Installing and Configuring containerd as a Kubernetes Container Runtime

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In this post, I’m going to show you how to install containerd as the container runtime in a Kubernetes cluster. I will also cover setting the cgroup driver for containerd to systemd which is the preferred cgroup driver for Kubernetes. In Kubernetes version 1.20 Docker was deprecated and will be removed after 1.22. containerd is a CRI compatible container runtime and is one of the supported options you have as a container runtime in Kubernetes in this post Docker Kubernetes world. I do want to call out that you can use containers created with Docker in containerd.

Configure required modules

First load two modules in the current running environment and configure them to load on boot

sudo modprobe overlay
sudo modprobe br_netfilter

cat <<EOF | sudo tee /etc/modules-load.d/containerd.conf
overlay
br_netfilter
EOF

Configure required sysctl to persist across system reboots

cat <<EOF | sudo tee /etc/sysctl.d/99-kubernetes-cri.conf
net.bridge.bridge-nf-call-iptables  = 1
net.ipv4.ip_forward                 = 1
net.bridge.bridge-nf-call-ip6tables = 1
EOF

Apply sysctl parameters without reboot to current running enviroment

sudo sysctl --system

Install containerd packages

sudo apt-get update 
sudo apt-get install -y containerd

Create a containerd configuration file

sudo mkdir -p /etc/containerd
sudo containerd config default | sudo tee /etc/containerd/config.toml

Set the cgroup driver for runc to systemd

Set the cgroup driver for runc to systemd which is required for the kubelet.
For more information on this config file see the containerd configuration docs here and also here.

At the end of this section in /etc/containerd/config.toml

        [plugins."io.containerd.grpc.v1.cri".containerd.runtimes.runc]
        ...

Around line 86, add these two lines, indentation matters.

          [plugins."io.containerd.grpc.v1.cri".containerd.runtimes.runc.options]
            SystemdCgroup = true

Restart containerd with the new configuration

sudo systemctl restart containerd

And that’s it, from here you can install and configure Kubernetes on top of this container runtime. In an upcoming post, I will bootstrap a cluster using containerd as the container runtime.