Make Docker-in-Docker builds faster with Docker layer caching
When using Docker-in-Docker, Docker downloads all layers of your image every
time you create a build. Recent versions of Docker (Docker 1.13 and later) can
use a pre-existing image as a cache during the
docker build step. This significantly
accelerates the build process.
How Docker caching works
docker build, each command in
Dockerfile creates a layer.
These layers are retained as a cache and can be reused if there have been no changes. Change in one layer causes the recreation of all subsequent layers.
To specify a tagged image to be used as a cache source for the
command, use the
--cache-from argument. Multiple images can be specified
as a cache source by using multiple
--cache-from arguments. Any image that’s used
--cache-from argument must be pulled
docker pull) before it can be used as a cache source.
Docker caching example
.gitlab-ci.yml file shows how to use Docker caching:
image: docker:20.10.16 services: - docker:20.10.16-dind variables: # Use TLS https://docs.gitlab.com/ee/ci/docker/using_docker_build.html#tls-enabled DOCKER_HOST: tcp://docker:2376 DOCKER_TLS_CERTDIR: "/certs" before_script: - docker login -u $CI_REGISTRY_USER -p $CI_REGISTRY_PASSWORD $CI_REGISTRY build: stage: build script: - docker pull $CI_REGISTRY_IMAGE:latest || true - docker build --cache-from $CI_REGISTRY_IMAGE:latest --tag $CI_REGISTRY_IMAGE:$CI_COMMIT_SHA --tag $CI_REGISTRY_IMAGE:latest . - docker push $CI_REGISTRY_IMAGE:$CI_COMMIT_SHA - docker push $CI_REGISTRY_IMAGE:latest
script section for the
- The first command tries to pull the image from the registry so that it can be
used as a cache for the
- The second command builds a Docker image by using the pulled image as a
cache (see the
--cache-from $CI_REGISTRY_IMAGE:latestargument) if available, and tags it.
- The last two commands push the tagged Docker images to the container registry so that they can also be used as cache for subsequent builds.