From 3615d89bb08e2f01fccb00a0283bc6ea43fd449d Mon Sep 17 00:00:00 2001
From: Mark Hansen <markhansen@google.com>
Date: Sat, 20 Feb 2021 15:01:25 +1100
Subject: [PATCH] Reuse docker images where possible

Should speed up CI docker image building.

Inspiration from
https://blog.callr.tech/building-docker-images-with-gitlab-ci-best-practices/
---
 .gitlab-ci.yml | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 9eda7bd00..387f54bbd 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -585,8 +585,10 @@ deployment:
     - tags
   script:
     - cd ci/$IMAGE
-    # Build and push with git commit SHA tag
-    - docker build -t $CI_REGISTRY/graphviz/graphviz/$IMAGE:$CI_COMMIT_SHA .
+    # fetches the :latest image (not failing if image is not found) for caching
+    - docker pull $CI_REGISTRY/graphviz/graphviz/$IMAGE:latest || true
+    # Build and push with git commit SHA tag, reusing layers from the :latest image if possible
+    - docker build -t $CI_REGISTRY/graphviz/graphviz/$IMAGE:$CI_COMMIT_SHA --cache-from $CI_REGISTRY/graphviz/graphviz/$IMAGE:latest .
     - docker push     $CI_REGISTRY/graphviz/graphviz/$IMAGE:$CI_COMMIT_SHA
     # Re-tag, push to :latest tag
     - docker tag $CI_REGISTRY/graphviz/graphviz/$IMAGE:$CI_COMMIT_SHA $CI_REGISTRY/graphviz/graphviz:latest
-- 
2.40.0