Troubleshoot containerized applications

Understand the description of application resources

Understanding the description of application resources involves leveraging a number of podman commands.

Basic container inspection can be done with podman inspect [container_name_or_id] from this we can get

• ID
• Args
• Image
• Pod
• Volume
• Network

Get application logs

podman logs container_name_or_id] if the container writes to stdout / stderr. Otherwise it may log to a file or directly to an external logging aggregator

Inspect running applications

podman inspect can also be used to accomplish this. IE to identify any exposed ports.

Health checks can be run by executing podman healthcheck run [container_name_or_id]. Note, this requires health checks to be configured on the container. An example of which can be defined in the compose file:

healthcheck:
  test: ["CMD", "curl", "-f", "http://localhost"]
  interval: 1m30s
  timeout: 10s
  retries: 3
  start_period: 2m

Changes to the containers filesystem can be identified with podman diff [container_name_or_id]

Connecting to running containers

podman exec -it [container_name_or_id] /bin/sh (change sh to an appropriate shell). This will create a interactive shell directly inside the container subsequent commands can be run.

If we know exactly what we need to run in the container and log the output to stdout, we can use

podman exec [container_name_or_id] [command]

For example:

podman exec [container_name_or_id] ls /path/to/directory

We can also specify a specific user to run the command as, using the user flag:

podman exec --user [username] [container_name_or_id] [command]