Adding a worker node only with MicroK8s

balchua1 · February 12, 2021, 8:08am

This document describes the steps on how to join a worker node only into your Highly Available MicroK8s.

This has the main advantage that, you can avoid the resource overhead of the control plane. The overhead can go up to GBs and several CPU cycles. These cycles are best allocated to your workload instead of Kubernetes.

Before you begin, you need to have the following in place:

An HA cluster, example 3 node HA MicroK8s cluster
Load balancer to front the apiserver.

Setup a 3 node HA MicroK8s

Follow the instructions in MicroK8s documentation.

Load balancer

Follow the steps below, if you want to use a cloud provider load balancer

On each of your HA MicroK8s node, add the load balancer IP into the file /var/snap/microk8s/current/certs/cs.conf.template

For example:

[ req ]
default_bits = 2048
prompt = no
default_md = sha256
req_extensions = req_ext
distinguished_name = dn

[ dn ]
C = GB
ST = Canonical
L = Canonical
O = Canonical
OU = Canonical
CN = 127.0.0.1

[ req_ext ]
subjectAltName = @alt_names

[ alt_names ]
DNS.1 = kubernetes
DNS.2 = kubernetes.default
DNS.3 = kubernetes.default.svc
DNS.4 = kubernetes.default.svc.cluster
DNS.5 = kubernetes.default.svc.cluster.local
IP.1 = 127.0.0.1
IP.2 = 10.152.183.1
IP.99 = 167.172.5.46
#MOREIPS

[ v3_ext ]
authorityKeyIdentifier=keyid,issuer:always
basicConstraints=CA:FALSE
keyUsage=keyEncipherment,dataEncipherment,digitalSignature
extendedKeyUsage=serverAuth,clientAuth
subjectAltName=@alt_names

Note that IP.99 = 167.172.5.46 is the Load balancer IP

Simple Load Balancer per node

The steps below uses a load balancer installed on each node.

In this step, we will use Traefik to load balance between the Kubernetes ApiServer.

Download Traefik binary, and place it in to /usr/local/bin directory.

Configure traefik.yaml

You need to create the traefik.yaml configuration file in /etc/traefik/traefik.yaml, for example:

## Static configuration
entryPoints:
  apiserver:
    address: ":16443"
providers:
  file:
    filename: /etc/traefik/providers.yaml
    watch: true

Then configure the provider into the location /etc/traefik/provider.yaml (as shown above).

tcp:
routers:
  Router-1:
    # Listen to any SNI
    rule: "HostSNI(`*`)"
    service: "kube-apiserver"
    tls:
      passthrough: true
services:
  kube-apiserver:
    loadBalancer:
      servers:
      - address: "10.130.0.2:16443"
      - address: "10.130.0.3:16443"
      - address: "10.130.0.4:16443"

Each of the address represents the IP address and port of the apiservers.

Start traefik, or setup a systemd service for traefik

Install MicroK8s

On your worker node, install MicroK8s like usual.

For versions 1.20

snap install microk8s --classic --channel 1.20/stable

Stopping the services

You need to stop all the services on this worker node.

For versions 1.19 or 1.20

systemctl stop snap.microk8s.daemon-apiserver
systemctl stop snap.microk8s.daemon-apiserver-kicker.service 
systemctl stop snap.microk8s.daemon-controller-manager.service 
systemctl stop snap.microk8s.daemon-control-plane-kicker.service 
systemctl stop snap.microk8s.daemon-scheduler.service 
systemctl stop snap.microk8s.daemon-kubelet.service 
systemctl stop snap.microk8s.daemon-proxy.service

For kubelite version

Stop the kubelite service

systemctl stop snap.microk8s.daemon-kubelite.service

Token generation and known_tokens

On each worker node run the following:

Example:

# openssl rand -base64 32 | base64
KzVIdjBkUWFNYStQc01xb09lMXM1VEFRUVAxSHIxQ3I5UHk5bjZiSVdidz0K

Keep the generated random string.

On each of your control plane nodes, edit the file /var/snap/microk8s/current/credentials/known_tokens.csv and add the following.

KzVIdjBkUWFNYStQc01xb09lMXM1VEFRUVAxSHIxQ3I5UHk5bjZiSVdidz0K,system:kube-proxy,kube-proxy
KzVIdjBkUWFNYStQc01xb09lMXM1VEFRUVAxSHIxQ3I5UHk5bjZiSVdidz0K,system:node:worker-1,kubelet-1,"system:nodes"

Restart each control plane api server.

systemctl restart snap.microk8s.daemon-apiserver

Copy certificates to the worker node

scp root@controlplanenode:/var/snap/microk8s/current/certs/ca.crt /tmp/ca.crt
scp root@controlplanenode:/var/snap/microk8s/current/credentials/kubelet.config /tmp/kubelet.config
scp root@controlplanenode:/var/snap/microk8s/current/credentials/proxy.config /tmp/proxy.config

#copy the files to the worker nodes
scp /tmp/ca.crt root@workernode:/var/snap/microk8s/current/certs/ca.crt
scp /tmp/kubelet.config root@workernode:/var/snap/microk8s/current/credentials/kubelet.config
scp /tmp/proxy.config root@workernode:/var/snap/microk8s/current/credentials/proxy.config

Modify the config tokens

Before starting the kubelet and proxy, you need to modify the token located in /var/snap/microk8s/current/credentials/kubelet.config and /var/snap/microk8s/current/credentials/proxy.config.

If you are using the node based simple load balancer, simple use server: https://127.0.0.1:16443 in the /var/snap/microk8s/current/credentials/kubelet.config and /var/snap/microk8s/current/credentials/proxy.config

As an example:

apiVersion: v1
clusters:
- cluster:
    certificate-authority-data: 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
    server: https://your-load-balancer-ip or https://127.0.0.1:16443 if using simple node based LB
  name: microk8s-cluster
contexts:
- context:
    cluster: microk8s-cluster
    user: kubelet
  name: microk8s
current-context: microk8s
kind: Config
preferences: {}
users:
- name: kubelet
  user:
    token: KzVIdjBkUWFNYStQc01xb09lMXM1VEFRUVAxSHIxQ3I5UHk5bjZiSVdidz0K

Additional Kubelet configuration

When enabling the DNS, you need to start the worker node’s kubelet with these additional arguments/parameters.

From the file /var/snap/microk8s/current/args/kubelet add at the bottom of the file the following.

--cluster-domain=cluster.local
--cluster-dns=10.152.183.10

Start the Kubelet and Kube-proxy

Prevent the control plane from starting

The procedure below will prevent the control plane from starting when the MicroK8s snap is refreshed.

Create a file /var/snap/microk8s/current/var/lock/clustered.lock on each worker node.

Starting the service on 1.19 or 1.20

In each of the worker node

systemctl start snap.microk8s.daemon-kubelet.service
systemctl start snap.microk8s.daemon-proxy.service

Starting the service on kubelite version

systemctl stop snap.microk8s.daemon-kubelite.service

Check the cluster

From one of the master node.

Cordon off the control plane nodes.

microk8s kubectl cordon mk8s-cp-01 mk8s-cp-02 mk8s-cp-03

# microk8s kubectl get no -o wide
NAME         STATUS                     ROLES    AGE     VERSION                     INTERNAL-IP   EXTERNAL-IP   OS-IMAGE             KERNEL-VERSION     CONTAINER-RUNTIME
mk8s-cp-02   Ready,SchedulingDisabled   <none>   6d23h   v1.20.2-36+a377b7383d340b   10.130.0.3    <none>        Ubuntu 20.04.1 LTS   5.4.0-51-generic   containerd://1.3.7
mk8s-wk-01   Ready                      <none>   6d23h   v1.20.2-36+a377b7383d340b   10.130.0.5    <none>        Ubuntu 20.04.1 LTS   5.4.0-51-generic   containerd://1.3.7
mk8s-cp-01   Ready,SchedulingDisabled   <none>   6d23h   v1.20.2-36+a377b7383d340b   10.130.0.2    <none>        Ubuntu 20.04.1 LTS   5.4.0-51-generic   containerd://1.3.7
mk8s-cp-03   Ready,SchedulingDisabled   <none>   6d23h   v1.20.2-36+a377b7383d340b   10.130.0.4    <none>        Ubuntu 20.04.1 LTS   5.4.0-51-generic   containerd://1.3.7

Below shows the utilization of kubelet and kube-proxy. Running on a 1 CPU and 2 GB VM. As you can see, the node is very much dedicated to your workloads and not kubernetes.

Compare that to a control plane node resource usage.

Now you can run MicroK8s on a resource constrained environment. Profit!!!

metabsd · February 12, 2021, 1:26pm

Wich port you have to open on the load balancer side ?
Only 16443 ?

metabsd · February 12, 2021, 1:29pm

You mean /var/snap/microk8s/current/certs/csr.conf.template

balchua1 · February 12, 2021, 2:16pm

Oh yes. Thanks for correcting.

balchua1 · February 12, 2021, 2:17pm

I opened port 443 at the LB side. I was using a DigitalOcean cloud provider’s LB.

metabsd · February 12, 2021, 2:38pm

I talking about this one. When you mention to use a load balancer for the api-server. I understand that you use a load balancer for the port 16443 that microk8s used to communicate on the api-server lever.

balchua1 · February 12, 2021, 8:58pm

Yes. LB for the port 16443 of the apiserver.

balchua1 · February 20, 2021, 2:40am

I’ve added some instructions on how to use Traefik to Load Balance requests from kubelet and kube-proxy to the apiservers. Traefik can be installed on each node.

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