Egress using Wildcard Hosts

 7 minute read     page test

The Accessing External Services task and the Configure an Egress Gateway example describe how to configure egress traffic for specific hostnames, like edition.cnn.com. This example shows how to enable egress traffic for a set of hosts in a common domain, for example *.wikipedia.org, instead of configuring each and every host separately.

Background

Suppose you want to enable egress traffic in Istio for the wikipedia.org sites in all languages. Each version of wikipedia.org in a particular language has its own hostname, e.g., en.wikipedia.org and de.wikipedia.org in the English and the German languages, respectively. You want to enable egress traffic by common configuration items for all the Wikipedia sites, without the need to specify every language’s site separately.

Before you begin

  • Install Istio with access logging enabled and with the blocking-by-default outbound traffic policy:
$ istioctl install --set profile=demo --set meshConfig.outboundTrafficPolicy.mode=REGISTRY_ONLY

  • Deploy the curl sample app to use as a test source for sending requests. If you have automatic sidecar injection enabled, run the following command to deploy the sample app:

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

    Otherwise, manually inject the sidecar before deploying the curl application with the following command:

    Zip
    $ kubectl apply -f <(istioctl kube-inject -f @samples/curl/curl.yaml@)

  • Set the SOURCE_POD environment variable to the name of your source pod:

    $ export SOURCE_POD=$(kubectl get pod -l app=curl -o jsonpath={.items..metadata.name})

Configure direct traffic to a wildcard host

The first, and simplest, way to access a set of hosts within a common domain is by configuring a simple ServiceEntry with a wildcard host and calling the services directly from the sidecar. When calling services directly (i.e., not via an egress gateway), the configuration for a wildcard host is no different than that of any other (e.g., fully qualified) host, only much more convenient when there are many hosts within the common domain.

  1. Define a ServiceEntry for *.wikipedia.org:

    $ kubectl apply -f - <<EOF
apiVersion: networking.istio.io/v1
kind: ServiceEntry
metadata:
  name: wikipedia
spec:
  hosts:
  - "*.wikipedia.org"
  ports:
  - number: 443
    name: https
    protocol: HTTPS
EOF

  2. Send HTTPS requests to https://en.wikipedia.org and https://de.wikipedia.org:

    $ kubectl exec "$SOURCE_POD" -c curl -- sh -c 'curl -s https://en.wikipedia.org/wiki/Main_Page | grep -o "<title>.*</title>"; curl -s https://de.wikipedia.org/wiki/Wikipedia:Hauptseite | grep -o "<title>.*</title>"'
<title>Wikipedia, the free encyclopedia</title>
<title>Wikipedia – Die freie Enzyklopädie</title>

Cleanup direct traffic to a wildcard host

$ kubectl delete serviceentry wikipedia

Configure egress gateway traffic to a wildcard host

When all wildcard hosts are served by a single server, the configuration for egress gateway-based access to a wildcard host is very similar to that of any host, with one exception: the configured route destination will not be the same as the configured host, i.e., the wildcard. It will instead be configured with the host of the single server for the set of domains.

  1. Create an egress Gateway for *.wikipedia.org and route rules to direct the traffic through the egress gateway and from the egress gateway to the external service:
$ kubectl apply -f - <<EOF
apiVersion: networking.istio.io/v1
kind: Gateway
metadata:
  name: istio-egressgateway
spec:
  selector:
    istio: egressgateway
  servers:
  - port:
      number: 443
      name: https
      protocol: HTTPS
    hosts:
    - "*.wikipedia.org"
    tls:
      mode: PASSTHROUGH
---
apiVersion: networking.istio.io/v1
kind: DestinationRule
metadata:
  name: egressgateway-for-wikipedia
spec:
  host: istio-egressgateway.istio-system.svc.cluster.local
  subsets:
    - name: wikipedia
---
apiVersion: networking.istio.io/v1
kind: VirtualService
metadata:
  name: direct-wikipedia-through-egress-gateway
spec:
  hosts:
  - "*.wikipedia.org"
  gateways:
  - mesh
  - istio-egressgateway
  tls:
  - match:
    - gateways:
      - mesh
      port: 443
      sniHosts:
      - "*.wikipedia.org"
    route:
    - destination:
        host: istio-egressgateway.istio-system.svc.cluster.local
        subset: wikipedia
        port:
          number: 443
      weight: 100
  - match:
    - gateways:
      - istio-egressgateway
      port: 443
      sniHosts:
      - "*.wikipedia.org"
    route:
    - destination:
        host: www.wikipedia.org
        port:
          number: 443
      weight: 100
EOF

  1. Create a ServiceEntry for the destination server, www.wikipedia.org:

    $ kubectl apply -f - <<EOF
apiVersion: networking.istio.io/v1
kind: ServiceEntry
metadata:
  name: www-wikipedia
spec:
  hosts:
  - www.wikipedia.org
  ports:
  - number: 443
    name: https
    protocol: HTTPS
  resolution: DNS
EOF

  2. Send HTTPS requests to https://en.wikipedia.org and https://de.wikipedia.org:

    $ kubectl exec "$SOURCE_POD" -c curl -- sh -c 'curl -s https://en.wikipedia.org/wiki/Main_Page | grep -o "<title>.*</title>"; curl -s https://de.wikipedia.org/wiki/Wikipedia:Hauptseite | grep -o "<title>.*</title>"'
<title>Wikipedia, the free encyclopedia</title>
<title>Wikipedia – Die freie Enzyklopädie</title>

  3. Check the statistics of the egress gateway’s proxy for the counter that corresponds to your requests to *.wikipedia.org:

$ kubectl exec "$(kubectl get pod -l istio=egressgateway -n istio-system -o jsonpath='{.items[0].metadata.name}')" -c istio-proxy -n istio-system -- pilot-agent request GET clusters | grep '^outbound|443||www.wikipedia.org.*cx_total:'
outbound|443||www.wikipedia.org::208.80.154.224:443::cx_total::2

Cleanup egress gateway traffic to a wildcard host

$ kubectl delete serviceentry www-wikipedia
$ kubectl delete gateway istio-egressgateway
$ kubectl delete virtualservice direct-wikipedia-through-egress-gateway
$ kubectl delete destinationrule egressgateway-for-wikipedia

Wildcard configuration for arbitrary domains

The configuration in the previous section worked because all the *.wikipedia.org sites can be served by any one of the wikipedia.org servers. However, this is not always the case. For example, you may want to configure egress control for access to more general wildcard domains like *.com or *.org. Configuring traffic to arbitrary wildcard domains introduces a challenge for Istio gateways; an Istio gateway can only be configured to route traffic to predefined hosts, predefined IP addresses, or to the original destination IP address of the request.

In the previous section you configured the virtual service to direct traffic to the predefined host www.wikipedia.org. In the general case, however, you don’t know the host or IP address that can serve an arbitrary host received in a request, which leaves the original destination address of the request as the only value with which to route the request. Unfortunately, when using an egress gateway, the original destination address of the request is lost since the original request is redirected to the gateway, causing the destination IP address to become the IP address of the gateway.

Although not as easy and somewhat fragile as it relies on Istio implementation details, you can use Envoy filters to configure a gateway to support arbitrary domains by using the SNI value in an HTTPS, or any TLS, request to identify the original destination to which to route the request. One example of this configuration approach can be found in routing egress traffic to wildcard destinations.

Cleanup

  • Shutdown the curl service:

    Zip
    $ kubectl delete -f @samples/curl/curl.yaml@

  • Uninstall Istio from your cluster:

    $ istioctl uninstall --purge -y
Was this information useful?
Do you have any suggestions for improvement?

Thanks for your feedback!