kilo/docs/vpn.md

# VPN

Kilo enables peers outside of a Kubernetes cluster to connect to the created WireGuard network.
This enables several use cases, for example:
* giving cluster applications secure access to external services, e.g. services behind a corporate VPN;
* improving the development flow of applications by running them locally and connecting them to the cluster;
* allowing external services to access the cluster; and
* enabling developers and support to securely debug cluster resources.

In order to declare a peer, start by defining a Kilo Peer resource.
See the following `peer.yaml`, where the `publicKey` field holds a [generated WireGuard public key](https://www.wireguard.com/quickstart/#key-generation):

```yaml
apiVersion: kilo.squat.ai/v1alpha1
kind: Peer
metadata:
  name: squat
spec:
  allowedIPs:
  - 10.5.0.1/32 # Example IP address on the peer's interface.
  publicKey: GY5aT1N9dTR/nJnT1N2f4ClZWVj0jOAld0r8ysWLyjg=
  persistentKeepalive: 10
```

Then, apply the resource to the cluster:

```shell
kubectl apply -f peer.yaml
```

Now, the `kgctl` tool can be used to generate the WireGuard configuration for the newly defined peer:

```shell
PEER=squat
kgctl showconf peer $PEER
```

This will produce some output like:

```ini
[Peer]
PublicKey = 2/xU029dz/WtvMZAbnSzmhicl8U1/Y3NYmunRr8EJ0Q=
AllowedIPs = 10.4.0.2/32, 10.2.3.0/24, 10.1.0.3/32
Endpoint = 108.61.142.123:51820
```

The configuration can then be applied to a local WireGuard interface, e.g. `wg0`:

```shell
IFACE=wg0
kgctl showconf peer $PEER > peer.ini
sudo wg setconf $IFACE peer.ini
```

Finally, in order to access the cluster, the client will need appropriate routes for the new configuration.
For example, on a Linux machine, the creation of these routes could be automated by running:

```shell
for ip in $(kgctl showconf peer $PEER | grep AllowedIPs | cut -f 3- -d ' ' | tr -d ','); do
	sudo ip route add $ip dev $IFACE
done
```

Once the routes are in place, the connection to the cluster can be tested.
For example, try connecting to the API server:

```shell
curl -k https://$(kubectl get endpoints kubernetes | tail -n +2 | tr , \\t | awk '{print $2}')
```

Likewise, the cluster now also has layer 3 access to the newly added peer.
From any node or Pod on the cluster, one can now ping the peer:

```shell
ping 10.5.0.1
```

If the peer exposes a layer 4 service, for example an HTTP server listening on TCP port 80, then one could also make requests against that endpoint from the cluster:

```shell
curl http://10.5.0.1
```

Kubernetes Services can be created to provide better discoverability to cluster workloads for services exposed by peers, for example:

```shell
cat <<'EOF' | kubectl apply -f -
apiVersion: v1
kind: Service
metadata:
  name: important-service
spec:
  ports:
    - port: 80
---
apiVersion: v1
kind: Endpoints
metadata:
    name: important-service
subsets:
  - addresses:
      - ip: 10.5.0.1
    ports:
      - port: 80
EOF
```

[See the multi-cluster services docs for more details on connecting clusters to external services](./multi-cluster-services.md).

Although it is not a primary goal of the project, the VPN created by Kilo can also be [used by peers as a gateway to the Internet; for more details, see the VPN server docs](./vpn-server.md).