When starting K3s server with –cluster-init it will run all control plane components that includes (api server, controller manager, scheduler, and etcd). However you can run server nodes with certain components and execlude others, the following sectiohs will explain how to do that.

ETCD Only Nodes

This document assumes you run K3s server with embedded etcd by passing --cluster-init flag to the server process.

To run a K3s server with only etcd components you can pass --disable-api-server --disable-controller-manager --disable-scheduler flags to k3s, this will result in running a server node with only etcd, for example to run K3s server with those flags:

curl -fL https://get.k3s.io | sh -s - server --cluster-init --disable-api-server --disable-controller-manager --disable-scheduler

You can join other nodes to the cluster normally after that.

Disable ETCD

You can also disable etcd from a server node and this will result in a k3s server running control components other than etcd, that can be accomplished by running k3s server with flag --disable-etcd for example to join another node with only control components to the etcd node created in the previous section:

curl -fL https://get.k3s.io | sh -s - server --token <token> --disable-etcd --server https://<etcd-only-node>:6443 

The end result will be a two nodes one of them is etcd only node and the other one is controlplane only node, if you check the node list you should see something like the following:

kubectl get nodes
NAME              STATUS   ROLES                       AGE     VERSION
ip-172-31-13-32   Ready    etcd                        5h39m   v1.20.4+k3s1
ip-172-31-14-69   Ready    control-plane,master        5h39m   v1.20.4+k3s1

Note that you can run kubectl commands only on the k3s server that has the api running, and you cant run kubectl commands on etcd only nodes.

Re-enabling control components

In both cases you can re-enable any component that you already disabled simply by removing the corresponding flag that disables them, so for example if you want to revert the etcd only node back to a full k3s server with all components you can just remove the following 3 flags --disable-api-server --disable-controller-manager --disable-scheduler, so in our example to revert back node ip-172-31-13-32 to a full k3s server you can just re-run the curl command without the disable flags:

curl -fL https://get.k3s.io | sh -s - server --cluster-init

you will notice that all components started again and you can run kubectl commands again:

kubectl get nodes
NAME              STATUS   ROLES                       AGE     VERSION
ip-172-31-13-32   Ready    control-plane,etcd,master   5h45m   v1.20.4+k3s1
ip-172-31-14-69   Ready    control-plane,master        5h45m   v1.20.4+k3s1

Notice that role labels has been re-added to the node ip-172-31-13-32 with the correct labels (control-plane,etcd,master).

Add disable flags using the config file

In any of the previous situation you can use the config file instead of running the curl commands with the associated flags, for example to run an etcd only node you can add the following options to the /etc/rancher/k3s/config.yaml file:

disable-api-server: true
disable-controller-manager: true
disable-scheduler: true
cluster-init: true

and then start K3s using the curl command without any arguents:

curl -fL https://get.k3s.io | sh -