Build Cache

Build Cache

Image builds can take some time

How it works

Images are made of layers defined by…

  1. Upstream layer
  2. Command executed

Build cache speeds up consecutive builds


Step 7/11 : ADD /
 ---> Using cache
 ---> a6b2bb261372

Demo: Build Cache

  1. First build
  2. Consecutive build
  3. Build after changes to Dockerfile

Build Cache Warming v1

Builds may not not run on the same host

How it works

Use local images to warm cache

docker pull myimage:1
docker build --cache-from myimage:1 --tag myimage:2

Internal build cache is ignored when using --cache-from


Added in Docker 1.13

Image must be present locally

Demo: Build Cache Warming v1

# Push image
docker run -d -p 5000:5000 registry:2
docker build --tag localhost:5000/hello-world-java .
docker push localhost:5000/hello-world-java

# Reset Docker
docker system prune --all

# Pull image
docker pull localhost:5000/hello-world-java

# Build with cache from local image
docker build --cache-from localhost:5000/hello-world-java .

Internal build cache is still used when cache image does not exist

Build Cache Warming v2

Large image downloads for few helpful layers

How it works

Use remote images to warm cache

Image layers will be downloaded as needed

Same syntax using --cache-from


Added in Docker 19.03

Demo: Build Cache Warming v2

Build with cache from remote image:

# Run Docker 19.03-rc
docker run -d --rm --name dind --privileged --network host \
    --volume $(pwd):/src --workdir /src docker:19.03-rc-dind
docker exec -it dind sh

# Run inside container
apk add --update-cache --no-cache curl jq
docker build --tag localhost:5000/test:1 \
    --build-arg BUILDKIT_INLINE_CACHE=1 .
docker push localhost:5000/test:1
docker system prune --all
docker build \
    --cache-from localhost:5000/test:1 .

Demo: Build Cache Warming v2

Check manifest for cache information:

curl -s \
    -H "Accept: application/vnd.docker.distribution.manifest.v2+json" \
    localhost:5000/v2/test/manifests/1 \
    | jq --raw-output '.config.digest' \
    | while read CONFIG_DIGEST; do \
        curl -s \
            -H "Accept: application/vnd.docker.container.image.v1+json" \
            localhost:5000/v2/test/blobs/${CONFIG_DIGEST} \
        | jq --raw-output '."moby.buildkit.cache.v0"' \
        | base64 -d \
        | jq; \