Add a docker recipe for rebar3 itself

[lrascao]

Based on the closest Alpine Erlang version currently supported by
rebar3. Allows people to mix and match different versions of
the Erlang VM and rebar3 using multi-stage docker builds.

[ferd]

Probably makes sense for us to have one that way.

I was wondering if it would also make sense to go for something as in https://adoptingerlang.org/docs/production/docker/ and push for a multi-stage build that handles releases as a template but I guess that's fully distinct from what we have here.

[lrascao]

I suppose this PR is a step in that direction, i'm using those very same instructions at adoptingerlang.org and felt the need to pull down a specific rebar3 version.

For future reference purposes something like this:

# syntax = docker/dockerfile:experimental

# Pull down the desired rebar3 image version
FROM rebar3:latest as rebar3

FROM docker.pkg.github.com/adoptingerlang/service_discovery/erlang:22.1.1-alpine as builder

 # copy the rebar3 over from the rebar3 docker image and
 # overwriting the one being used by alpine
COPY --from=rebar3 /opt/.cache/rebar3 /opt/.cache/rebar3
COPY --from=rebar3 /usr/local/bin/rebar3 /usr/local/bin/rebar3

[tsloughter]

I'd prefer this used rebar3 local install. You can set HOME to /opt in the instruction and then create a link from /usr/local/bin/rebar3 to /opt/.cache/rebar3/bin/rebar3.

Patch I've been meaning to make is to have local install properly use XDG_CACHE_DIR and then you could set that to /opt/ and it'd install to /opt/rebar3/ instead of that .cache directory.

[lrascao]

updated

[lrascao]

update the comment above. With these changes, you'll also need to copy over /opt/.cache/rebar3 besides the rebar3 binary, is this better somehow?

[tsloughter]

Oh, didn't think about the use of copying it into another image. Argh, annoying, it is far better to use the unpacked version when calling from Entrypoint, so people default to that, but is a pain when copying.

I guess you can just undo my suggested change. It'd probably be confusing if there was both the rebar3 escript and the local install copy.

[lrascao]

If properly documented, people will copy/paste the two lines over to their own docker images. What is being offered through the local install method additionally to install -v?
btw, install -v is the method used in the official Erlang docker images

[tsloughter]

Yea, I want to change that in those too.

local install offers it not being an escript, which among making it slightly more efficient means the terminal doesn't get all screwed up if the user ctrl-c's out of the shell.

[lrascao]

ah nice, we should keep local install then