Reducing build times with Multi Stage builds and yum caching

As a Build Engineer I'm always looking for ways to make builds faster, reduce dependencies, reduce waste and increase resilience.

This is just a quick example of re-using a local cache of yum packages during build time.

This will also work for Advanced Package Tool (apt) and Alpine Package Manager (apk).

Benefits

• Reduces build time
• Offline installs
• Less bandwidth used
• Better protection against network "flaps" at build time

Create a cache image

Create a container image that contains a cache of yum packages.

This command will create a container image which is Alpine based and includes the Centos7 Development Tools and dependencies.

docker build -t devtools:latest -f Dockerfile.createcache .

Build developer environment without using the cache

The following command will build a container image which downloads and installs the Centos7 Development Tools and dependencies.

time docker build -t devenv:latest -f Dockerfile.dev_env .

This will take a few minutes to download and install the Centos7 Development Tools and dependencies.

Build developer environment using the cache

Uncomment lines 6 and 10 and run :

time docker build -t devenv:latest -f Dockerfile.dev_env .

This build will re-use the packages cached in the devtools:latest image so you should see a much faster build time.

Summary

There are lot's of little use cases (and some big) for Multi Stage builds in Docker 17.05 and this is just one of them.

@tomwillfixit @shipitcon