When encountering Docker problems, you should first locate the problem, which is problems such as image construction, container operation or network configuration, and then follow the steps to check. 1. Check the container logs (docker logs or docker-compose logs) for error information; 2. Check the container status (docker ps) and resource usage (docker stats) to determine whether there is an exception due to insufficient memory or port problems; 3. Enter the inside of the container (docker exec) to verify paths, permissions and dependencies; 4. Review whether there are configuration errors in the Dockerfile and compose files, such as environment variable spelling or volume mount path problems, and recommend that clean build avoid cache interference. Follow these procedures to solve most common problems.

Don't panic when encountering Docker problems, first figure out where the problem is. Docker is not a black box, and many common problems actually have rules to follow. The key is to be able to locate the source of the problem: is it a mirror construction, container operation, or is there a problem with the network configuration? The following directions can basically cover most investigation scenarios.

Viewing container logs is the most direct way

When you feel that the container is not working as expected, the first reaction should be to see what it outputs. Use docker logs [容器ID] to see standard output and standard error information, and often the cause of the error is written in it.

for example:

• Start script error
• Port occupied
• Configuration file failed to load

If you use docker-compose , the command can be simplified into docker-compose logs [服務(wù)名] , which is more convenient to track the situation of multiple services.

Small suggestions: If there are too many logs, you can use the --tail parameter to view only the last few lines, or add -f to track the output in real time.

Check container status and resource usage

Sometimes the container seems to be "stuck", but it actually runs normally but has no output. At this time, use docker ps to see if the container is in the running state (UP), and whether its port mapping is correct.

You can also use docker stats to view the real-time resource usage of CPU, memory, network, etc., which is very helpful in troubleshooting performance bottlenecks.

Frequently asked questions include:

• Exit immediately after the container is started (exit code is not 0)
• Out of memory causes OOMKilled
• The network is not connected and the external or host cannot be accessed

Don't rush to restart at this time, look at the status first and then analyze it.

Enter the container to check the environment

Some problems are exposed only when running, such as wrong paths, insufficient permissions, and lack of dependencies. You can use docker exec -it [容器ID] sh or bash (depending on the underlying image) to enter the container and manually execute the command verification logic.

For example:

 docker exec -it my_container ls /app/logs
docker exec -it my_container curl http://localhost:3000

This can directly verify whether the application is really listening to a certain port, or whether the file is correctly mounted.

Note: Some minimalist images (such as scratch-based) may not even have shells, and in this case, they can only rely on logs or other tools to troubleshoot.

Review Dockerfile and compose file configurations

Many problems were actually buried at the beginning, such as:

• The basic mirror version is too old
• CMD/ENTRYPOINT is written wrong
• The volume mount path is written inversely
• Error spelling of environment variables

Especially in multi-person collaboration projects, it is easy to make mistakes when modifying configuration files. It is recommended to do a clean build every time the configuration is modified to avoid cache interference.

Basically these steps. To troubleshoot Docker problems, you don’t need to have very advanced technology. The key is to follow the process step by step, without jumping or guessing. Many "magic" bugs are actually just spelling errors or paths written in reverse.

The above is the detailed content of How to troubleshoot Docker issues. For more information, please follow other related articles on the PHP Chinese website!