Relay Cluster

Running basic connectivity between nginx server and client through a relay cluster using ClusterLink.

This task involves creating multi-hop connectivity between a client and a server using relay clusters. Multi-hop connectivity using a relay may be necessary for several reasons, such as:

When the client needs to use an indirect connection due to network path limitations.
Using multiple relays allows for explicit selection between multiple network paths without impacting or changing the underlying routing information.
Using multiple relays provides failover for the network paths.

In this task, we’ll establish multi-hop connectivity across clusters using ClusterLink to access a remote nginx server. In this case, the client will not access the service directly in the server cluster but will pass through a relay cluster. The example uses three clusters:

Client cluster - runs ClusterLink along with a client.
Relay cluster - runs ClusterLink and connects the services between the client and the server.
Server cluster - runs ClusterLink along with an nginx server.

System illustration:

Run basic nginx Tutorial

This is an extension of the basic nginx toturial. Please run it first and set up the nginx server and client cluster.

Create relay Cluster with ClusterLink

Open third terminal for the relay cluster:
Relay cluster:
```
cd nginx-tutorial
kind create cluster --name=relay
```

Setup KUBECONFIG the relay cluster:

Relay cluster:

kubectl config use-context kind-relay
cp ~/.kube/config $PWD/config-relay
export KUBECONFIG=$PWD/config-relay

Create peer certificates for the relay:
Relay cluster:
```
clusterlink create peer-cert --name relay
```
Note
The relay cluster certificates should use the same Fabric CA files as the server and the client.

Deploy ClusterLink on the relay cluster:

Relay cluster:

clusterlink deploy peer --name relay --ingress=NodePort --ingress-port=30443

Enable cross-cluster access using the relay

Establish connectivity between the relay and the server by adding the server peer, importing the nginx service from the server, and adding the allow policy.

Relay cluster:

export TEST_FILES=https://raw.githubusercontent.com/clusterlink-net/clusterlink/main/demos/nginx/testdata
export SERVER_IP=`docker inspect -f '{{range .NetworkSettings.Networks}}{{.IPAddress}}{{end}}' server-control-plane`
curl -s $TEST_FILES/clusterlink/peer-server.yaml | envsubst | kubectl apply -f -
kubectl apply -f $TEST_FILES/clusterlink/import-nginx.yaml
kubectl apply -f $TEST_FILES/clusterlink/allow-policy.yaml

Establish connectivity between the relay and the client by adding the relay peer to the client cluster, exporting the nginx service in the relay, and importing it into the client.

Relay cluster:

kubectl apply -f $TEST_FILES/clusterlink/export-nginx.yaml

Client cluster:

export TEST_FILES=https://raw.githubusercontent.com/clusterlink-net/clusterlink/main/demos/nginx/testdata
export RELAY_IP=`docker inspect -f '{{range .NetworkSettings.Networks}}{{.IPAddress}}{{end}}' relay-control-plane`
curl -s $TEST_FILES/clusterlink/peer-relay.yaml | envsubst | kubectl apply -f -
kubectl apply -f $TEST_FILES/clusterlink/import-nginx-relay.yaml

Test service connectivity

Test the connectivity between the clusters (through the relay) with a batch job of the curl command:

Client cluster:

kubectl apply -f $TEST_FILES/nginx-relay-job.yaml

Verify the job succeeded:

kubectl logs jobs/curl-nginx-relay-homepage

Sample output

  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
<!DOCTYPE html>
<html>
<head>
<title>Welcome to nginx!</title>
<style>
html { color-scheme: light dark; }
body { width: 35em; margin: 0 auto;
font-family: Tahoma, Verdana, Arial, sans-serif; }
</style>
</head>
<body>
<h1>Welcome to nginx!</h1>
<p>If you see this page, the nginx web server is successfully installed and
working. Further configuration is required.</p>

<p>For online documentation and support please refer to
<a href="http://nginx.org/">nginx.org</a>.<br/>
Commercial support is available at
<a href="http://nginx.com/">nginx.com</a>.</p>

<p><em>Thank you for using nginx.</em></p>
</body>
</html>

Cleanup

Delete the kind clusters: Client cluster:

kind delete cluster --name=client

Server cluster:

kind delete cluster --name=server

kind delete cluster --name=relay

Remove the tutorial directory:
```
cd .. && rm -rf nginx-tutorial
```

Unset the environment variables: Client cluster:

unset KUBECONFIG TEST_FILES

Server cluster:

unset KUBECONFIG TEST_FILES

Rekay cluster:

unset KUBECONFIG TEST_FILES

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Last modified July 24, 2024: fix notify note to look as the rest of the notes (79aa28a)