Computer programs (software) sometimes fail to behave as expected. This is due to faulty code or due to the environmental changes between the development, testing, and deployment systems. Docker container technology eliminates the environmental issues between development, testing, and deployment as much as possible by containerizing all the application dependencies. Nonetheless, there could be still anomalies due to faulty code or variations in the kernel behavior, which needs debugging. Debugging is one of the most complex processes in the software engineering world and it becomes much more complex in the container paradigm because of the isolation techniques. In this section, we are going to learn a few tips and tricks to debug a containerized application using the tools native to Docker, as well as the tools provided by external sources.

Initially, many people in the Docker community individually developed their own debugging tools, but later Docker started supporting native tools, such as exec, top, logs, and events. In this section, we will dive deep into the following Docker tools:

• exec
• ps
• top
• stats
• events
• logs
• attach

We shall also consider debugging a Dockerfile.