Logs
Logs show detailed events, errors, and startup behavior so you can understand what happened inside the container.
Lesson 23
Monitoring and logs
This page explains why running containers are only useful when you can also see what they are doing over time.
Monitoring
Monitoring shows higher-level health such as uptime, memory use, CPU pressure, and error trends over time.
Main lesson
A deployed container is not truly manageable if you cannot inspect its behavior when something goes wrong.
Logs answer
What happened?
What error appeared?
What did startup say?
Monitoring answers
Is it up?
Is it slowing down?
Is resource usage rising?
Why logs matter first
- They help explain crashes and startup failures.
- They reveal missing config or connection issues.
- They are often the first debugging tool after deployment.
- They make post-deployment troubleshooting faster.
Why monitoring matters next
- It helps you detect slowdowns before users complain.
- It highlights unhealthy behavior patterns over time.
- It gives confidence that the system is still stable.
- It supports scaling and capacity decisions later.
Practical Docker command examples
docker logs <container_id>
docker compose logs
docker ps
docker inspect <container_id>
These commands help you answer simple but important runtime questions quickly.
Common beginner mistake
Seeing `running` in `docker ps` and assuming everything is fine. A container can be running while the application is still unhealthy or misbehaving.
Observation mindset
Deploy
The service starts.
The service starts.
Observe
Logs show what it is doing.
Logs show what it is doing.
Measure
Monitoring shows whether it remains healthy over time.
Monitoring shows whether it remains healthy over time.
Improve
Now you can make better decisions using real signals instead of guesses.
Now you can make better decisions using real signals instead of guesses.
Next page: Lesson 24 explores more structured Docker Compose patterns for larger projects.