KTHW - The workers

July 26, 2020 - Reading time: 7 minutes
  • The worker nodes

The nodes are responsible for the actual work of running container applications managed by kubernetes. Components:

  • Kublet: agent running on the node. Provides the API to access the node.
  • Kube-proxy: manages iptable rules to provide virtual network access to pods.
  • container runtime: download images and run containers (ex. docker, containerd).

OS dependencies

  • Socat: Multipurpose relay (SOcket CAT) Socat is a command line based utility that establishes two bidirectional byte streams and transfers data between them. It enables support to the kubectl port-forward command.

  • Conntrack: command line interface for netfilter connection tracking Using conntrack , you can dump a list of all (or a filtered selection of) currently tracked connections, delete connections from the state table, and even add new ones.

  • Ipset: administration tool for IP sets A netfilter projectm some of the uses are: store multiple IP addresses or port numbers and match against the collection by iptables at one swoop; dynamically update iptables rules against IP addresses or ports without performance penalty; express complex IP address and ports based rulesets with one single iptables rule and benefit from the speed of IP sets

Worker binaries

  • cri-tools Introduced in Kubernetes 1.5, the Container Runtime Interface (CRI) is a plugin interface which enables kubelet to use a wide variety of container runtimes, without the need to recompile. https://github.com/kubernetes-sigs/cri-tools

  • runc runc is a CLI tool for spawning and running containers according to the OCI specification. Open Container Initiative is an open governance structure for the express purpose of creating open industry standards around container formats and runtimes. Currently contains two specifications: the Runtime Specification (runtime-spec) and the Image Specification (image-spec). The Runtime Specification outlines how to run a “filesystem bundle” that is unpacked on disk. https://github.com/opencontainers/runc

  • cni The Container Network Interface project, consists of a specification and libraries for writing plugins to configure network interfaces in Linux containers, along with a number of supported plugins. We'll use the cni-plugins project. This is a Cloud Native Computing Foundation (CNCF) project currently on incubation phase. (known incubation projects: etcd, cni) (known graduated projects from CNCF: kubernetes, prometheus, coreDNS, containerd, fluentd) https://github.com/containernetworking

  • containerd An industry-standard container runtime with an emphasis on simplicity, robustness and portability Graduated on Cloud Native Computing Foundation on 2019.

  • kubectl

  • kube-proxy

  • kublet

Install the binaries and OS dependencies

sudo -y install socat conntrack ipset
wget -q --show-progress --https-only --timestamping \
  https://github.com/kubernetes-sigs/cri-tools/releases/download/v1.18.0/crictl-v1.18.0-linux-amd64.tar.gz \
  https://github.com/opencontainers/runc/releases/download/v1.0.0-rc91/runc.amd64 \
  https://github.com/containernetworking/plugins/releases/download/v0.8.6/cni-plugins-linux-amd64-v0.8.6.tgz \
  https://github.com/containerd/containerd/releases/download/v1.3.6/containerd-1.3.6-linux-amd64.tar.gz \
  https://storage.googleapis.com/kubernetes-release/release/v1.18.6/bin/linux/amd64/kubectl \
  https://storage.googleapis.com/kubernetes-release/release/v1.18.6/bin/linux/amd64/kube-proxy \
  https://storage.googleapis.com/kubernetes-release/release/v1.18.6/bin/linux/amd64/kubelet
sudo mkdir -p \
  /etc/cni/net.d \
  /opt/cni/bin \
  /var/lib/kubelet \
  /var/lib/kube-proxy \
  /var/lib/kubernetes \
  /var/run/kubernetes
mkdir containerd
tar -xvf crictl-v1.18.0-linux-amd64.tar.gz
tar -xvf containerd-1.3.6-linux-amd64.tar.gz -C containerd
sudo tar -xvf cni-plugins-linux-amd64-v0.8.6.tgz -C /opt/cni/bin/
sudo mv runc.amd64 runc
chmod +x crictl kubectl kube-proxy kubelet runc 
sudo mv crictl kubectl kube-proxy kubelet runc /usr/local/bin/
sudo mv containerd/bin/* /bin/ 

Configure containerd

sudo mkdir -p /etc/containerd/
cat << EOF | sudo tee /etc/containerd/config.toml
[plugins]
  [plugins.cri.containerd]
    snapshotter = "overlayfs"
    [plugins.cri.containerd.default_runtime]
      runtime_type = "io.containerd.runtime.v1.linux"
      runtime_engine = "/usr/local/bin/runc"
      runtime_root = ""
EOF
cat <<EOF | sudo tee /etc/systemd/system/containerd.service
[Unit]
Description=containerd container runtime
Documentation=https://containerd.io
After=network.target

[Service]
ExecStartPre=/sbin/modprobe overlay
ExecStart=/bin/containerd
Restart=always
RestartSec=5
Delegate=yes
KillMode=process
OOMScoreAdjust=-999
LimitNOFILE=1048576
LimitNPROC=infinity
LimitCORE=infinity

[Install]
WantedBy=multi-user.target
EOF

Configure the kubelet

HOSTNAME=$(hostname)
sudo mv ${HOSTNAME}-key.pem ${HOSTNAME}.pem /var/lib/kubelet/
sudo mv ${HOSTNAME}.kubeconfig /var/lib/kubelet/kubeconfig
sudo mv ca.pem /var/lib/kubernetes/
cat << EOF | sudo tee /var/lib/kubelet/kubelet-config.yaml
kind: KubeletConfiguration
apiVersion: kubelet.config.k8s.io/v1beta1
authentication:
  anonymous:
    enabled: false
  webhook:
    enabled: true
  x509:
    clientCAFile: "/var/lib/kubernetes/ca.pem"
authorization:
  mode: Webhook
clusterDomain: "cluster.local"
clusterDNS: 
  - "10.32.0.10"
runtimeRequestTimeout: "15m"
tlsCertFile: "/var/lib/kubelet/${HOSTNAME}.pem"
tlsPrivateKeyFile: "/var/lib/kubelet/${HOSTNAME}-key.pem"
EOF
cat << EOF | sudo tee /etc/systemd/system/kubelet.service
[Unit]
Description=Kubernetes Kubelet
Documentation=https://github.com/kubernetes/kubernetes
After=containerd.service
Requires=containerd.service

[Service]
ExecStart=/usr/local/bin/kubelet \\
  --config=/var/lib/kubelet/kubelet-config.yaml \\
  --container-runtime=remote \\
  --container-runtime-endpoint=unix:///var/run/containerd/containerd.sock \\
  --image-pull-progress-deadline=2m \\
  --kubeconfig=/var/lib/kubelet/kubeconfig \\
  --network-plugin=cni \\
  --register-node=true \\
  --v=2 \\
  --hostname-override=${HOSTNAME} \\
Restart=on-failure
RestartSec=5

[Install]
WantedBy=multi-user.target
EOF

configure the kubernetes proxy

sudo mv kube-proxy.kubeconfig /var/lib/kube-proxy/kubeconfig
cat << EOF | sudo tee /var/lib/kube-proxy/kube-proxy-config.yaml
kind: KubeProxyConfiguration
apiVersion: kubeproxy.config.k8s.io/v1alpha1
clientConnection:
  kubeconfig: "/var/lib/kube-proxy/kubeconfig"
mode: "iptables"
clusterCIDR: "10.200.0.0/16"
EOF
cat << EOF | sudo tee /etc/systemd/system/kube-proxy.service
[Unit]
Description=Kubernetes Kube Proxy
Documentation=https://github.com/kubernetes/kubernetes

[Service]
ExecStart=/usr/local/bin/kube-proxy \\
  --config=/var/lib/kube-proxy/kube-proxy-config.yaml
Restart=on-failure
RestartSec=5

[Install]
WantedBy=multi-user.target
EOF

Verify that the workers have registered with the controllers

We can check this from one of the controllers:

cloud_user@ctl01:~$ kubectl get nodes --kubeconfig admin.kubeconfig
NAME             STATUS     ROLES    AGE     VERSION
wrk01.kube.com   NotReady   <none>   10m     v1.18.6
wrk02.kube.com   NotReady   <none>   3m38s   v1.18.6