DOCKER.md

Docker

In this third part of the tutorial, we are going to install Docker. The reason is very simple, we do not want to have to deal with the underlying Operating System, and go crazy when updates are needed. A couple of examples are Cabal and the GHC. Keeping them updated is important but messy. Having everything into containers greatly simplifies the management of the node.

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How to install Docker

There are a number of different ways of installing Docker. I found using snap, the new ubuntu packer manager, VERY simple.

All that you need to do is:

sudo snap install docker

Now that docker is installed, we need to give the ubuntu user, permissions to use it without requiring sudo privileges.

All that we need to do is to create a group and assign the ubuntu user to it.

sudo addgroup --system docker
sudo adduser ubuntu docker
newgrp docker

and then restart the docker service

sudo snap disable docker
sudo snap enable docker

On youtube I received the comment:

Hi. I see this Warning during the build " ---> [Warning] Your kernel does not support memory limit capabilities or the cgroup is not mounted. Limitation discarded. Is this going to be a problem for me?

So I quickly checked and yes there is an extra step to take in order to enable memory and cpu capabilities. Details below.

Enabling cgroup

Now that docker is installed, we have to add cgroup capabilities. These are required in order to make visible to containers cpu and memory resources.

It is really really simple to do so, first edit this file sudo vi /boot/firmware/cmdline.txt and add cgroup_enable=memory cgroup_memory=1 at the end of the uniq line of the file (not a new line as it won't work)

The result should be something like:

ubuntu@ubuntu:~$ cat /boot/firmware/cmdline.txt
net.ifnames=0 dwc_otg.lpm_enable=0 console=serial0,115200 console=tty1 root=LABEL=writable rootfstype=ext4 elevator=deadline rootwait fixrtc cgroup_enable=memory cgroup_memory=1

In order for these changes to take effect, you have to reboot your pi, so simply run sudo reboot now

And this is for this episode.