Status of the specification

Note

This page contains information for developers who wish to implement or extend Compose within their product or tool. It contains basic usage requirements and expected behavior.

This document specifies the Compose file format used to define multi-containers applications. Distribution of this document is unlimited.

The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “MAY”, and “OPTIONAL” in this document are to be interpreted as described in RFC 2119.

Requirements and optional attributes

The Compose specification includes properties designed to target a local OCI container runtime, exposing Linux kernel specific configuration options, but also some Windows container specific properties. It is also designed for cloud platform features related to resource placement on a cluster, replicated application distribution, and scalability.

We acknowledge that no Compose implementation is expected to support all attributes, and that support for some properties is platform dependent and can only be confirmed at runtime. The definition of a versioned schema to control the supported properties in a Compose file, established by the docker-compose tool where the Compose file format was designed, doesn’t offer any guarantee to the end-user that attributes will be actually implemented.

The specification defines the expected configuration syntax and behavior. Unless noted, supporting any of these is OPTIONAL.

A Compose implementation to parse a Compose file using unsupported attributes SHOULD warn users. We recommend the following implementors to support those running modes:

• Default: warn the user about unsupported attributes, but ignore them
• Strict: warn the user about unsupported attributes and reject the Compose file
• Loose: ignore unsupported attributes AND unknown attributes (that were not defined by the spec by the time implementation was created)