Module 5 Lesson 4: The Docker Compose CLI

Now that you have your docker-compose.yml file, you need to know how to interact with it. The docker-compose command (or docker compose in newer versions) is your control center.

1. The Core Lifecycle Commands

docker-compose up

Creates and starts all services in the file.

• -d: Detached mode (background).
• --build: Force a rebuild of all images before starting.

docker-compose down

Stops and Removes all containers, networks, and images defined in the file.

• -v: Also remove the Volumes (Be careful! This deletes your data).

docker-compose stop

Stops the containers but does not remove them.

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2. Monitoring and Debugging

docker-compose ps

Lists the status of all containers managed by the current Compose file.

docker-compose logs

Shows the aggregated output from every container in the stack.

• -f: Follow (stream) the logs in real-time.
• docker-compose logs web: Only show logs for the 'web' service.

docker-compose exec <service_name> <command>

Run a command inside a specific service.

• Example: docker-compose exec db psql -U postgres

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3. Modifying the Stack

If you change your docker-compose.yml file while the stack is running:

• Just run docker-compose up -d again.
• Docker Compose will detect which parts of the file changed and only recreate those specific containers. It leaves the unchanged ones running. (This is incredibly powerful for uptime!)

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4. Summary Table

Command	Action	Result
up -d	Start	Everything is running and linked
logs -f	Watch	See errors across the whole stack
stop	Pause	Everything is off, but state is kept
down	Destroy	Clean machine (no containers left)
build	Compile	Re-run the Dockerfiles

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Exercise: The Workflow Race

1. Run docker-compose up -d.
2. Make a small change to your nginx configuration (e.g., change the mapped port).
3. Run docker-compose up -d again. Note the output. Did it say "Recreating" or "Starting"?
4. Use docker-compose logs -f and then refresh your browser page. Do you see the logs appearing in your terminal?
5. What happens to your volumes if you run docker-compose down? What about docker-compose down -v?

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Summary

The Compose CLI is tailored for managing groups of containers. By mastering up, down, and logs, you gain total visibility into the complex web of interactions that make up a modern multi-service application.

Next Lesson: Putting it all together: A real-world multi-container application example.