From 3b016bb0eee7d798c71fd2eb1afd40ec5cb24d90 Mon Sep 17 00:00:00 2001
From: Robert Prehn <3952444+prehnRA@users.noreply.github.com>
Date: Thu, 10 Jun 2021 14:17:35 -0500
Subject: [PATCH] feat: Cache intermediate docker images

---
 .gitlab-ci.yml            | 10 ++--------
 Dockerfile                |  4 ++--
 script/ci-docker-build    | 27 +++++++++++++++++++++++++++
 script/ci-docker-prebuild | 17 +++++++++++++++++
 4 files changed, 48 insertions(+), 10 deletions(-)
 create mode 100755 script/ci-docker-build
 create mode 100755 script/ci-docker-prebuild

diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 1c6a4e95..bbc87698 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -36,15 +36,9 @@ build_image_for_commit:
   services:
     - name: docker:20.10-dind
   before_script:
-    - docker login "https://${CI_REGISTRY}" -u $CI_REGISTRY_USER -p $CI_REGISTRY_PASSWORD
-    - docker pull $CI_REGISTRY_IMAGE:latest || true
+    - script/ci-docker-prebuild
   script:
-    # This enables fast parallel builds
-    - export DOCKER_BUILDKIT=1
-    - docker build --cache-from $CI_REGISTRY_IMAGE:latest -t $CI_REGISTRY_IMAGE:$CI_COMMIT_SHA .
-    # Push the commit SHA tagged version to registry. We will later choose to tag that as stable
-    #   if everything passes.
-    - docker push $CI_REGISTRY_IMAGE:$CI_COMMIT_SHA
+    - script/ci-docker-build
 
 # If tests pass, tag the commit and update package versions
 deploy_to_tags:
diff --git a/Dockerfile b/Dockerfile
index 12023f50..d9535972 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,4 +1,4 @@
-FROM elixir:1.10.4-alpine AS elixir1
+FROM elixir:1.10.4-alpine AS elixir-builder
 
 RUN mix local.hex --force \
   && mix local.rebar --force
@@ -37,7 +37,7 @@ COPY --from=0 /root/app/ /root/app/
 RUN npm install
 RUN npm run deploy
 
-FROM elixir1
+FROM elixir-builder
 
 RUN mix deps.compile
 
diff --git a/script/ci-docker-build b/script/ci-docker-build
new file mode 100755
index 00000000..0a80b6bd
--- /dev/null
+++ b/script/ci-docker-build
@@ -0,0 +1,27 @@
+#!/bin/sh
+
+export DOCKER_BUILDKIT=1
+
+docker build \
+  --target elixir-builder \
+  --cache-from $CI_REGISTRY_IMAGE:$PARENT_COMMIT-elixir-builder \
+  --cache-from $CI_REGISTRY_IMAGE:latest-elixir-builder \
+  -t $CI_REGISTRY_IMAGE:$CI_COMMIT_SHA-elixir-builder .
+
+docker build \
+  --target asset-builder \
+  --cache-from $CI_REGISTRY_IMAGE:$PARENT_COMMIT-asset-builder \
+  --cache-from $CI_REGISTRY_IMAGE:latest-asset-builder \
+  -t $CI_REGISTRY_IMAGE:$CI_COMMIT_SHA-asset-builder .
+
+docker build \
+  --target asset-builder \
+  --cache-from $CI_REGISTRY_IMAGE:$PARENT_COMMIT \
+  --cache-from $CI_REGISTRY_IMAGE:latest \
+  -t $CI_REGISTRY_IMAGE:$CI_COMMIT_SHA .
+
+# Push the commit SHA tagged version to registry. We will later choose to tag that as stable
+#   if everything passes.
+docker push $CI_REGISTRY_IMAGE:$CI_COMMIT_SHA-elixir-builder
+docker push $CI_REGISTRY_IMAGE:$CI_COMMIT_SHA-asset-builder
+docker push $CI_REGISTRY_IMAGE:$CI_COMMIT_SHA
diff --git a/script/ci-docker-prebuild b/script/ci-docker-prebuild
new file mode 100755
index 00000000..19c73c7d
--- /dev/null
+++ b/script/ci-docker-prebuild
@@ -0,0 +1,17 @@
+#!/bin/sh
+
+PARENT_COMMIT=`git rev-list --parents -n 1 HEAD  | cut -d' ' -f2`
+
+docker login "https://${CI_REGISTRY}" -u $CI_REGISTRY_USER -p $CI_REGISTRY_PASSWORD
+
+docker pull $CI_REGISTRY_IMAGE:$PARENT_COMMIT-elixir-builder || \
+  docker pull $CI_REGISTRY_IMAGE:latest-elixir-builder || \
+  true
+
+docker pull $CI_REGISTRY_IMAGE:$PARENT_COMMIT-asset-builder || \
+  docker pull $CI_REGISTRY_IMAGE:latest-asset-builder || \
+  true
+
+docker pull $CI_REGISTRY_IMAGE:$PARENT_COMMIT || \
+  docker pull $CI_REGISTRY_IMAGE:latest || \
+  true