Build & Cache multi-stage Docker images (with Build Specification for AWS CodeBuild)

01-multistage-build.sh

# the general idea
ImageTag="git"
FilePath="/Dockerfile"
RepoURI="123456789012.dkr.ecr.eu-west-1.amazonaws.com/repo"
Stages=$(cat $FilePath | grep -oP '^FROM .+ (AS|as) \K(.+)$')
CacheArgs=$(for Stage in $Stages; do echo "--cache-from $RepoURI:cache-$Stage"; done | paste -sd ' ')
BuildArgs="--file $FilePath $CacheArgs"
for Stage in $Stages; do docker pull $RepoURI:cache-$Stage || true; done
for Stage in $Stages; do docker build $BuildArgs --tag $RepoURI:cache-$Stage --target $Stage . || break; done
docker build $BuildArgs --tag $RepoURI:$ImageTag .
docker push $RepoURI:$ImageTag
docker tag $RepoURI:$ImageTag $RepoURI:latest
docker push $RepoURI:latest
for Stage in $Stages; do docker push $RepoURI:cache-$Stage || true; done

02-multistage-buildspec.yaml

version: 0.2
phases:
  pre_build:
    commands:
      - ImageTag=$(echo $CODEBUILD_BUILD_ID | sed 's/[^A-Za-z0-9]/-/g')
      - Stages=$(cat $FilePath | grep -oP '^FROM .+ (AS|as) \K(.+)$')
      - CacheArgs=$(for Stage in $Stages; do echo "--cache-from $RepoURI:cache-$Stage"; done | paste -sd ' ')
      - BuildArgs="--file $FilePath $CacheArgs"
      - $(aws ecr get-login --no-include-email)
      - for Stage in $Stages; do docker pull $RepoURI:cache-$Stage || true; done
  build:
    commands:
      - for Stage in $Stages; do docker build $BuildArgs --tag $RepoURI:cache-$Stage --target $Stage . || break; done
      - docker build $BuildArgs --tag $RepoURI:$ImageTag .
      - docker tag $RepoURI:$ImageTag $RepoURI:latest
  post_build:
    commands:
      - |
        if [ $CODEBUILD_BUILD_SUCCEEDING = 1 ]; then
          docker push $RepoURI:$ImageTag
          docker push $RepoURI:latest
          for Stage in $Stages; do docker push $RepoURI:cache-$Stage || true; done
        fi