[Release 1.26] Integrate tailscale into k3s

[manuelbuil]

Backport: #7353

[ShylajaDevadiga]

Validated tailscale integration into k3s using commit id 3668584 on release-1.26 branch

Environment Details

Infrastructure
Cloud EC2 instance

Node(s) CPU architecture, OS, and Version:
SLES15 SP3

Config.yaml on first node:

cat /etc/rancher/k3s/config,yaml
write-kubeconfig-mode: 644
token: <TOKEN>
cluster-init: true
vpn-auth: "name=tailscale,joinKey=tskey-auth-<AUTHKEY>"

Config.yaml on other nodes:

cat /etc/rancher/k3s/config,yaml
write-kubeconfig-mode: 644
token: <TOKEN>`
server: https://<tailscale IP on server 1>
vpn-auth: "name=tailscale,joinKey=tskey-auth-<AUTHKEY>"

Steps:

1. Create tailscale account
2. Generate auth key from the UI using Settings Tab -> Keys -> Generate auth. Enable Reusable, Set-expiration to 1-2 days or as long as you need the authKey for your nodes, and enable Ephemeral
3. Add the key generated to the config.
4. Install tailscale on every node that you would like to join the cluster and access over vpn including agent nodes
5. Install k3s using the configs above

Validation results

> ip a |grep tailscale
3: tailscale0: <POINTOPOINT,MULTICAST,NOARP,UP,LOWER_UP> mtu 1280 qdisc pfifo_fast state UNKNOWN group default qlen 500
    inet <REDACTED>/32 scope global tailscale0

> ip route show table 52
10.42.0.0/24 dev tailscale0 
10.42.1.0/24 dev tailscale0 
10.42.2.0/24 dev tailscale0 
10.42.3.0/24 dev tailscale0 
1.8.7.50 dev tailscale0 
1.8.1.51 dev tailscale0 
1.9.2.101 dev tailscale0 
1.1.1.100 dev tailscale0 
1.1.3.12 dev tailscale0

> kubectl get nodes -o wide
NAME               STATUS   ROLES                       AGE    VERSION                INTERNAL-IP      EXTERNAL-IP   OS-IMAGE                              KERNEL-VERSION         CONTAINER-RUNTIME
ip-<REDACTED>  Ready    <none>                      23m    v1.26.5+k3s-36685840   <REDACTED>     <none>        SUSE Linux Enterprise Server 15 SP3   5.3.18-59.37-default   containerd://1.7.1-k3s1
ip-<REDACTED>   Ready    control-plane,etcd,master   161m   v1.26.5+k3s-36685840   <REDACTED>      <none>        SUSE Linux Enterprise Server 15 SP3   5.3.18-59.37-default   containerd://1.7.1-k3s1
ip-<REDACTED>     Ready    control-plane,etcd,master   139m   v1.26.5+k3s-36685840   <REDACTED>   <none>        SUSE Linux Enterprise Server 15 SP3   5.3.18-59.37-default   containerd://1.7.1-k3s1
ip-<REDACTED>    Ready    control-plane,etcd,master   28m    v1.26.5+k3s-36685840   <REDACTED>   <none>        SUSE Linux Enterprise Server 15 SP3   5.3.18-59.37-default   containerd://1.7.1-k3s1

> kubectl get ep -A
NAMESPACE     NAME             ENDPOINTS                                                 AGE
default       kubernetes       <REDACTED>:6443,<REDACTED>:6443,<REDACTED>:6443   164m
kube-system   kube-dns                                                                   163m
kube-system   metrics-server                                                             163m