Ingress Gateways

Along with support for Kubernetes Ingress resources, Istio also allows you to configure ingress traffic using either an Istio Gateway or Kubernetes Gateway resource. A Gateway provides more extensive customization and flexibility than Ingress, and allows Istio features such as monitoring and route rules to be applied to traffic entering the cluster.

This task describes how to configure Istio to expose a service outside of the service mesh using a Gateway.

Before you begin

  • Setup Istio by following the instructions in the Installation guide.

  • Start the httpbin sample, which will serve as the target service for ingress traffic:

    Zip
    $ kubectl apply -f @samples/httpbin/httpbin.yaml@
    

    Note that for the purpose of this document, which shows how to use a gateway to control ingress traffic into your “Kubernetes cluster”, you can start the httpbin service with or without sidecar injection enabled (i.e., the target service can be either inside or outside of the Istio mesh).

Configuring ingress using a gateway

An ingress Gateway describes a load balancer operating at the edge of the mesh that receives incoming HTTP/TCP connections. It configures exposed ports, protocols, etc. but, unlike Kubernetes Ingress Resources, does not include any traffic routing configuration. Traffic routing for ingress traffic is instead configured using routing rules, exactly in the same way as for internal service requests.

Let’s see how you can configure a Gateway on port 80 for HTTP traffic.

Create an Istio Gateway:

$ kubectl apply -f - <<EOF
apiVersion: networking.istio.io/v1alpha3
kind: Gateway
metadata:
  name: httpbin-gateway
spec:
  selector:
    istio: ingressgateway # use Istio default gateway implementation
  servers:
  - port:
      number: 80
      name: http
      protocol: HTTP
    hosts:
    - "httpbin.example.com"
EOF

Configure routes for traffic entering via the Gateway:

$ kubectl apply -f - <<EOF
apiVersion: networking.istio.io/v1alpha3
kind: VirtualService
metadata:
  name: httpbin
spec:
  hosts:
  - "httpbin.example.com"
  gateways:
  - httpbin-gateway
  http:
  - match:
    - uri:
        prefix: /status
    - uri:
        prefix: /delay
    route:
    - destination:
        port:
          number: 8000
        host: httpbin
EOF

You have now created a virtual service configuration for the httpbin service containing two route rules that allow traffic for paths /status and /delay.

The gateways list specifies that only requests through your httpbin-gateway are allowed. All other external requests will be rejected with a 404 response.

Determining the ingress IP and ports

Every Gateway is backed by a service of type LoadBalancer. The external load balancer IP and ports for this service are used to access the gateway. Kubernetes services of type LoadBalancer are supported by default in clusters running on most cloud platforms but in some environments (e.g., test) you may need to do the following:

  • minikube - start an external load balancer by running the following command in a different terminal:

    $ minikube tunnel
    
  • kind - follow the guide for setting up MetalLB to get LoadBalancer type services to work.

  • other platforms - you may be able to use MetalLB to get an EXTERNAL-IP for LoadBalancer services.

For convenience, we will store the ingress IP and ports in environment variables which will be used in later instructions. Set the INGRESS_HOST and INGRESS_PORT environment variables according to the following instructions:

If you are unsure, you can determine if your Kubernetes cluster is running in an environment that supports external load balancers using the following command:

$ kubectl get svc istio-ingressgateway -n istio-system
NAME                   TYPE           CLUSTER-IP       EXTERNAL-IP      PORT(S)   AGE
istio-ingressgateway   LoadBalancer   172.21.109.129   130.211.10.121   ...       17h

If the EXTERNAL-IP value is set, your environment has an external load balancer that you can use for the ingress gateway. If the EXTERNAL-IP value is <none> (or perpetually <pending>), your environment does not provide an external load balancer for the ingress gateway.

If your environment does not support external load balancers, you can try accessing the ingress gateway using node ports. Otherwise, set the ingress IP and ports using the following commands:

$ export INGRESS_HOST=$(kubectl -n istio-system get service istio-ingressgateway -o jsonpath='{.status.loadBalancer.ingress[0].ip}')
$ export INGRESS_PORT=$(kubectl -n istio-system get service istio-ingressgateway -o jsonpath='{.spec.ports[?(@.name=="http2")].port}')
$ export SECURE_INGRESS_PORT=$(kubectl -n istio-system get service istio-ingressgateway -o jsonpath='{.spec.ports[?(@.name=="https")].port}')
$ export TCP_INGRESS_PORT=$(kubectl -n istio-system get service istio-ingressgateway -o jsonpath='{.spec.ports[?(@.name=="tcp")].port}')

Accessing ingress services

  1. Access the httpbin service using curl:

    $ curl -s -I -HHost:httpbin.example.com "http://$INGRESS_HOST:$INGRESS_PORT/status/200"
    HTTP/1.1 200 OK
    server: istio-envoy
    ...
    

    Note that you use the -H flag to set the Host HTTP header to “httpbin.example.com”. This is needed because your ingress Gateway is configured to handle “httpbin.example.com”, but in your test environment you have no DNS binding for that host and are simply sending your request to the ingress IP.

  2. Access any other URL that has not been explicitly exposed. You should see an HTTP 404 error:

    $ curl -s -I -HHost:httpbin.example.com "http://$INGRESS_HOST:$INGRESS_PORT/headers"
    HTTP/1.1 404 Not Found
    ...
    

Accessing ingress services using a browser

Entering the httpbin service URL in a browser won’t work because you can’t pass the Host header to a browser like you did with curl. In a real world situation, this is not a problem because you configure the requested host properly and DNS resolvable. Thus, you use the host’s domain name in the URL, for example, https://httpbin.example.com/status/200.

You can work around this problem for simple tests and demos as follows:

Use a wildcard * value for the host in the Gateway and VirtualService configurations. For example, change your ingress configuration to the following:

$ kubectl apply -f - <<EOF
apiVersion: networking.istio.io/v1alpha3
kind: Gateway
metadata:
  name: httpbin-gateway
spec:
  selector:
    istio: ingressgateway # use Istio default gateway implementation
  servers:
  - port:
      number: 80
      name: http
      protocol: HTTP
    hosts:
    - "*"
---
apiVersion: networking.istio.io/v1alpha3
kind: VirtualService
metadata:
  name: httpbin
spec:
  hosts:
  - "*"
  gateways:
  - httpbin-gateway
  http:
  - match:
    - uri:
        prefix: /headers
    route:
    - destination:
        port:
          number: 8000
        host: httpbin
EOF

You can then use $INGRESS_HOST:$INGRESS_PORT in the browser URL. For example, http://$INGRESS_HOST:$INGRESS_PORT/headers will display all the headers that your browser sends.

Understanding what happened

The Gateway configuration resources allow external traffic to enter the Istio service mesh and make the traffic management and policy features of Istio available for edge services.

In the preceding steps, you created a service inside the service mesh and exposed an HTTP endpoint of the service to external traffic.

Using node ports of the ingress gateway service

If your environment does not support external load balancers, you can still experiment with some of the Istio features by using the istio-ingressgateway service’s node ports.

Set the ingress ports:

$ export INGRESS_PORT=$(kubectl -n istio-system get service istio-ingressgateway -o jsonpath='{.spec.ports[?(@.name=="http2")].nodePort}')
$ export SECURE_INGRESS_PORT=$(kubectl -n istio-system get service istio-ingressgateway -o jsonpath='{.spec.ports[?(@.name=="https")].nodePort}')
$ export TCP_INGRESS_PORT=$(kubectl -n istio-system get service istio-ingressgateway -o jsonpath='{.spec.ports[?(@.name=="tcp")].nodePort}')

Setting the ingress IP depends on the cluster provider:

  1. GKE:

    $ export INGRESS_HOST=worker-node-address
    

    You need to create firewall rules to allow the TCP traffic to the ingressgateway service’s ports. Run the following commands to allow the traffic for the HTTP port, the secure port (HTTPS) or both:

    $ gcloud compute firewall-rules create allow-gateway-http --allow "tcp:$INGRESS_PORT"
    $ gcloud compute firewall-rules create allow-gateway-https --allow "tcp:$SECURE_INGRESS_PORT"
    
  2. IBM Cloud Kubernetes Service:

    $ ibmcloud ks workers --cluster cluster-name-or-id
    $ export INGRESS_HOST=public-IP-of-one-of-the-worker-nodes
    
  3. Docker For Desktop:

    $ export INGRESS_HOST=127.0.0.1
    
  4. Other environments:

    $ export INGRESS_HOST=$(kubectl get po -l istio=ingressgateway -n istio-system -o jsonpath='{.items[0].status.hostIP}')
    

Troubleshooting

  1. Inspect the values of the INGRESS_HOST and INGRESS_PORT environment variables. Make sure they have valid values, according to the output of the following commands:

    $ kubectl get svc -n istio-system
    $ echo "INGRESS_HOST=$INGRESS_HOST, INGRESS_PORT=$INGRESS_PORT"
    
  2. Check that you have no other Istio ingress gateways defined on the same port:

    $ kubectl get gateway --all-namespaces
    
  3. Check that you have no Kubernetes Ingress resources defined on the same IP and port:

    $ kubectl get ingress --all-namespaces
    
  4. If you have an external load balancer and it does not work for you, try to access the gateway using its node port.

Cleanup

Delete the Gateway and VirtualService configuration, and shutdown the httpbin service:

Zip
$ kubectl delete gateway httpbin-gateway
$ kubectl delete virtualservice httpbin
$ kubectl delete --ignore-not-found=true -f @samples/httpbin/httpbin.yaml@
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