How to Check Docker Logs?
Troubleshooting Docker Container Logs - When utilizing Docker containers, logging is an important aspect of monitoring and troubleshooting. Container logs provide informative information about the container's behavior, supporting you in problem-solving and validating that your container is running as it should. However, container logs may not always be accessible or deliver the appropriate information. In this post, we'll look at some common causes of this issue and suggest some solutions to help you tackle it.
You May also like this: Docker Desktop Alternatives
Understanding Docker Logging
Let's take a quick look at how Docker logging functions before we get started with troubleshooting. Stderr, Stdout, and Syslog are the three types of logs that Docker by default collects. These logs are gathered and kept in JSON format on the host system. These logs may be viewed using the docker logs command or sent to an external system for additional analysis using a logging driver.
Docker builds a fresh logging driver for each container it starts. JSON-file, the default driver, outputs container logs in JSON format to disc. If you'd rather, you may set up Docker to utilise a different logging driver. Syslog, journald, splunk, and fluentd are a few examples of well-liked logging drivers.
Common Causes of Missing or Incomplete Container Logs
Let us now look at some of the typical causes of missing or inaccurate output from container logs..
1. Logging Driver Misconfiguration
A poorly configured logging driver is one potential reason why container logs are absent or not complete. Docker might not be able to capture the container's logs if the logging driver is not configured properly. You may use the docker info command to examine your logging driver setup by looking for the Logging Driver column. You might need to alter your Docker daemon settings if this field is empty or set to an unexpected value.
2. Insufficient Disk Space
Insufficient disc space on the host system is another potential reason why container logs are missing or incomplete. Docker may be unable to write fresh logs to disc if the disc capacity is running low, leading to missing or truncated logs. You may use the "df -h" command on the host system to view your disc space use. You might need to delete unwanted files or resize the disc to free up some space if the disc space use is excessive.
3. Container Restart
docker run --log-driver json-file --log-opt max-size=100m --log-opt max-file=10 myimage
4. Logging Driver Failure
For instance, Docker might not be able to write the logs to the syslog if the syslog driver is unable to connect to the syslog daemon. Critical log data may be lost as a result or may not be captured, which can make it difficult to locate and fix problems.
5. Application Configuration Issues
Sometimes difficulties with the application's set up or programming can result in missing or insufficient logs. For instance, Docker might not be able to collect the logs if an application is not set up to log to stdout or stderr. You may require to change the application's configuration or the source code to log to stderr or stdout in order to fix this problem.
Troubleshooting Missing or Incomplete Container Logs
After identifying some of the common causes for missing or insufficient container logs, we'll look at certain methods for troubleshooting you can apply to fix the problem..
1. Check Logging Driver Configuration
Checking the setup of the logging driver is the first step in troubleshooting missing or insufficient container logs. Run the "docker info" command and check for the Logging Driver column to accomplish this. It's possible that you need to adjust your Docker daemon settings if the field is blank or set to an unexpected value.
2. Check Disk Space Usage
The next action is to examine the host machine's disc space utilisation if the logging driver setup is correct. To accomplish this, issue the "df -h" command. You might need to delete unwanted files or resize the disc to free up some space if the disc space use is excessive.
Download Free Linux Commands Cheat sheet!
3. Check Container Restart Frequency
If the use of disc space is not the problem, you should look at the frequency of container restarts. Docker might not be able to collect the logs if the container restarts often. Using the" --log-opt max-size" and "--log-opt max-file" options, you may instruct Docker to append new logs to the current logs in order to avoid this from happening.
For example, the following command limits the log files to 100MB in size and keeps a maximum of 10 log files:
docker run --log-driver json-file --log-opt max-size=100m --log-opt max-file=10 myimage4. Check Logging Driver Failure
You should check to see if the logging driver is operating properly if the preceding procedures did not address the problem. Run the "docker logs" command and scan it for any error messages to accomplish this. You might need to debug the logging driver or change to a new logging driver if it isn't operating properly.
5. Check Application Configuration
If none of the above actions were successful, you should verify the application configuration. Make sure the application is set up to output logs to stderr or stdout. To determine if the problem still exists, you may also attempt to execute the application without using Docker.
Conclusion
An crucial tool for problem-solving in a containerized system is the container log. However, missing or imperfect container logs can be annoying and challenging to fix. In this post, we've covered a few of the usual reasons why container logs go missing or are only partially full, as well as some troubleshooting techniques to help you fix the problem.
When troubleshooting missing or incomplete container logs, always remember to look at your logging driver setup, disc space consumption, container restart frequency, logging driver failure, and application configuration. You can detect and fix problems with container logs fast and effectively using these suggestions.
RELATED ARTICLES: Docker Desktop Alternative
thanks for Linux Commands Cheat sheet!
ReplyDelete