Faster Docker Builds using Inline Caching

So you’re building a container where it has packages, like npm ci or go mod download, and would you like to make it quicker? For example:

COPY go.mod go.sum ./
RUN go mod download

Normally when you edit go.mod or go.sum the go mod download will have to redownload all the packages as its cache was busted by the change in the files.

Well - we can use inline bind mounts to avoid that.

These appear as --mount statements in the Dockerfile as part of RUN commands.

They instruct Docker to keep a cache, such as downloaded files, between different runs of docker build.

To use them add --mount=type=cache to your RUN command and specify a target.

COPY go.mod go.sum ./
RUN --mount=type=cache,target=/go/pkg/mod  \
	go mod download

Or for Node/NPM

RUN --mount=type=cache,target=/root/.npm npm install

Docs

Here are the Docker docks which go into more detail:

• 🚢 Docker Build: Using cache mounts

Mini Series

• Faster Docker Builds using Inline Caching
• Safer Docker Builds: Using Secrets to temporarily mount sensitive info
• Simpler docker-compose with inline config files