What is Docker Compose and why it is used for multi-container applications.
Docker Compose is a powerful tool for defining and running multi-container Docker applications. While you can manually create networks and run individual containers to build a multi-service application, this process is cumbersome, error-prone, and not easily repeatable. Docker Compose addresses this by allowing you to use a simple YAML file, typically named `docker-compose.yml`, to configure your application's services, networks, and volumes. Within this single file, you can define everything needed to run your application. For example, you can specify a 'web' service that builds from a Dockerfile, a 'db' service that uses a public PostgreSQL image, and a 'redis' service for caching. You can define how they connect by placing them on a custom network, and you can specify volumes to persist database data. Once this file is defined, you can use a single command, `docker-compose up`, to create and start all the services from your configuration. This declarative 'infrastructure-as-code' approach makes your application setup predictable, versionable, and easily shareable among team members. It's the standard tool for local development, testing, and even some small-scale production deployments of multi-service applications.