From 611204c38246215ec5f6e8681874f7abb9cdb8cc Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?R=C3=A9my=20Coutable?= <remy@rymai.me>
Date: Tue, 25 Feb 2020 19:06:49 +0100
Subject: [PATCH] Only build/tag/push images once
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Content-Transfer-Encoding: 8bit

Signed-off-by: Rémy Coutable <remy@rymai.me>
---
 .gitlab-ci.yml              | 17 ++++++++++++++---
 README.md                   | 12 ++++++++++++
 scripts/build-helpers.sh    | 25 +++++++++++++++++++++++++
 scripts/custom-docker-build | 27 ++++++++++++++++++++++-----
 4 files changed, 73 insertions(+), 8 deletions(-)
 create mode 100644 scripts/build-helpers.sh

diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 40172d2..105bcbe 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -6,13 +6,16 @@ stages:
   - automation
 
 services:
-- docker:dind
+  - docker:19.03.0-dind
 
 variables:
-  DOCKER_DRIVER: overlay
+  DOCKER_DRIVER: overlay2
+  DOCKER_HOST: tcp://docker:2375
+  FORCE_BUILD: "false"
 
 before_script:
   - docker login -u "gitlab-ci-token" -p "$CI_JOB_TOKEN" "$CI_REGISTRY"
+  - source scripts/build-helpers.sh
 
 .test_build: &test_build
   stage: test
@@ -23,6 +26,8 @@ before_script:
     - docker build -f "Dockerfile.$1" .
   except:
     - master
+  tags:
+    - docker
 
 .build_and_deploy: &build_and_deploy
   stage: build
@@ -31,6 +36,8 @@ before_script:
     - docker push "$CI_REGISTRY_IMAGE:$CI_JOB_NAME"
   only:
     - master
+  tags:
+    - docker
 
 .test_custom: &test_custom
   stage: test
@@ -41,14 +48,18 @@ before_script:
     - ./scripts/custom-docker-build $1
   except:
     - master
+  tags:
+    - docker
 
 .build_and_deploy_custom: &build_and_deploy_custom
   stage: build
   script:
     - ./scripts/custom-docker-build $CI_JOB_NAME -t "$CI_REGISTRY_IMAGE:$CI_JOB_NAME"
-    - docker push "$CI_REGISTRY_IMAGE:$CI_JOB_NAME"
+    - push_if_needed "$CI_REGISTRY_IMAGE:$CI_JOB_NAME"
   only:
     - master
+  tags:
+    - docker
 
 # Tests
 
diff --git a/README.md b/README.md
index 9e2b415..67c534c 100644
--- a/README.md
+++ b/README.md
@@ -65,6 +65,18 @@ the name would be `ruby-2.4-golang-1.9-git-2.14`.
 1. Add a test task: `ruby-2.4-golang-1.9-git-2.14 test: *test_custom`
 1. Add a new build task: `ruby-2.4-golang-1.9-git-2.14: *build_and_deploy_custom`
 
+#### Forcing custom images to be rebuilt
+
+By default, once a custom image is built, tagged and pushed to the registry, it's
+not rebuilt to ensure an upstream dependency doesn't end up breaking our images
+unexpectedly.
+
+For reference, this happened in the past: https://gitlab.com/gitlab-org/gitlab/issues/205192
+
+In the rare case where the `Dockerfile.custom` file is updated and all custom
+images shoulld be rebuild, you can start a new pipeline and set the variable
+`FORCE_BUILD` to `true`.
+
 ## Note regarding Google Chrome
 
 Google has a policy of yanking older versions of Google Chrome from their PPA
diff --git a/scripts/build-helpers.sh b/scripts/build-helpers.sh
new file mode 100644
index 0000000..52b25b0
--- /dev/null
+++ b/scripts/build-helpers.sh
@@ -0,0 +1,25 @@
+function image_already_exists() {
+    image=$1
+
+    $(docker pull $image > /dev/null)
+}
+
+function build_if_needed() {
+    image=$1
+
+    if ! image_already_exists $image; then
+        docker build -t "$image" -f "Dockerfile.$image" .
+    else
+        echo "$image already exists, skipping build."
+    fi
+}
+
+function push_if_needed() {
+    image=$1
+
+    if ! image_already_exists $image; then
+        docker push "$image"
+    else
+        echo "$image already exists, skipping push."
+    fi
+}
diff --git a/scripts/custom-docker-build b/scripts/custom-docker-build
index d6a5c05..99e4b0e 100755
--- a/scripts/custom-docker-build
+++ b/scripts/custom-docker-build
@@ -3,6 +3,8 @@
 set -e
 IFS=$'\n\t'
 
+source scripts/build-helpers.sh
+
 function print_golang_args() {
 
     case "$1" in
@@ -198,10 +200,10 @@ function parse_arguments() {
 }
 
 function generate_command() {
-    buildimage_name=$1; shift;
+    build_image_name=$1; shift;
 
     printf -- "docker build "
-    echo $buildimage_name | tr '-' '\n' | parse_arguments
+    echo $build_image_name | tr '-' '\n' | parse_arguments
 
     for i in "$@"
     do
@@ -210,6 +212,21 @@ function generate_command() {
     printf -- ".\\n"
 }
 
-docker_command=$(generate_command $@)
-echo "$1: executing $docker_command"
-eval $docker_command
+function build_custom_if_needed() {
+    build_image_name=$1
+    full_image_name="$CI_REGISTRY_IMAGE:$build_image_name"
+
+    if [[ "$FORCE_BUILD" == "true" ]] || ! image_already_exists $full_image_name; then
+      docker_command=$(generate_command $@)
+      if [[ "$FORCE_BUILD" == "true" ]]; then
+        echo "Force building $build_image_name due to `\$FORCE_BUILD=true` with $docker_command"
+      else
+        echo "Building $build_image_name with $docker_command"
+      fi
+      eval $docker_command
+    else
+      echo "$build_image_name already exists, skipping build."
+    fi
+}
+
+build_custom_if_needed $@