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Cache Docker Image #147

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merged 1 commit into from
Feb 12, 2021
Merged

Cache Docker Image #147

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21 changes: 20 additions & 1 deletion .github/workflows/continuous-integration.yml
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Original file line number Diff line number Diff line change
Expand Up @@ -19,12 +19,26 @@ jobs:
uses: actions/checkout@v2
- name: Set up Docker
run: docker network create test
- id: cache-docker
uses: actions/cache@v2
with:
path: /tmp/docker-save
key:
docker-save-${{ hashFiles('Dockerfile', 'Gemfile.lock',
'package-lock.json') }}
- name: Load cached Docker image
run: docker load -i /tmp/docker-save/snapshot.tar || true
if: steps.cache-docker.outputs.cache-hit == 'true'
- name: Set up Postgres
run:
docker run -d --name pg --network test -e POSTGRES_USER=test -e
POSTGRES_HOST_AUTH_METHOD=trust -p 5432:5432 postgres:11
- name: Build a new Docker image
run: docker build . --build-arg RAILS_ENV=test -t app:test
run: |
docker build . \
--build-arg RAILS_ENV=test \
-t app:test \
--cache-from app:test
- name: Run the tests
run: |
docker run --name test-container \
Expand All @@ -33,3 +47,8 @@ jobs:
-e DATABASE_CLEANER_ALLOW_REMOTE_DATABASE_URL=true \
-e DATABASE_URL=postgres://test@pg:5432/app_test \
app:test bundle exec rake
- name: Prepare Docker cache
run:
mkdir -p /tmp/docker-save && docker save app:test -o
/tmp/docker-save/snapshot.tar && ls -lh /tmp/docker-save
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if: always() && steps.cache-docker.outputs.cache-hit != 'true'
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Do we want to update the cache even if there's a test failure? Feels like it would be better to keep the cache to those images that pass.

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I think there may be value in sticking with the initial approach.

I'm imaginging the scenario where a pull request adds a new dependency to one of the earlier docker layers. The CI job fails due to application tests which are sourced by one of the last Docker layers. Given this PR is likely to generate another CI run which only changes the application layer, there is value in having a cached dependency layer on hand.

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Yep, that's exactly the scenario I envisaged

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I guess I was worried about broken stuff sitting in the cache and causing bugs (but I guess we should trust Docker). Is the cache isolated to a branch? Will a cache from a branch replace the main cache (and therefore mean everyone not on that branch will have slower builds)? Don't feel super strongly either way, though.