We recently acquired a new Hetzner bare-metal server to expand our Kubernetes cluster capacity. This guide walks through the complete process of provisioning the server, configuring networking with Hetzner’s vSwitch, setting up firewall rules, and joining it to our existing K3s cluster as an agent node.

Our infrastructure consists of bare-metal servers running K3s on Rocky Linux 10, connected through Hetzner’s vSwitch for secure private networking. The new node, which we’ll call ci-mystique, will join our existing cluster with master node ci-kang (10.0.0.1) and agent node ci-juggernaut (10.0.0.2).

Overview

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Installing the OS

First, we need to provision the server with our operating system. In the Hetzner Robot web interface, we configure the server name following our naming convention (e.g., ci-mystique) and set up a reverse DNS entry for it (e.g., mystique.ci.example.com). This makes it easier to identify the server later and is useful for monitoring and logging purposes.

After ordering the server, Hetzner sends an email with the root login credentials. We use these to access the server for the first time:

$ ssh [email protected]
Password: *** # From Email

We’ll use Hetzner’s installimage tool to install Rocky Linux 10, which we’ve chosen to maintain consistency with our existing nodes. The installation process is straightforward - run the command and configure your preferences in the text editor that opens:

root@server:~# installimage

In the configuration editor, set the hostname to match your naming convention (e.g., ci-mystique). We use the default partitioning scheme, which allocates 32GB for swap, 1GB for the boot partition, and the remainder for the root filesystem:

PART  swap   swap   32G
PART  /boot  ext3   1024M
PART  /      ext4   all

After the installation completes, reboot the server to boot into the new operating system:

$ reboot

When you try to reconnect via SSH, you’ll likely encounter a host identification warning. This is expected because the server’s SSH host keys have changed with the new OS installation:

203.0.113.10 ssh [email protected]
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@ WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED! @
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!
Someone could be eavesdropping on you right now (man-in-the-middle attack)!
It is also possible that a host key has just been changed.
The fingerprint for the ED25519 key sent by the remote host is
SHA256:EC/+6o18GyFj7/hRLmijBGbRLCaxsdMkryOtsGDCi7c.
Please contact your system administrator.
Add correct host key in /Users/Philip/.ssh/known_hosts to get rid of this message.
Offending RSA key in /Users/Philip/.ssh/known_hosts:71
Host key for 203.0.113.10 has changed and you have requested strict checking.
Host key verification failed.

To resolve this, remove the old SSH host key entries from your ~/.ssh/known_hosts file. Open the file in your text editor and delete the lines corresponding to the server’s IP address. On the next connection attempt, SSH will prompt you to verify and save the new host key:

$ ssh [email protected]
The authenticity of host '203.0.113.10 (203.0.113.10)' can't be established.
ED25519 key fingerprint is SHA256:EC/+6o18GyFj7/hRLmijBGbRLCaxsdMkryOtsGDCi7c.
This key is not known by any other names.
Are you sure you want to continue connecting (yes/no/[fingerprint])? yes
Warning: Permanently added '203.0.113.10' (ED25519) to the list of known hosts.
[email protected]'s password: ***

Setting up the OS

With the operating system installed, we need to perform some essential security and configuration steps. First and most important, change the default root password to something secure:

$ passwd
New password: ***
Retype new password: ***
passwd: password updated successfully

Next, update all packages to ensure the system has the latest security patches:

$ yum update -y

Now we’ll create a dedicated user account for daily operations. It’s best practice to avoid using the root account directly. Create a new user (e.g. philprime in my case), set their password, and add them to the wheel group to grant sudo privileges:

$ useradd philprime
$ passwd philprime
$ usermod -aG wheel philprime

Test that the new user account works by opening a new SSH session:

$ ssh [email protected]
[email protected]'s password: ***
Last login: Sat Nov 23 10:15:42 2025 from 98
[philprime@ci-mystique ~]$

Setting up SSH key authentication

With password authentication working, we can now set up SSH key-based authentication for more secure and convenient access. Generate an ED25519 key pair on your local machine and copy the public key to the server:

$ ssh-keygen -t ed25519 -f ~/.ssh/ci-mystique_philprime_ed25519
$ ssh-copy-id -i ~/.ssh/ci-mystique_philprime_ed25519 [email protected]
$ ssh-add --apple-use-keychain ~/.ssh/ci-mystique_philprime_ed25519

Add an entry to your ~/.ssh/config file for easy access (adjust the IP address as needed):

Host 203.0.113.10
  AddKeysToAgent yes
  UseKeychain yes
  IdentityFile ~/.ssh/ci-mystique_philprime_ed25519
  IdentitiesOnly yes
  User philprime

Verify that key-based authentication works:

$ ssh 203.0.113.10
Last login: Sat Nov 23 10:20:15 2025 from 98
[philprime@ci-mystique ~]$

From this point forward, we’ll use the non-root user account for all operations, using sudo when elevated privileges are required. As a final security measure, disable root login via SSH to protect against automated attacks:

$ sudo vi /etc/ssh/sshd_config
PermitRootLogin no

$ sudo systemctl restart sshd

Optional: Setting up Tailscale

We use Tailscale to create a secure mesh network for easier access to our cluster nodes. This is optional but highly recommended for remote management. Follow these steps to install and configure Tailscale on Rocky Linux:

Add the Tailscale repository and install the package:

$ sudo dnf config-manager --add-repo https://pkgs.tailscale.com/stable/centos/10/tailscale.repo
Adding repo from: https://pkgs.tailscale.com/stable/centos/10/tailscale.repo

$ sudo dnf install tailscale
Tailscale stable
Importing GPG key 0x957F5868:
  Userid     : "Tailscale Inc. (Package repository signing key) <[email protected]>"
  Fingerprint: 2596 A99E AAB3 3821 893C 0A79 458C A832 957F 5868
  From       : https://pkgs.tailscale.com/stable/centos/10/repo.gpg
Is this ok [y/N]: y
...
Installed:
tailscale-1.90.8-1.x86_64

Complete!

Enable and start the Tailscale service:

$ sudo systemctl enable --now tailscaled
Created symlink '/etc/systemd/system/multi-user.target.wants/tailscaled.service' → '/usr/lib/systemd/system/tailscaled.service'.

Connect the machine to your Tailscale network. This command will provide a URL for browser authentication:

$ sudo tailscale up

To authenticate, visit:

  https://login.tailscale.com/a/123456789abc

After authentication, verify the Tailscale IP address:

$ tailscale ip -4
100.64.1.10
NOTE: For servers and remotely accessed devices, consider disabling key expiry in the Tailscale admin console to avoid periodic re-authentication.

Update your ~/.ssh/config file to include the Tailscale hostname:

Host 203.0.113.10 ci-mystique.my-tail-net.ts.net
  AddKeysToAgent yes
  UseKeychain yes
  IdentityFile ~/.ssh/ci-mystique_philprime_ed25519
  IdentitiesOnly yes
  User philprime

Test the connection using the Tailscale hostname:

$ ssh ci-mystique.my-tail-net.ts.net
The authenticity of host 'ci-mystique.my-tail-net.ts.net (100.64.1.10)' can't be established.
ED25519 key fingerprint is SHA256:EC/+6o18GyFj7/hRLmijBGbRLCaxsdMkryOtsGDCi7c.
This host key is known by the following other names/addresses:
    ~/.ssh/known_hosts:69: 203.0.113.10
Are you sure you want to continue connecting (yes/no/[fingerprint])? yes
Warning: Permanently added 'ci-mystique.my-tail-net.ts.net' (ED25519) to the list of known hosts.
[philprime@ci-mystique ~]$

Setting up the vSwitch

Since we’re running K3s on bare-metal servers, we need to configure private networking manually. Hetzner provides vSwitch functionality that allows servers to communicate over a private VLAN, isolated from the public internet. This is essential for secure cluster communication.

Navigate to Hetzner Robot, select your server, and click on the “vSwitches” button to access the vSwitches Overview.

If you already have a vSwitch configured (as we do for our existing cluster), click “Manage” next to it. Otherwise, create a new vSwitch by clicking “Create vSwitch” and following the prompts.

Make note of your vSwitch’s VLAN ID - you’ll need this for network configuration later. In our setup, we use VLAN ID 4000.

Add the new server to the vSwitch by selecting it from the “Add Server to vSwitch” dropdown. The connection process typically takes 30-40 seconds, though it can take up to 2-3 minutes in practice. Once complete, verify that your server appears in the list of connected servers.

Setting up the Firewall Rules

NOTE: This configuration is tailored to our specific use case and may need adjustments based on your requirements. It's also subject to change as we further refine our setup.

Hetzner provides network-level firewall functionality that’s more secure than relying solely on host-based iptables rules. We’ll configure restrictive firewall rules to minimize the attack surface while allowing necessary cluster communication.

Navigate to the Server Overview and click “Firewall” next to your server. By default, Hetzner configures two permissive rules that allow all incoming and outgoing traffic:

Rules (incoming):

ID Name Version Protocol Source IP Destination IP Source Port Destination Port TCP Flags Action
#1 all * *           Allow

Rules (outgoing):

ID Name Version Protocol Source IP Destination IP Source Port Destination Port TCP Flags Action
#1 all * *           Allow

We’ll replace the default permissive rules with a more restrictive configuration that only allows necessary traffic:

Rules (incoming):

ID Name Version Protocol Source IP Destination IP Source Port Destination Port TCP Flags Action
#1 icmp ipv4 ICMP           Allow
#2 ssh ipv4 TCP       22   Allow
#3 tcp established ipv4 TCP       1024-65535 ack Allow
#4 dns responses ipv4 UDP 53     1024-65535   Allow
#5 k3s api ipv4 TCP       6443   Allow
#6 tailscale ipv4 UDP       41641   Allow

Here’s what each rule does:

  • Rule #1 (ICMP):

    Enables ping and basic network diagnostics.

  • Rule #2 (SSH):

    Allows remote administration on TCP port 22.

  • Rule #3 (TCP established):

    Accepts inbound TCP packets with ACK targeting ephemeral ports (1024–65535). This correctly handles all return traffic from outbound connections (HTTPS, HTTP, container pull operations, APIs, etc.). It replaces the previous two fragmented return-traffic rules.

  • Rule #4 (DNS responses):

    Permits DNS replies (source port 53) to reach the server’s ephemeral ports.

  • Rule #5 (K3s API):

    Opens port 6443 for Kubernetes API server communication.

  • Rule #6 (Tailscale):

    Allows inbound Tailscale UDP traffic on port 41641.

After configuring these rules, click “Save Changes” to apply them. The changes typically take 30-40 seconds to propagate.

Configuring the vSwitch Network Interface

With the firewall rules in place, we need to configure the network interface for cluster communication. We’ll create a VLAN interface that corresponds to our vSwitch configuration, allowing the node to communicate with other cluster members over the private network (10.0.0.0/24).

First, check the current network configuration:

$ ip addr show
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
2: enp35s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP group default qlen 1000
    link/ether a8:a1:59:xx:xx:xx brd ff:ff:ff:ff:ff:ff
    inet 203.0.113.10/32 scope global noprefixroute enp35s0
       valid_lft forever preferred_lft forever

We’ll create a VLAN interface (enp35s0.4000) on the physical interface with VLAN ID 4000 and assign it IP address 10.0.0.3/24. Rocky Linux 10 uses NetworkManager, so we’ll use nmcli for configuration:

$ sudo nmcli connection add type vlan \
  con-name vswitch0 \
  ifname enp35s0.4000 \
  dev enp35s0 \
  id 4000 \
  ip4 10.0.0.3/24
Connection 'vswitch0' (12345678-1234-1234-1234-123456789abc) successfully added.

Activate the VLAN connection:

$ sudo nmcli connection up vswitch0
Connection successfully activated (D-Bus active path: /org/freedesktop/NetworkManager/ActiveConnection/3)

Verify the interface is configured correctly:

$ ip addr show enp35s0.4000
4: enp35s0.4000@enp35s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
    link/ether a8:a1:59:0f:2b:69 brd ff:ff:ff:ff:ff:ff
    inet 10.0.0.3/24 brd 10.0.0.255 scope global noprefixroute enp35s0.4000 # <-- This interface was added
       valid_lft forever preferred_lft forever
    inet6 fe80::2/64 scope link noprefixroute
       valid_lft forever preferred_lft forever

You can also inspect the connection details to verify the configuration:

$ nmcli connection show vswitch0 | grep -E '(vlan\.|ipv4\.)' | head -10
vlan.parent:                            enp35s0
vlan.id:                                4000
ipv4.method:                            manual
ipv4.addresses:                         10.0.0.3/24
ipv4.gateway:                           --

Test connectivity to verify the private network is working:

# Ping master node
$ ping -c 3 10.0.0.1
PING 10.0.0.1 (10.0.0.1) 56(84) bytes of data.
64 bytes from 10.0.0.1: icmp_seq=1 ttl=64 time=0.234 ms
64 bytes from 10.0.0.1: icmp_seq=2 ttl=64 time=0.198 ms
64 bytes from 10.0.0.1: icmp_seq=3 ttl=64 time=0.201 ms

# Ping another agent node
$ ping -c 3 10.0.0.2
PING 10.0.0.2 (10.0.0.2) 56(84) bytes of data.
64 bytes from 10.0.0.2: icmp_seq=1 ttl=64 time=0.312 ms
64 bytes from 10.0.0.2: icmp_seq=2 ttl=64 time=0.287 ms
64 bytes from 10.0.0.2: icmp_seq=3 ttl=64 time=0.298 ms

Perfect! The VLAN interface is configured and communicating with other cluster nodes. NetworkManager will ensure this configuration persists across reboots.

Installing K3s on the new node

Now we’re ready to install K3s and join the node to our cluster. First, retrieve the join token from an existing master node:

$ ssh master-node-1.ci.example.com
$ sudo cat /var/lib/rancher/k3s/server/node-token
K102f0621c...

Write this token down - you’ll need it for the installation and configuration steps.

Installing K3s with the install script

Run the K3s installation script with minimal parameters. We’ll configure the node-specific settings via config files afterward for better maintainability:

$ curl -sfL https://get.k3s.io | K3S_URL=https://10.0.0.1:6443 K3S_TOKEN=K102f0621c... sh -

When K3S_URL is set, K3s automatically installs in agent mode. The script will download the K3s binary, set up the systemd service, and start the agent. This process will also install any additional services required for K3s operation, such as containerd.

Configuring the node with config files

After installation, we’ll use configuration files to define node settings. This approach is cleaner than command-line arguments and makes future updates easier:

$ sudo mkdir -p /etc/rancher/k3s/config.yaml.d
$ sudo vim /etc/rancher/k3s/config.yaml.d/10-agent.yaml

Add the following configuration (replace token and IPs with your values):

# Join the server over the VLAN
server: https://10.0.0.1:6443
token: K102f0621c...

# Node identity & internal addressing
node-name: ci-mystique
node-ip: 10.0.0.3
node-external-ip:
  - 203.0.113.10
  - fe80::1

# Keep all cluster traffic on the vSwitch (VLAN 4000)
flannel-iface: enp35s0.4000

# Use direct connection to control plane
disable-apiserver-lb: true

Configuration breakdown:

  • server: The K3s server URL using the vSwitch IP
  • token: The join token from the master node
  • node-name: Unique name for this node
  • node-ip: The vSwitch IP for internal cluster communication
  • node-external-ip: The public IP address(es) of this node (IPv4 and IPv6)
  • flannel-iface: Network interface for pod networking (vSwitch VLAN interface)
  • disable-apiserver-lb: Use direct connection instead of the embedded load balancer

Critical: Clean up the systemd service file

The install script embeds command-line arguments directly into the systemd service file. If you create a config file with the same parameters, K3s will see them twice, causing errors like:

bad --node-ip "10.0.0.3,10.0.0.3": must contain either a single IP or a dual-stack pair of IPs

Edit the systemd service file:

$ sudo vim /etc/systemd/system/k3s-agent.service

Find the ExecStart section and remove all hardcoded arguments, leaving only:

ExecStartPre=-/sbin/modprobe br_netfilter
ExecStartPre=-/sbin/modprobe overlay
ExecStart=/usr/local/bin/k3s \
    agent \
CRITICAL: Must run daemon-reload After editing the systemd service file, you MUST run "systemctl daemon-reload" before restarting the service. Without this step, systemd will continue using the old cached service definition, and your changes will not take effect.

After editing, reload the systemd configuration and restart:

$ sudo systemctl daemon-reload
$ sudo systemctl restart k3s-agent

Verify the service is running:

$ sudo systemctl status k3s-agent
● k3s-agent.service - Lightweight Kubernetes
     Loaded: loaded (/etc/systemd/system/k3s-agent.service; enabled; vendor preset: disabled)
     Active: active (running) since Sat 2025-11-23 18:15:20 UTC; 10s ago

From the master node, verify the new node has joined the cluster:

$ kubectl get nodes
NAME           STATUS   ROLES                  AGE   VERSION
ci-kang        Ready    control-plane,master   30d   v1.28.5+k3s1
ci-juggernaut  Ready    <none>                 15d   v1.28.5+k3s1
ci-mystique    Ready    <none>                 2m    v1.28.5+k3s1

Note: You can find the stored token on the agent node at /var/lib/rancher/k3s/agent/token if needed.

Optional: Set up kubectl access for the new node

To manage the new node directly with kubectl, we can set up a kubeconfig file.

You can find the file at /etc/rancher/k3s/k3s.yaml on the existing master node and copy it to your new node (e.g. using scp).

Afterwards make sure to replace the server address in the kubeconfig file to point to the vSwitch IP of the master node (e.g. 10.0.0.1).

Optional: Preserve resources for system

To ensure that the host system has enough resources to perform tasks even with full cluster load, we can reserve some CPU and memory for the system.

Create a new file /etc/rancher/k3s/config.yaml.d/00-reserve-system-resources.yaml with the following content:

kubelet-arg:
  - "system-reserved=cpu=500m,memory=2048Mi"
  - "kube-reserved=cpu=500m,memory=2048Mi"

By reserving 500m CPU and 2048Mi memory for both system and kubelet, we ensure that the host system remains responsive even under high load from pods.

Verifying network connectivity from pods

To ensure that pods running on the new node can access external services, DNS resolution works correctly, and cluster networking is properly configured, we’ll run a test pod with network tools directly on the new node.

First, create a test pod with a node selector to ensure it runs on our new node:

$ kubectl run nettest --image=nicolaka/netshoot --restart=Never \
  --overrides='{"spec":{"nodeSelector":{"kubernetes.io/hostname":"ci-mystique"}}}' \
  -- sleep infinity
pod/nettest created

Wait for the pod to be running:

$ kubectl get pod nettest -o wide
NAME      READY   STATUS    RESTARTS   AGE   IP           NODE          NOMINATED NODE   READINESS GATES
nettest   1/1     Running   0          10s   10.42.2.5    ci-mystique   <none>           <none>

Now let’s verify various network connectivity scenarios:

Test 1: DNS resolution

$ kubectl exec -it nettest -- nslookup example.com
;; Got recursion not available from 10.43.0.10
;; Got recursion not available from 10.43.0.10
;; Got recursion not available from 10.43.0.10
Server:         10.43.0.10
Address:        10.43.0.10#53

Non-authoritative answer:
Name:   example.com
Address: 23.192.228.84
...

The “recursion not available” warnings are non-critical and typically appear when CoreDNS initially processes the query. The important part is that DNS resolution succeeds.

This confirms that:

  • CoreDNS is accessible from the pod (10.43.0.10 is the cluster DNS service)
  • DNS queries can reach external DNS servers
  • The firewall rule #4 (DNS responses) is working correctly

Test 2: HTTP/HTTPS connectivity

Let’s test if we can establish HTTP connections from the pod:

$ kubectl exec -it nettest -- curl -I http://example.com
HTTP/1.1 200 OK
Content-Type: text/html
ETag: "bc2473a18e003bdb249eba5ce893033f:1760028122.592274"
Last-Modified: Thu, 09 Oct 2025 16:42:02 GMT
Cache-Control: max-age=86000
Date: Sun, 23 Nov 2025 17:42:23 GMT
Connection: keep-alive

HTTP works! Now let’s try HTTPS:

$ kubectl exec -it nettest -- curl -I https://example.com
# This might hang or timeout...

Troubleshooting: IPv6 connectivity issue

If HTTPS hangs while HTTP works, let’s check what’s happening:

$ kubectl exec -it nettest -- timeout 5 curl -v https://example.com 2>&1 | head -20
* Host example.com:443 was resolved.
* IPv6: 2600:1406:5e00:6::17ce:bc1b, 2600:1406:bc00:53::b81e:94c8, ...
* IPv4: 23.220.75.245, 23.192.228.84, ...
*   Trying [2600:1406:5e00:6::17ce:bc1b]:443...
* Immediate connect fail for 2600:1406:5e00:6::17ce:bc1b: Network unreachable
*   Trying [2600:1406:bc00:53::b81e:94c8]:443...
* Immediate connect fail for 2600:1406:bc00:53::b81e:94c8: Network unreachable
...
*   Trying 23.220.75.245:443...
command terminated with exit code 143

The issue is clear: curl tries IPv6 addresses first, but IPv6 is not configured in our cluster. Each IPv6 attempt times out before falling back to IPv4, causing the command to hang.

Solution: Force IPv4

Use the -4 flag to force IPv4:

$ kubectl exec -it nettest -- curl -4 -I https://example.com
HTTP/2 200
content-type: text/html
etag: "bc2473a18e003bdb249eba5ce893033f:1760028122.592274"
last-modified: Thu, 09 Oct 2025 16:42:02 GMT
cache-control: max-age=86000
date: Sun, 23 Nov 2025 17:41:04 GMT

Success! Let’s also verify the pod’s network configuration:

$ kubectl exec -it nettest -- ip addr show
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
2: eth0@if13: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default
    link/ether 7a:94:f6:56:8e:35 brd ff:ff:ff:ff:ff:ff link-netnsid 0
    inet 10.42.2.9/24 brd 10.42.2.255 scope global eth0
       valid_lft forever preferred_lft forever

$ kubectl exec -it nettest -- ip route
default via 10.42.2.1 dev eth0
10.42.0.0/16 via 10.42.2.1 dev eth0
10.42.2.0/24 dev eth0 proto kernel scope link src 10.42.2.9

$ kubectl exec -it nettest -- ping -c 3 10.42.2.1
PING 10.42.2.1 (10.42.2.1) 56(84) bytes of data.
64 bytes from 10.42.2.1: icmp_seq=1 ttl=64 time=0.054 ms
64 bytes from 10.42.2.1: icmp_seq=2 ttl=64 time=0.031 ms
64 bytes from 10.42.2.1: icmp_seq=3 ttl=64 time=0.024 ms

--- 10.42.2.1 ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2081ms
rtt min/avg/max/mdev = 0.024/0.036/0.054/0.012 ms

The pod gets an IP from the Flannel overlay network (10.42.x.x range) and can reach its gateway.

Verify the node itself can also make HTTPS connections:

# On the node (ci-mystique)
$ curl -I https://example.com
HTTP/2 200
content-type: text/html
etag: "bc2473a18e003bdb249eba5ce893033f:1760028122.592274"
...

This confirms:

  • HTTP and HTTPS traffic work correctly from pods (using IPv4)
  • DNS resolution is functioning
  • Pod networking and routing are properly configured
  • The firewall rules allow outbound connections and return traffic

Test 3: Internal cluster communication

Test connectivity to the Kubernetes API server:

$ kubectl exec -it nettest -- curl -k https://10.0.0.1:6443
{
  "kind": "Status",
  "apiVersion": "v1",
  "metadata": {},
  "status": "Failure",
  "message": "forbidden: User \"system:anonymous\" cannot get path \"/\"",
  "reason": "Forbidden",
  "details": {},
  "code": 403
}

The 403 response is expected (anonymous user has no permissions), but it confirms:

  • Network connectivity to the master node over vSwitch works
  • Firewall rule #5 (K3s API) is configured correctly
  • Cluster networking is functional

Test 4: Pod-to-pod communication across nodes

Create a simple nginx pod on another node for testing:

$ kubectl run nginx --image=nginx --restart=Never \
  --overrides='{"spec":{"nodeSelector":{"kubernetes.io/hostname":"ci-juggernaut"}}}'
pod/nginx created

$ kubectl get pod nginx -o wide
NAME    READY   STATUS    RESTARTS   AGE   IP          NODE            NOMINATED NODE   READINESS GATES
nginx   1/1     Running   0          5s    10.42.1.8   ci-juggernaut   <none>           <none>

Test connectivity from our nettest pod to the nginx pod:

$ kubectl exec -it nettest -- curl -I http://10.42.1.8
HTTP/1.1 200 OK
Server: nginx/1.25.3
Date: Sat, 23 Nov 2025 18:30:15 GMT
Content-Type: text/html
...

This confirms:

  • Pod-to-pod communication across nodes works
  • Flannel overlay network is functioning correctly
  • Firewall rule #6 (pod return traffic) is properly configured

Test 5: Service discovery

Test accessing a service by DNS name:

$ kubectl expose pod nginx --port=80
service/nginx exposed

$ kubectl exec -it nettest -- curl -I http://nginx.default.svc.cluster.local
HTTP/1.1 200 OK
Server: nginx/1.25.3
...

This validates:

  • Kubernetes service discovery works
  • CoreDNS can resolve cluster service names
  • Service networking (kube-proxy) is functional

Cleanup

After verifying connectivity, clean up the test resources:

$ kubectl delete pod nettest nginx
pod "nettest" deleted
pod "nginx" deleted

$ kubectl delete service nginx
service "nginx" deleted

All network connectivity tests passed successfully, confirming that the new node is properly integrated into the cluster with correct firewall rules and network configuration.

Conclusion

We’ve successfully added a new K3s agent node to our existing bare-metal cluster on Hetzner. The node is now fully operational and ready to run workloads. Remember that this cluster is configured for IPv4-only networking, which is standard practice for bare-metal setups. Applications will work fine, though some tools like curl may attempt IPv6 connections first before falling back to IPv4.