITE2_COUNTRY_DB = "/db/GeoLite2-Country.mmdb" # 🗑️ remove me!
ANALYTICS_DB = "/db/analytics.db"

We should remove that GEOLITE2_COUNTRY_DB line from there - that environment variable is baked into the Docker image now.

And then we're good to go!

$ just deploy
just docker
+ nix build .#dockerImage
warning: Git tree '/home/amos/catscii' is dirty
+ ./result
+ docker load
No 'fromImage' provided
Creating layer 1 from paths: ['/nix/store/jdjpni8kq3i95dj1d49nlf9m10wl0kqq-libunistring-1.0']
Creating layer 2 from paths: ['/nix/store/na1irnycfp8z5mab0g5jvrnhnscsaqsb-libidn2-2.3.2']
Creating layer 3 from paths: ['/nix/store/lqz6hmd86viw83f9qll2ip87jhb7p1ah-glibc-2.35-224']
Creating layer 4 from paths: ['/nix/store/9dz5lmff9ywas225g6cpn34s0wbldnxa-zlib-1.2.13']
Creating layer 5 from paths: ['/nix/store/dsf1m9azqqz6c3nqj9yk0nnardqmaia0-openssl-3.0.8']
Creating layer 6 from paths: ['/nix/store/zqf9r5d9yv4ccv64ja8xjn8kasgqg3cy-sqlite-3.40.1']
Creating layer 7 from paths: ['/nix/store/dvfh98mvqish3jsih29rs3r45qn3yfpf-catscii-0.1.0']
Creating layer 8 from paths: ['/nix/store/l1amkbsx8mqv11b4mg98f9lyw5nkrcbv-clash-geoip-20230112']
Creating layer 9 from paths: ['/nix/store/0mm127hlf3rsdph4p34385qxsrph20rp-nss-cacert-3.86']
Creating layer 10 with customisation...
Adding manifests...
Done.
Loaded image: catscii:latest
fly deploy --local-only
Update available 0.0.456 -> v0.0.462.
Run "flyctl version update" to upgrade.
==> Verifying app config
--> Verified app config
==> Building image
Searching for image 'catscii' locally...
image found: sha256:faf87069d1dbea4b141353485cfbd3f5f7b5ef3f0c1e3f8e37eb4ac119f78890
==> Pushing image to fly
The push refers to repository [registry.fly.io/old-frost-6294]
314943a5b800: Pushed
77d56c064e6a: Pushed
9c32b3e8b0f5: Pushed
1af5c770e073: Pushed
26544d61db4d: Pushed
e21cc889e6d8: Pushed
d86a062e6369: Pushed
541c11727f9e: Pushed
dc71b1c4d9c2: Pushed
0b99676422a9: Pushed
deployment-01GST6J50SRWXCE0MK0W78G2D3: digest: sha256:107885f7edc0b67b5dea9843b324fc3d6977a3697f9f6d74a183075aa792f325 size: 2417
--> Pushing image done
==> Creating release
--> release v10 created

--> You can detach the terminal anytime without stopping the deployment
==> Monitoring deployment
Logs: https://fly.io/apps/old-frost-6294/monitoring

v10 is being deployed
 1 desired, 1 placed, 0 healthy, 0 unhealthy [restarts: 1]

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Comment on /r/fasterthanlime

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Here's another article just for you:

Remote development with Rust on fly.io

Jun 20, 2022

1 hour 43 min #rust · #tokio · #io-uring · #bpf · #fly.io

Disclaimer:

At the time of this writing, I benefit from the fly.io "Employee Free Tier". I don't pay for side projects hosted there "within reasonable limits". The project discussed here qualifies for that.

Why you might want a remote dev environment

Fearmongering aside — and Cthulhu knows there's been a bunch, since — there's a bunch of reasons to want a remote dev environment.