Explore Docker's system logs

Docker is a lightweight virtualization technology that can isolate applications in independent containers and allow applications to run in different environments, thereby achieving rapid deployment and portability of applications. In the Docker container life cycle, the system log is a very important link. It can help us monitor and maintain the status of the container to ensure the normal operation of the container. So, what is Docker’s system log? How to use and configure Docker's system log? This article will introduce you to Docker’s system log related knowledge.

1. What is Docker’s system log?

Docker's system log refers to the log information generated during the running process of the container, including standard output and standard error output. Standard output refers to the information output by the program through commands such as print() or cout during operation, while standard error output refers to the error message output by the program when it encounters an error. These log information are very important for Docker container monitoring and error troubleshooting, so Docker provides a variety of ways to collect, view, and manage container system logs. Let's take a look at the system log collection method provided by Docker.

2. Docker’s system log collection method

Docker provides a variety of ways to collect system log information of containers, including the following methods:

2.1 Use the docker logs command

The docker logs command can view the standard output and standard error output logs of the specified container. The syntax is as follows:

docker logs [OPTIONS] CONTAINER

Among them, OPTIONS is optional and you can specify the conditions for viewing the log. number, whether to follow log output, etc. CONTAINER specifies the container ID or container name of the log to be viewed. For example, to view the log information of the container with container ID abc123, you can use the following command:

docker logs -f abc123

This command will follow the log output of the container and display new log information.

2.2 Use the docker events command

The docker events command can view the event log of the Docker daemon, including the start and stop of the container. Different from the docker logs command, the docker events command can view the event information of all containers. The syntax is as follows:

docker events [OPTIONS]

Among them, OPTIONS is optional, and you can specify to view certain types of events, filter certain events, etc.

2.3 Use the docker inspect command

The docker inspect command can view the detailed information of the container, including the container's network settings, mount points and other information. The container's detailed information also includes the container's system log information. For example, to view the details of a container with container ID abc123, you can use the following command:

docker inspect abc123

3. Docker's system log configuration

In addition to using the log collection provided by Docker In addition to tools, we can also use third-party tools to collect and manage system logs of containers. For example, we can use the ELK tool to collect, store and analyze log information of Docker containers. Let's take a look at how to configure the container's log information collection method through Docker's log driver.

In Docker, you can use the following log drivers for log configuration:

• json-file: The default log driver outputs container logs to JSON files.
• syslog: Output container logs to syslog.
• journald: Output container logs to systemd-journald.
• gelf: Output container logs to Graylog Extended Log Format.
• fluentd: Output container logs to Fluentd.

In addition to these default log drivers, Docker also supports the use of third-party log drivers, such as logspout, logrotate, etc. We can use Docker's log driver to configure the container's log file location, format and other information. For example, you can use the following command to use the json-file driver to output container logs to the /var/log/docker directory:

docker run --log-driver=json-file --log-opt max-size=10m --log-opt max-file=3 -d nginx

In the above command, –log-driver=json-file is specified If the log driver is json-file, –log-opt max-size=10m and –log-opt max-file=3 specify the size and quantity limit of log files. In this way, when the container generates logs, the log information will be output to the /var/log/docker/container ID-json.log file.

4. Summary

In the Docker container life cycle, the system log is a very important link. It can help us monitor and maintain the status of the container to ensure that the container of normal operation. Docker provides a variety of ways to collect, view, and manage system log information of containers, including using commands such as docker logs, docker events, and docker inspect, and using third-party log drivers to configure log file location, format, and other information. We can choose appropriate log collection tools and configuration methods based on actual needs to better monitor and manage Docker containers.

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