Your starter guide to Docker troubleshooting

Some common Docker troubleshooting commands:

docker ps -a: Lists all containers, including stopped ones. This can be useful to see if a container that should be running is actually stopped.

docker logs [container-name]: View the logs of a container. This can be useful to see if there are any error messages or issues with the application running inside the container.

docker inspect [container-name/image-name]: View detailed information about a container or image, such as its configurations, network settings, and exposed ports. This can be useful to see if there are any issues with the container's settings.

docker events: View real-time events from the Docker daemon. This can be useful to see what actions are being performed on the Docker host, such asstarting or stopping containers.

docker stats: View real-time performance statistics for running containers. This can be useful to see if there are any performance issues with a container, such as high CPU or memory usage.

docker system prune: Remove all stopped containers, all networks not used by at least one container, all dangling images, and all build cache. This can be useful to clean up resources and free up disk space on the Docker host.

docker system df: Show disk usage of the Docker host. This can be useful to see if there are any disk space issues on the host.

docker exec -it [container-name] /bin/bash: Open a bash session inside a running container. This can be useful to troubleshoot issues inside the container, such as checking the configuration files or running commands.

docker container ls -f status=exited: Lists all containers with status 'exited'

These commands can help you to troubleshoot and diagnose issues with running containers and images, but they are not exhaustive, and depending on the specific problem you might need to use other commands or consult the official Docker documentation for more information.

Some common troubleshooting steps for Docker networks:

Verify that the network is created: Use the command docker network ls to list all networks and ensure that the network in question is present.

Check the network settings: Use the command docker network inspect [network-name] to view detailed information about the network, including its configurations and settings.

Verify that the container is connected to the network: Use the command docker container inspect [container-name] to view detailed information about the container, including its network settings. Ensure that the container is connected to the correct network.

Check the container's IP address: Use the command docker container inspect --format '{{ .NetworkSettings.IPAddress }}' [container-name] to view the container's IP address. Ensure that the IP address is within the expected range for the network.

Check the container's DNS settings: Use the command docker container inspect --format '{{ .NetworkSettings.Networks.network-name.IPAddress }}' [container-name] to view the container's DNS settings. Ensure that the DNS settings are correct and match the network's settings.

Check the container's port mapping: Use the command docker container inspect --format '{{ .NetworkSettings.Ports }}' [container-name] to view the container's port mapping. Ensure that the ports are mapped correctly and match the network's settings.

Check for iptables rules: Use the command sudo iptables -L to check for any iptables rules that might be blocking network access.

Restart the container: If all the above steps have been checked and the issue persist, try restarting the container with the command docker restart [container-name].

Check the container logs: Use the command docker logs [container-name] to check if the container has any error messages or issues with the network.

Check the host's network settings: If the issue persists, verify that the host's network settings are configured correctly.

Ways to inspect Docker logs:

To check the logs of a running Docker container, you can use the docker logs command followed by the container name or container ID.

For example:

docker logs [container-name]

or

docker logs [container-id]

By default, the docker logs command shows the logs of the container in the standard output (stdout) and the standard error (stderr). If you want to see only the stdout or stderr logs, you can use the --tail option, and define how many lines of logs you want to see, like

docker logs --tail 20 [container-name]

This will display the last 20 lines of logs.

You can also use the -f or --follow option to stream the logs in real-time. For example:

docker logs -f [container-name]

Additionally, you can use the -t option to prefix each log line with the timestamp.

docker logs -t [container-name]

It is also worth noting that by default, logs are stored in a json file and rotated by size, this rotation is controlled by the json-file log driver. You can change the log driver to other like syslog or journald using the --log-driver option at container creation.

These troubleshooting steps can help you to diagnose and resolve issues with Docker Platform.