Add txt files for docker builds

[SteffenDE]

As mentioned in #185, looking for Bob's docker images on Docker Hub is often a painful experience. Furthermore, phx.gen.release --docker frequently fails because the Docker Hub API times out when querying for the correct image to use.

To address this, I'm proposing to add a new txt file similar to https://builds.hex.pm/builds/elixir/builds.txt, which lists the available Docker images based on the following schema:

• https://builds.hex.pm/builds/docker/hexpm-elixir-ELIXIR_VSN-erlang-OTP_VSN.txt - lists all image tags for the given Elixir and OTP version

This is what phx.gen.release --docker would query when trying to find the right image for the currently running Elixir and OTP versions. (If you didn't know, the task does not try to get the latest version, but instead create a Docker image for the locally running versions instead).

It would look like this

# https://builds.hex.pm/builds/docker/hexpm-elixir-1.19.5-erlang-28.3.1.txt
1.19.5-erlang-28.3.1-ubuntu-noble-20260210.1 linux/amd64,linux/arm64/v8
1.19.5-erlang-28.3.1-debian-trixie-20260202-slim linux/amd64,linux/arm64/v8
1.19.5-erlang-28.3.1-debian-bookworm-20260202-slim linux/amd64,linux/arm64/v8
1.19.5-erlang-28.3.1-debian-bookworm-20260202 linux/amd64,linux/arm64/v8
1.19.5-erlang-28.3.1-debian-trixie-20260202 linux/amd64,linux/arm64/v8
...

See https://hex-bob-docker.steffend.me/hexpm-elixir-1.19.5-erlang-28.3.1.txt.

The exact format can of course be different, but I think it should contain the image tag and available architectures for that tag.

Whenever Bob builds a new image, it appends to the file for the given versions. Those files are basically append-only.

• https://builds.hex.pm/builds/docker/hexpm-elixir-latest-major-minor.txt - lists all of the latest images

The idea behind that file is to make it easy to find the latest builds for a given Elixir and Erlang major-minor version:

1.19.5-erlang-28.3.1
1.19.5-erlang-28.2
1.19.5-erlang-28.1.1
1.19.5-erlang-28.0.2
1.18.4-erlang-28.3.1
...

A client can then look up the specific version file to find all builds. If someone wants to find the latest version, they just need to look at the first line of the file.

This file would be rewritten whenever frequently, such that only the latest major+minor versions are listed. See https://hex-bob-docker.steffend.me/hexpm-elixir-latest-major-minor.txt.

Based on those files, in the future there could also be a LiveView based UI to look up the available versions in a more user-friendly way.

cc @wojtekmach

(I used a LiveBook to fetch all the available Docker Hub data for most versions. If anyone's interested in it, it's here. If this was incorporated into Bob, I'm sure that there's a better way to know what to write instead of fetching all possible options from the Hub)

[wojtekmach]

I'm very keen on finally addressing this problem, thank you for bringing this up.

https://builds.hex.pm/builds/docker/hexpm-elixir-ELIXIR_VSN-erlang-OTP_VSN.txt

nitpick: I'd consider changing hexpm-elixir- to elixir: or elixir/, e.g.:

• https://builds.hex.pm/builds/docker/elixir:1.19.5-erlang-28.3.1.txt

Which is similar to:

$ docker pull hexpm/elixir:1.19.5-erlang-28.3.1-ubuntu-noble-20260210.1

No big deal either way. hexpm-elixir- has the advantage that it'd all be a flat list of files.

https://builds.hex.pm/builds/docker/hexpm-elixir-latest-major-minor.txt

Yup sounds good to me. I like that we include latest Elixir major/minor and OTP major/minor. We could make that part of the file name, call it literally:

https://builds.hex.pm/builds/docker/elixir:x.y-erlang-x.y.txt

akin to https://builds.hex.pm/installs/hex-1.x.csv. Dunno if it makes it more or less explicit. 😅

[SteffenDE]

Yeah I don't mind the exact file naming, so builds/docker/elixir:tag.txt is good, same for the x.y 👍

Bob seems pretty much stateless right now (no database), just storing data in S3 and Docker Hub. Does it build images in parallel? If so, the only place where we need to be careful is to not overwrite the elixir:VSN-erlang-OTPVSN.txt files. But S3 has conditional puts, so we can handle that too. The x.y file could be regenerated whenever the Elixir/OTP builds.txt changes.

Then we'd also need code to initially generate the files for the already existing builds. Instead of doing what I did in my livebook, it might be easier to just query all existing tags in DockerHub.

[fhunleth]

Just in case others run into this issue, I (or really Claude) made https://fhunleth.github.io/latest_elixir/. I did this before learning of this issue so it's not what's proposed here, but might help in the interim. Also, I hadn't appreciated that Bob had posted 200K+ tags!