Docker can't find it in the log

Docker is a popular containerization technology that can run multiple applications on a single host. However, you may encounter some problems when using Docker, such as checking the logs of a running container but finding no records. This question may confuse you because the running of the container will inevitably generate logging.

So, why may you encounter the problem of not being able to find the log when viewing the log in Docker? This article will explain and discuss the following aspects.

1. Docker’s log driver

The logging driver used by Docker is very important because it can affect logging and viewing. By default, Docker uses the json-file driver, which writes the container's standard output and standard error output into JSON files and stores them in the /var/lib/docker/containers/ directory of the Docker host.

If you use other log drivers, such as syslog or journald, then you need to pay attention to the characteristics and usage of these log drivers. When using a non-default log driver, you need to confirm whether the logs allowed by the driver are recorded correctly. Otherwise, you may run into problems finding logs.

2. Log levels and logging format

In Docker, logs can be classified according to different log levels. By default, Docker will record logs at INFO level and above. If the log level you are using is DEBUG or lower, then you need to check whether the logging format in Docker is set correctly for your log configuration.

Therefore, you need to determine what log levels and logging formats your application is using, and check whether Docker's logging driver is compatible with them. If it's inconsistent, you'll need to adjust it to the same level and format as Docker's logging driver.

3. Container environment issues

When you run a container, the environment of the container itself may affect logging and viewing. For example, depending on the configuration of the container itself, it may read standard output or standard error to a different location than the default location of the Docker log drive.

In addition, there may be some container environment problems, such as the container not setting file permissions correctly or the container's storage space being full. These container environment issues can affect logging and viewing.

4. Limitations of Docker logging

Finally, it needs to be mentioned that Docker’s logging also has certain limitations. For example, Docker only logs the standard output and standard error output of the container by default, excluding other logs inside the container. Additionally, logging before the container is started or after the container is stopped may result in incomplete logging.

Therefore, if you need more comprehensive logging, you may need to use a third-party log collection tool, such as ELK, Fluentd or Splunk, etc., to achieve more comprehensive logging and visualization.

Summary

Docker is a popular containerization technology that provides multiple ways to view the running logs of containers. When viewing logs in Docker, you need to pay attention to Docker's log driver, log level and logging format, container environment issues, and limitations of Docker logging. By carefully examining these aspects, you can more effectively find and resolve logging issues in Docker. At the same time, you also need to regard logs as an important part of improving the stability and security of container applications, and incorporate their configuration and monitoring into your container management plan at any time.

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