Docker Best Practices: Reduce Errors by 30% with Smarter Compose Files

It may seem quite strange due to the way it's done, but there's a way to avoid rework when writing a docker-compose.yml.

There are two structures that help reduce rework:

• Extensions (x-): Allow defining reusable custom configurations, such as variables, networks, or volumes, without cluttering the main structure of docker-compose.yml.
• Anchors (& and *): Facilitate the reuse of configuration snippets, avoiding duplication and ensuring consistency across services.

As you can see in the image below, an extension allows you to reuse directives in other services.

To create an extension in a Docker Compose file, simply start the directive at the top of the file with "x-".

It will look something like: "x-common-values" or "x-values".

Then, define it using an ampersand (&) followed by a name:

Example: "x-common-values: &common-values"

The x-common-config extension is used to define shared settings like restart policy and network configuration. By referencing <<: *common-config, the app, database, and cache containers all inherit these common settings, keeping the docker-compose.yml clean and consistent. This reduces repetition and makes updates easier.

After creating the extension, to use it within a service, just insert the instruction followed by

"<<: *" the extension name.

It will look like this: "<<: *common-values".

And voilà!

Your docker-compose.yml file will now be more concise, readable, and require less rework.

If you ever need to make a change, you’ll only have to update it in one place!

And you? Have you ever used extensions in your Docker Compose files? ??