Optimize Docker Offload usage

Docker Offload runs your builds remotely, not on the machine where you invoke the build. This means that files must be transferred from your local system to the cloud over the network.

Transferring files over the network introduces higher latency and lower bandwidth compared to local transfers. To reduce these effects, Docker Offload includes several performance optimizations:

• It uses attached storage volumes for build cache, which makes reading and writing cache fast.
• When pulling build results back to your local machine, it only transfers layers that changed since the previous build.

Even with these optimizations, large projects or slower network connections can lead to longer transfer times. Here are several ways to optimize your build setup for Docker Offload:

• Use .dockerignore files
• Choose slim base images
• Use multi-stage builds
• Fetch remote files during the build
• Leverage multi-threaded tools

For general Dockerfile tips, see Building best practices.

dockerignore files

A .dockerignore file lets you specify which local files should not be included in the build context. Files excluded by these patterns won’t be uploaded to Docker Offload during a build.

Typical items to ignore:

• .git – avoids transferring your version history. (Note: you won’t be able to run git commands in the build.)
• Build artifacts or locally generated binaries.
• Dependency folders such as node_modules, if those are restored in the build process.

As a rule of thumb, your .dockerignore should be similar to your .gitignore.

Slim base images

Smaller base images in your FROM instructions can reduce final image size and improve build performance. The alpine image is a good example of a minimal base.

For fully static binaries, you can use scratch, which is an empty base image.

Multi-stage builds

Multi-stage builds let you separate build-time and runtime environments in your Dockerfile. This not only reduces the size of the final image but also allows for parallel stage execution during the build.

Use COPY --from to copy files from earlier stages or external images. This approach helps minimize unnecessary layers and reduce final image size.

Fetch remote files in build

When possible, download large files from the internet during the build itself instead of bundling them in your local context. This avoids network transfer from your client to Docker Offload.

You can do this using:

• The Dockerfile ADD instruction
• RUN commands like wget, curl, or rsync

Multi-threaded tools

Some build tools, such as make, are single-threaded by default. If the tool supports it, configure it to run in parallel. For example, use make --jobs=4 to run four jobs simultaneously.

Taking advantage of available CPU resources in the cloud can significantly improve build time.