Github Action Cache question with containers - caching

Question

I got a quick question and I can't find docs on it (maybe it is impossible)
How can I retrieve what has been built from a container (like this) :
prod-dependencies:
name: Production Dependencies
runs-on: ubuntu-20.04
container: elixir:1.11-alpine
env:
MIX_ENV: prod
steps:
- name: Checkout
uses: actions/checkout#v2
with:
fetch-depth: 0
- name: Retrieve Cached Dependencies
uses: actions/cache#v2
id: mix-prod-cache
with:
path: |
${{ github.workspace }}/deps
${{ github.workspace }}/_build
key: PROD-${{ hashFiles('mix.lock') }}
- name: Install Dependencies
if: steps.mix-prod-cache.outputs.cache-hit != 'true'
run: |
apk add build-base rust cargo
mix do local.hex --force, local.rebar --force, deps.get --only prod, deps.compile
I need to build on Alpine since I am deploying on Alpine and some C libs are different for the Erlang VM to work.
So here it is the place where I build dependencies and I want to put them on cache for the subsequent jobs but the cache is never populated. According to doc GitHub mount a volume with containers to retrieve artifacts but I must miss use it.
Thanks a lot for your help.

Answer 1

Here is a sample Github workflow for an Elixir app with a Postgres database that utilizes the action/cache#v2. Note that it defines 2 separate steps for restoring the deps and _build directories. In this workflow, the mix deps.get and mix compile steps are always run: they should execute very quickly if the cache is restored.
Adapted from this workflow
name: Test
on:
pull_request:
branches:
- develop
paths-ignore:
- 'docs/**'
- '*.md'
jobs:
test:
name: Lint and test
runs-on: ubuntu-18.04
env:
MIX_ENV: test
services:
db:
image: postgres:11
ports: ['5432:5432']
env:
POSTGRES_PASSWORD: postgres
options: >-
--health-cmd pg_isready
--health-interval 10s
--health-timeout 5s
--health-retries 5
steps:
- uses: actions/checkout#v2
- uses: erlef/setup-elixir#v1
with:
otp-version: '23.1.2'
elixir-version: '1.11.2'
- name: Configure SSH for private Repos
uses: webfactory/ssh-agent#v0.4.1
with:
ssh-private-key: ${{ secrets.HEADLESS_PRIV }}
- name: Restore the deps cache
uses: actions/cache#v2
id: deps-cache-restore
with:
path: deps
key: ${{ runner.os }}-deps-mixlockhash-${{ hashFiles(format('{0}{1}', github.workspace, '/mix.lock')) }}
restore-keys: |
${{ runner.os }}-deps-
- name: Restore the _build cache
uses: actions/cache#v2
id: build-cache-restore
with:
path: _build
key: ${{ runner.os }}-build-mixlockhash-${{ hashFiles(format('{0}{1}', github.workspace, '/mix.lock')) }}
restore-keys: |
${{ runner.os }}-build-
- name: Get/update Mix dependencies
run: |
mix local.hex --force
mix local.rebar
mix deps.get
- name: Compile
run: mix compile
- name: Create database
run: mix ecto.create
- name: Migrate database
run: mix ecto.migrate
- name: Test
run: mix test