While looking for ways to monitor containers with open source solutions, I read a very interesting paper from Rancher labs: Comparing Seven Monitoring Options for Docker.
I started to play with Prometheus but it will take me some more time to be really useable. Recently I also found an interesting Docker UI while reading a paper on ARM clustering. This topic alone could justify a dedicated post but for the moment I will stick with Cadvisor and docker-ui.
These two complementary solutions are not good enough for monitoring a docker swarm but again Prometheus looks promising, but will require more work on my side before having something to publish.
Now the question I asked myself is how to ensure that the monitoring containers are launched on startup. Easy enough the instructions in the Docker administration guide are pretty straight forward.
Because I run Hypriot OS on my nodes, which is basically a stripped down Raspbian with docker pre-installed and a cool list of fancy features like Avahi, the out-of-the-box process manager is systemd.
In my case I obviously also used one of the ARM version of the official CAdvisor docker.
The first step is to define the service file in /etc/systemd/system.
Enter the following command:
sudo nano /etc/systemd/system/docker-ca_advisor.service
And copy/paste the below content:
[Unit]
Description=CA Advisor container
Requires=docker.service
After=docker.service
[Service]
Restart=always
ExecStart=/usr/bin/docker run --volume=/:/rootfs:ro --volume=/var/run:/var/run:rw --volume=/sys:/sys:ro --volume=/var/lib/docker/:/var/lib/docker:ro --publish=8080:8080 --name=cadvisor robinthrift/raspbian-cadvisor
ExecStop=/usr/bin/docker stop -t 2 cadvisor
ExecStopPost=/usr/bin/docker rm -f cadvisor
[Install]
WantedBy=default.target
Note: when trying to implement my own instructions for docker-ui I encountered an issue. The container was stopping and restarting within seconds. It took me sometime to realise that you cannot just copy/paste the command line you use to launch manually the container. Indeed the option -d must not be specified in a service file. So the ExecStart for Dockerui is
docker run -p 9000:9000 -v /var/run/docker.sock:/var/run/docker.sock --name=dockerui hypriot/rpi-dockerui
To start using the service, reload systemd and start the service:
sudo systemctl daemon-reload
sudo systemctl start docker-ca_advisor.service
To enable the service at system startup, execute:
sudo systemctl enable docker-ca_advisor.service
To access the Cadvisor page, point your favorite browser to http://IPADRESS:8080 where you replace IPADDRESS by the IP address of the docker node you want to monitor.
And the Docker-ui dashboard on the port 9000
