Introduction
Effective log and monitoring management is essential for ensuring the health and performance of Docker containers. By leveraging Docker's built-in log and monitoring tools, as well as third-party tools, we can gain insights into our containers' behavior and troubleshoot any issues that arise
I will be utilizing docker logs
and docker events
commands to manage logs. Furthermore, I will also use cAdvisor to monitor logs
Utilizing Docker Logs
Starting a mysql container
docker run -d --name log_con1 mysql:5.7
Checking the status
docker ps -a
8f2640092ab8 mysql:5.7 "docker-entrypoint.sโฆ" 17 minutes ago Exited (1) 10 seconds ago log_con1
To check logs for this container
docker logs log_con1
.
.
2023-03-06 05:04:29+00:00 [ERROR] [Entrypoint]: Database is uninitialized and password option is not specified
You need to specify one of the following as an environment variable:
- MYSQL_ROOT_PASSWORD
- MYSQL_ALLOW_EMPTY_PASSWORD
- MYSQL_RANDOM_ROOT_PASSWORD
Now, to test live logs, we will start another container
docker run -it --name log_con2 ubuntu:bionic
Opening another terminal and entering the following
docker logs -f log_con2
๐ It will be in a standby to wait for any action in the ubuntu container
From the container
echo "Log Test"
We will be able to see the logs from the host system on the other terminal
root@6246287978ac:/# echo "Log Test"
Log Test
We can inspect the container to confirm how logs are saved
docker container inspect log_con2
"LogConfig": {
"Type": "json-file",
"Config": {}
},
๐ We can see that log files are saved in JSON format in the host system
๐ก The log files are present under
/var/lib/docker/containers/
We can also edit the docker daemon file to rotate logs if they reach a certain size or value
vi /etc/docker/daemon.json
{
"log-driver": "json-file",
"log-opts": {
"max-size": "10k",
"max-file": "5"
}
}
๐ก If there is no
daemon.json
file, we can create one
Restarting the daemon and docker service
systemctl daemon-reload
systemctl restart docker
Starting another container
docker run -d --name log_con3 ubuntu:bionic
docker container inspect log_con3
"LogConfig": {
"Type": "json-file",
"Config": {
"max-file": "5",
"max-size": "10k"
}
},
๐ We can confirm that the container started with the log rotate configurations
Utilizing Docker Events
With another terminal connected, we will enter
docker events
๐ On standby mode to fetch live logs
From the other terminal,
docker run -d --name events_con nginx:latest
docker rm -f events_con
Now going back to the first terminal to check logs,
docker events
2023-03-06T14:35:09.394975329+09:00 container create 6ec4910cc606a135ca6fe1d10b8f9fdaf88c5dc008e53c00f28c7d1e8325f51b (image=nginx:latest, maintainer=NGINX Docker Maintainers <docker-maint@nginx.com>, name=events_con)
.
.
.
2023-03-06T14:35:15.131094800+09:00 container destroy 6ec4910cc606a135ca6fe1d10b8f9fdaf88c5dc008e53c00f28c7d1e8325f51b (image=nginx:latest, maintainer=NGINX Docker Maintainers <docker-maint@nginx.com>, name=events_con)
Utilizing Container Advisor
cAdvisor (Container Advisor) is an open-source container monitoring tool that is integrated with Docker. It is designed to provide detailed information about the resource usage and performance of running containers, including CPU, memory, disk, and network utilization.
๐ The best part about this tool is that we can examine container logs via a WEB interface
Starting a cAdvisor container
docker run \
--volume=/:/rootfs:ro \
--volume=/var/run:/var/run:rw \
--volume=/sys/fs/cgroup:/sys/fs/cgroup:ro \
--volume=/dev/disk/:/dev/disk:ro \
--privileged=true \
--publish=8080:8080 \
--detach=true \
--name=cAdvisor google/cadvisor:latest
Now if we open our browser and go to the address of our host linux system
I wil use a Stress container to check CPU usage via cAdvisor
docker run --rm -d progrium/stress --cpu 2 --vm 2 --vm-bytes 128M --timeout 30s
Conclusion
In conclusion, managing Docker logs is essential for monitoring the health and performance of Docker containers. I utilized several docker commands and an open-source tool to keep tabs with our container logs โ
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