Docker Logs & Monitoring

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

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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.s…"   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

👉 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": {}
},

👉 We can see that log files are saved in JSON format in the host system

💡 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"
 }
}

💡 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"
 }
},

👉 We can confirm that the container started with the log rotate configurations

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Utilizing Docker Events

With another terminal connected, we will enter

docker events

👉 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 <[e-mail]>, name=events_con)
.
.
.
2023-03-06T14:35:15.131094800+09:00 container destroy 6ec4910cc606a135ca6fe1d10b8f9fdaf88c5dc008e53c00f28c7d1e8325f51b (image=nginx:latest, maintainer=NGINX Docker Maintainers <[e-mail]>, name=events_con)

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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.

👉 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

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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 ✔