Docker Compose Orchestration

Overview

Docker Compose simplifies the management of multi-container applications. It enables service discovery through internal hostnames and provides mechanisms for environment-specific configurations using profiles.

When to Use

• Local Development: Spinning up a full stack (frontend, backend, DB) with one command.
• CI/CD Integration: Running isolated integration tests in containerized environments.
• Microservices: Orchestrating communication between multiple independent services.

Decision Tree

1. Do you have services only needed for debugging?
   • YES: Use profiles to keep them optional.
2. Do you need to hide a database from the public proxy?
   • YES: Create isolated custom networks.
3. Do you need to connect to a service outside the current YAML file?
   • YES: Use external: true for that network.

Workflows

1. Isolating Internal Services

1. Define frontend and backend custom networks in the top-level networks key.
2. Assign the proxy service to the frontend network.
3. Assign the app service to both frontend and backend.
4. Assign the db service only to the backend network to isolate it from the proxy.

2. Environment-Specific Overrides with Profiles

1. Add profiles: [debug] to an optional service (e.g., phpmyadmin) in compose.yaml.
2. Run docker compose up for standard operations; debug services stay off.
3. Run docker compose --profile debug up to include the debugging tools.

3. Using Existing External Networks

1. Declare a network in compose.yaml with external: true.
2. Link local services to this external network in their networks section.
3. This allows the Compose stack to communicate with containers managed outside the current project.

Non-Obvious Insights

• Service Name as Hostname: Within the default network, you don't need IPs; containers connect via service names (e.g., db:5432).
• IP Persistence: Configurations changes cause containers to get new IPs, but the hostname (service name) remains consistent, which is why service discovery is essential.
• Implicit Enablement: Services without a profiles attribute are always enabled regardless of which profiles are requested.

Evidence

• "Each container for a service joins the default network and is... discoverable by the service's name." - Docker Docs
• "Profiles help you adjust your Compose application for different environments... by selectively activating services." - Docker Docs
• "Instead of just using the default app network, you can specify your own networks..." - Docker Docs

Scripts

• scripts/docker-compose_tool.py: Python script to generate dynamic Compose YAML files.
• scripts/docker-compose_tool.js: Node.js script for checking service connectivity within a network.

Dependencies

• docker-compose
• docker engine

References

• references/README.md