L7 Load Balancing and URL re-writing

Cilium Service Mesh defines a CiliumEnvoyConfig CRD which allows users to set the configuration of the Envoy component built into Cilium agents.

This example sets up an Envoy listener which load balances requests between two backend services.

Deploy Test Applications

$ kubectl apply -f https://raw.githubusercontent.com/cilium/cilium/1.15.4/examples/kubernetes/servicemesh/envoy/test-application.yaml

The test workloads consist of:

  • two client deployments, client and client2

  • two services, echo-service-1 and echo-service-2

View information about these pods:

$ kubectl get pods --show-labels -o wide
NAME                              READY   STATUS    RESTARTS   AGE    IP          NODE           NOMINATED NODE   READINESS GATES   LABELS
client-7568bc7f86-dlfqr           1/1     Running   0          100s   10.0.1.8    minikube-m02   <none>           <none>            kind=client,name=client,pod-template-hash=7568bc7f86
client2-8b4c4fd75-xn25d           1/1     Running   0          100s   10.0.1.24   minikube-m02   <none>           <none>            kind=client,name=client2,other=client,pod-template-hash=8b4c4fd75
echo-service-1-97748874-4sztx     2/2     Running   0          100s   10.0.1.86   minikube-m02   <none>           <none>            kind=echo,name=echo-service-1,other=echo,pod-template-hash=97748874
echo-service-2-76c584c4bf-p4z4w   2/2     Running   0          100s   10.0.1.16   minikube-m02   <none>           <none>            kind=echo,name=echo-service-2,pod-template-hash=76c584c4bf

You can see that

  • Only client2 is labeled with other=client - we will use this in a CiliumNetworkPolicy definition later in this example.

Make an environment variable with the pod ID for client2:

$ export CLIENT2=$(kubectl get pods -l name=client2 -o jsonpath='{.items[0].metadata.name}')

We are going to use Envoy configuration to load-balance requests between these two services echo-service-1 and echo-service-2.

Start Observing Traffic with Hubble

Enable Hubble in your cluster with the step mentioned in Setting up Hubble Observability.

Start a second terminal, then enable hubble port forwarding and observe traffic from the client2 pod:

$ kubectl -n kube-system port-forward deployment/hubble-relay 4245:4245 &
$ hubble observe --from-pod $CLIENT2 -f

You should be able to get a response from both of the backend services individually from client2:

$ kubectl exec -it $CLIENT2 -- curl -v echo-service-1:8080/
$ kubectl exec -it $CLIENT2 -- curl -v echo-service-2:8080/

Notice that Hubble shows all the flows between these pods as being either to/from-stack, to/from-overlay or to/from-endpoint - there is no traffic marked as flowing to or from the proxy at this stage. (This assumes you don’t already have any Layer 7 policies in place affecting this traffic.)

Verify that you get a 404 error response if you curl to the non-existent URL /foo on these services:

$ kubectl exec -it $CLIENT2 -- curl -v echo-service-1:8080/foo
$ kubectl exec -it $CLIENT2 -- curl -v echo-service-2:8080/foo

Add Layer 7 Policy

Adding a Layer 7 policy introduces the Envoy proxy into the path for this traffic.

$ kubectl apply -f https://raw.githubusercontent.com/cilium/cilium/1.15.4/examples/kubernetes/servicemesh/envoy/client-egress-l7-http.yaml
$ kubectl apply -f https://raw.githubusercontent.com/cilium/cilium/1.15.4/examples/kubernetes/servicemesh/envoy/client-egress-only-dns.yaml

Make a request to a backend service (either will do):

$ kubectl exec -it $CLIENT2 -- curl -v echo-service-1:8080/
$ kubectl exec -it $CLIENT2 -- curl -v echo-service-2:8080/foo

Adding a Layer 7 policy enables Layer 7 visibility. Notice that the Hubble output now includes flows to-proxy, and also shows the HTTP protocol information at level 7 (for example HTTP/1.1 GET http://echo-service-1:8080/)

Test Layer 7 Policy Enforcement

The policy only permits GET requests to the / path, so you will see requests to any other URL being dropped. For example, try:

$ kubectl exec -it $CLIENT2 -- curl -v echo-service-1:8080/foo

The Hubble output will show the HTTP request being dropped, like this:

Jul  7 08:40:15.076: default/client2-8b4c4fd75-6pgvl:58586 -> default/echo-service-1-97748874-n7758:8080 http-request DROPPED (HTTP/1.1 GET http://echo-service-1:8080/foo)

And the curl should show a 403 Forbidden response.

Add Envoy load-balancing and URL re-writing

Apply the envoy-traffic-management-test.yaml file, which defines a CiliumClusterwideEnvoyConfig.

$ kubectl apply -f https://raw.githubusercontent.com/cilium/cilium/1.15.4/examples/kubernetes/servicemesh/envoy/envoy-traffic-management-test.yaml

Note

Note that these Envoy resources are not validated by K8s at all, so any errors in the Envoy resources will only be seen by the Cilium Agent observing these CRDs. This means that kubectl apply will report success, while parsing and/or installing the resources for the node-local Envoy instance may have failed. Currently the only way of verifying this is by observing Cilium Agent logs for errors and warnings. Additionally, Cilium Agent will print warning logs for any conflicting Envoy resources in the cluster.

Note

Note that Cilium Ingress Controller will configure required Envoy resource under the hood. Please check Cilium Agent logs if you are creating Envoy resources explicitly to make sure there is no conflict.

This configuration listens for traffic intended for either of the two echo- services and:

  • load-balances 50/50 between the two backend echo- services

  • rewrites the path /foo to /

A request to /foo should now succeed, because of the path re-writing:

$ kubectl exec -it $CLIENT2 -- curl -v echo-service-1:8080/foo

But the network policy still prevents requests to any path that is not rewritten to /. For example, this request will result in a packet being dropped and a 403 Forbidden response code:

$ kubectl exec -it $CLIENT2 -- curl -v echo-service-1:8080/bar

### Output from hubble observe
Jul  7 08:43:47.165: default/client2-8b4c4fd75-6pgvl:33376 -> default/echo-service-2-76c584c4bf-874dm:8080 http-request DROPPED (HTTP/1.1 GET http://echo-service-1:8080/bar)

Try making several requests to one backend service. You should see in the Hubble output approximately half the time, they are handled by the other backend.

Example:

Jul  7 08:45:25.807: default/client2-8b4c4fd75-6pgvl:37388 -> kube-system/coredns-64897985d-8jhhn:53 L3-L4 REDIRECTED (UDP)
Jul  7 08:45:25.807: default/client2-8b4c4fd75-6pgvl:37388 -> kube-system/coredns-64897985d-8jhhn:53 to-proxy FORWARDED (UDP)
Jul  7 08:45:25.807: default/client2-8b4c4fd75-6pgvl:37388 -> kube-system/coredns-64897985d-8jhhn:53 dns-request FORWARDED (DNS Query echo-service-1.default.svc.cluster.local. AAAA)
Jul  7 08:45:25.807: default/client2-8b4c4fd75-6pgvl:37388 -> kube-system/coredns-64897985d-8jhhn:53 dns-request FORWARDED (DNS Query echo-service-1.default.svc.cluster.local. A)
Jul  7 08:45:25.808: default/client2-8b4c4fd75-6pgvl:57942 -> default/echo-service-1:8080 none REDIRECTED (TCP Flags: SYN)
Jul  7 08:45:25.808: default/client2-8b4c4fd75-6pgvl:57942 -> default/echo-service-1:8080 to-proxy FORWARDED (TCP Flags: SYN)
Jul  7 08:45:25.808: default/client2-8b4c4fd75-6pgvl:57942 -> default/echo-service-1:8080 to-proxy FORWARDED (TCP Flags: ACK)
Jul  7 08:45:25.808: default/client2-8b4c4fd75-6pgvl:57942 -> default/echo-service-1:8080 to-proxy FORWARDED (TCP Flags: ACK, PSH)
Jul  7 08:45:25.809: default/client2-8b4c4fd75-6pgvl:57942 -> default/echo-service-2-76c584c4bf-874dm:8080 L3-L4 REDIRECTED (TCP Flags: SYN)
Jul  7 08:45:25.809: default/client2-8b4c4fd75-6pgvl:57942 -> default/echo-service-2-76c584c4bf-874dm:8080 to-endpoint FORWARDED (TCP Flags: SYN)
Jul  7 08:45:25.809: default/client2-8b4c4fd75-6pgvl:57942 -> default/echo-service-2-76c584c4bf-874dm:8080 to-endpoint FORWARDED (TCP Flags: ACK)
Jul  7 08:45:25.809: default/client2-8b4c4fd75-6pgvl:57942 -> default/echo-service-2-76c584c4bf-874dm:8080 to-endpoint FORWARDED (TCP Flags: ACK, PSH)
Jul  7 08:45:25.809: default/client2-8b4c4fd75-6pgvl:57942 -> default/echo-service-2-76c584c4bf-874dm:8080 http-request FORWARDED (HTTP/1.1 GET http://echo-service-1:8080/)
Jul  7 08:45:25.811: default/client2-8b4c4fd75-6pgvl:57942 -> default/echo-service-1:8080 to-proxy FORWARDED (TCP Flags: ACK, FIN)
Jul  7 08:45:25.811: default/client2-8b4c4fd75-6pgvl:57942 -> default/echo-service-1:8080 to-proxy FORWARDED (TCP Flags: ACK)
Jul  7 08:45:30.811: default/client2-8b4c4fd75-6pgvl:57942 -> default/echo-service-2-76c584c4bf-874dm:8080 to-endpoint FORWARDED (TCP Flags: ACK, FIN)