What file format does Docker Compose use to define services?

Docker Compose uses the YAML file format to define services, configurations, and dependencies of applications. YAML, which stands for "YAML Ain't Markup Language," is well-suited for configuration files due to its readability and simplicity. In the context of Docker Compose, it enables developers to create and manage multi-container Docker applications through a straightforward and human-readable structure. This format allows for an easy definition of various services, networks, and volumes within a single file, typically named docker-compose.yml.

The selection of YAML is particularly advantageous because it uses indentation to denote structure, making it clear and less error-prone compared to other formats that may be more rigid or less intuitive. The choice of YAML supports nested elements, which aligns perfectly with the hierarchical nature of service definitions in Docker Compose. This makes it a preferred format in the DevOps community for defining application environments.

While other formats like INI, JSON, and XML are used in various applications, they either do not offer the same level of readability or require more verbose syntax, which can make managing configurations less straightforward than using YAML in the Docker ecosystem.