30/10/2021
Ok, so, this is gonna be short and simple...for the most part .😅
We will be setting up Docker Engine on Ubuntu 20.04 as a systemd service.
First, Older versions of Docker were called docker, docker.io, or docker-engine
If you have any of those installed, first remove them.
sudo apt-get remove docker docker-engine docker.io containerd runc
The contents of /var/lib/docker/, including images, containers, volumes, and
networks, will be preserved from your previous installation.
If you want a clean start, do this
sudo rm -rf /var/lib/docker
sudo rm -rf /var/lib/containerd
WARNING, this will remove your docker volumes, images, and dataSetup Repository
1. Update apt and required packages
sudo apt-get update
sudo apt-get install \
ca-certificates \
curl \
gnupg \
lsb-release
2. Add Docker's official GPG key
curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo gpg --dearmor -o /usr/share/keyrings/docker-archive-keyring.gpg
3. Setup Docker's stable repository
echo \
"deb [arch=$(dpkg --print-architecture) signed-by=/usr/share/keyrings/docker-archive-keyring.gpg] https://download.docker.com/linux/ubuntu \
$(lsb_release -cs) stable" | sudo tee /etc/apt/sources.list.d/docker.list > /dev/null
Install Docker Engine
sudo apt-get update
sudo apt-get install docker-ce docker-ce-cli containerd.io
Since we installed via the apt package manager, updating is as simple as
sudo apt-get update
Now, Docker is installed and set up as a systemd service named docker.service,
and its service file is stored in /lib/systemd/system/docker.service
You can check its status with
sudo systemctl status docker
You can verify by running a test container,
docker run hello-world
This will print a test message then exit.
You can also start, stop, restart, disable or enable docker daemon by running
sudo systemctl start docker
sudo systemctl stop docker
sudo systemctl restart docker
sudo systemctl disable docker
sudo systemctl enable docker
To list running container
docker container ls
To list all containers (start and stopped)
docker container ls -a
To create or create and run a container
docker create --name containername imageurl
docker run --name containername imageurl
Refer to here for more detailed instructions
https://docs.docker.com/engine/reference/commandline/create/
To pull a new docker image
docker pull imageurl
To start, stop, or restart a container
docker start containername
docker stop containername
docker restart containername
To update a container
docker stop containername
docker rm containername
docker pull imageurl
docker run --name containername imageurl
Remember to use the same run/create command you used previously to run/create
the container. It's handy to keep all your docker run commands in a text file
somewhere.
Docker daemon also has a neat feature of restarting docker daemon without
stopping any of your containers, in case you want to update docker daemon or
something.
Edit your /etc/docker/daemon.json file
sudo nano /etc/docker/daemon.json
and add this
{
"live-restore": true
}
then press ctrl+x then Y and Enter to save.
Restart Policies
Docker has something called restart policies to manage the automatic start and
stop of your container. Following restart policies are available,
1. no : Do not automatically restart the container. (the default)
2. on-failure : Restart the container if it exits due to an error, which
manifests as a non-zero exit code.
3. always : Always restart the container if it stops. If it is manually
stopped, it is restarted only when Docker daemon restarts or the container
itself is manually restarted. (See the second bullet listed in restart
policy details)
4. unless-stopped : Similar to always, except that when the container is
stopped (manually or otherwise), it is not restarted even after Docker
daemon restarts.
You can set any of them via the --restart flag while creating a container.
Managing Docker Containers via Systemd
Although it is recommended to use restart policies to manage containers, I'm
gonna show you how to manage them via systemd service of your host ubuntu.
Suppose you want to start or stop containers based on some system events, like
after you have successfully run a system check on boot, or after you have your
external storage device plugged in and ready to be mounted inside your
containers.
Remember, if you want to manage docker containers via systemd, put --restart no
flag in your container.
Simply, create a containername.service file in /etc/systemd/system directory,
and add the following
[Unit]
Description=Docker Conatiner name
After=network-online.target docker.service
Requires=docker.service
StartLimitIntervalSec=10
StartLimitBurst=5
[Service]
Type=simple
ExecStart=/usr/bin/docker start -a containername
ExecStop=/usr/bin/docker stop containername
Restart=always
RestartSec=10s
[Install]
WantedBy=docker.service
Then reload systemctl, start and enable your service
sudo systemctl daemon-reload
sudo systemctl start containername
sudo systemctl enable coontainername
This will start your container after you have network connectivity and your
docker daemon is ready. Also, in case your container stops due to some reason,
it will automatically restart them, and keep restarting (you can remove
Restart=always to disable that) at a 10 seconds interval (you can adjust it with
RestartSec=10s value) whenever it stops.
The After= specifies the service after which this service will run.
The Requires= specifies the dependant service, without which this service won't
start. (it's more or less the same as after but both are required in this case)
The WantedBy= puts your service in the specifiedservice.service.wants folder. So
basically, whenever the specified service runs, this service will be started
too.
If you want your container service to start only and only after your foo.service
has started, you would put only foo.service in all three after, requires, and
wantedby.
To view container status via systemd
sudo systemctl status containername
To view full logs via systemd
sudo journalctl -f -u containername
or via docker daemon
docker logs containername
Refer to systemd man page for more info.
https://www.freedesktop.org/software/systemd/man/systemd.unit.html
Uninstall Docker Engine
Like most things in life, removing is as simple as
1. Remove packages
sudo apt-get purge docker-ce docker-ce-cli containerd.io
2. Remove images, containers & volumes
sudo rm -rf /var/lib/docker
sudo rm -rf /var/lib/containerd
WARNING, this will remove your docker volumes, images, and dataWasn't that quick
🤣
Installing docker engine on ubuntu 20.04 and managing containers via systemd
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