Istio as a Proxy for External Services

Configure Istio ingress gateway to act as a proxy for external services

By Vadim Eisenberg (IBM) | October 15, 2019 | 5 minute read

The Control Ingress Traffic and the Ingress Gateway without TLS Termination tasks describe how to configure an ingress gateway to expose services inside the mesh to external traffic. The services can be HTTP or HTTPS. In the case of HTTPS, the gateway passes the traffic through, without terminating TLS.

This blog post describes how to use the same ingress gateway mechanism of Istio to enable access to external services and not to applications inside the mesh. This way Istio as a whole can serve just as a proxy server, with the added value of observability, traffic management and policy enforcement.

The blog post shows configuring access to an HTTP and an HTTPS external service, namely httpbin.org and edition.cnn.com.

Configure an ingress gateway

Define an ingress gateway with a servers: section configuring the 80 and 443 ports. Ensure mode: is set to PASSTHROUGH for tls: in the port 443, which instructs the gateway to pass the ingress traffic AS IS, without terminating TLS.

$ kubectl apply -f - <<EOF
apiVersion: networking.istio.io/v1alpha3
kind: Gateway
metadata:
  name: proxy
spec:
  selector:
    istio: ingressgateway # use istio default ingress gateway
  servers:
  - port:
      number: 80
      name: http
      protocol: HTTP
    hosts:
    - httpbin.org
  - port:
      number: 443
      name: tls
      protocol: TLS
    tls:
      mode: PASSTHROUGH
    hosts:
    - edition.cnn.com
EOF

Create service entries for the httpbin.org and edition.cnn.com services to make them accessible from the ingress gateway:

$ kubectl apply -f - <<EOF
apiVersion: networking.istio.io/v1alpha3
kind: ServiceEntry
metadata:
  name: httpbin-ext
spec:
  hosts:
  - httpbin.org
  ports:
  - number: 80
    name: http
    protocol: HTTP
  resolution: DNS
  location: MESH_EXTERNAL
---
apiVersion: networking.istio.io/v1alpha3
kind: ServiceEntry
metadata:
  name: cnn
spec:
  hosts:
  - edition.cnn.com
  ports:
  - number: 443
    name: tls
    protocol: TLS
  resolution: DNS
  location: MESH_EXTERNAL
EOF

Create a service entry and configure a destination rule for the localhost service. You need this service entry in the next step as a destination for traffic to the external services from applications inside the mesh to block traffic from inside the mesh. In this example you use Istio as a proxy between external applications and external services.

$ kubectl apply -f - <<EOF
apiVersion: networking.istio.io/v1alpha3
kind: ServiceEntry
metadata:
  name: localhost
spec:
  hosts:
  - localhost.local
  location: MESH_EXTERNAL
  ports:
  - number: 80
    name: http
    protocol: HTTP
  - number: 443
    name: tls
    protocol: TLS
  resolution: STATIC
  endpoints:
  - address: 127.0.0.1
---
apiVersion: networking.istio.io/v1alpha3
kind: DestinationRule
metadata:
  name: localhost
spec:
  host: localhost.local
  trafficPolicy:
    tls:
      mode: DISABLE
      sni: localhost.local
EOF

Create a virtual service for each external service to configure routing to it. Both virtual services include the proxy gateway in the gateways: section and in the match: section for HTTP and HTTPS traffic accordingly.

Notice the route: section for the mesh gateway, the gateway that represents the applications inside the mesh. The route: for the mesh gateway shows how the traffic is directed to the localhost.local service, effectively blocking the traffic.

$ kubectl apply -f - <<EOF
apiVersion: networking.istio.io/v1alpha3
kind: VirtualService
metadata:
  name: httpbin
spec:
  hosts:
  - httpbin.org
  gateways:
  - proxy
  - mesh
  http:
  - match:
    - gateways:
      - proxy
      port: 80
      uri:
        prefix: /status
    route:
    - destination:
        host: httpbin.org
        port:
          number: 80
  - match:
    - gateways:
      - mesh
      port: 80
    route:
    - destination:
        host: localhost.local
        port:
          number: 80
---
apiVersion: networking.istio.io/v1alpha3
kind: VirtualService
metadata:
  name: cnn
spec:
  hosts:
  - edition.cnn.com
  gateways:
  - proxy
  - mesh
  tls:
  - match:
    - gateways:
      - proxy
      port: 443
      sni_hosts:
      - edition.cnn.com
    route:
    - destination:
        host: edition.cnn.com
        port:
          number: 443
  - match:
    - gateways:
      - mesh
      port: 443
      sni_hosts:
      - edition.cnn.com
    route:
    - destination:
        host: localhost.local
        port:
          number: 443
EOF

Enable Envoy’s access logging.
Follow the instructions in Determining the ingress IP and ports to define the SECURE_INGRESS_PORT and INGRESS_HOST environment variables.
Access the httbin.org service through your ingress IP and port which you stored in the $INGRESS_HOST and $INGRESS_PORT environment variables, respectively, during the previous step. Access the /status/418 path of the httpbin.org service that returns the HTTP status 418 I’m a teapot.
```
$ curl $INGRESS_HOST:$INGRESS_PORT/status/418 -Hhost:httpbin.org
-=[ teapot ]=-

   _...._
 .'  _ _ `.
| ."` ^ `". _,
\_;`"---"`|//
  |       ;/
  \_     _/
    `"""`
```
If the Istio ingress gateway is deployed in the istio-system namespace, print the gateway’s log with the following command:
```
$ kubectl logs -l istio=ingressgateway -c istio-proxy -n istio-system | grep 'httpbin.org'
```

Search the log for an entry similar to:

[2019-01-31T14:40:18.645Z] "GET /status/418 HTTP/1.1" 418 - 0 135 187 186 "10.127.220.75" "curl/7.54.0" "28255618-6ca5-9d91-9634-c562694a3625" "httpbin.org" "34.232.181.106:80" outbound|80||httpbin.org - 172.30.230.33:80 10.127.220.75:52077 -

Access the edition.cnn.com service through your ingress gateway:

$ curl -s --resolve edition.cnn.com:$SECURE_INGRESS_PORT:$INGRESS_HOST https://edition.cnn.com:$SECURE_INGRESS_PORT | grep -o "<title>.*</title>"
<title>CNN International - Breaking News, US News, World News and Video</title>

If the Istio ingress gateway is deployed in the istio-system namespace, print the gateway’s log with the following command:
```
$ kubectl logs -l istio=ingressgateway -c istio-proxy -n istio-system | grep 'edition.cnn.com'
```

Search the log for an entry similar to:

[2019-01-31T13:40:11.076Z] "- - -" 0 - 589 17798 1644 - "-" "-" "-" "-" "172.217.31.132:443" outbound|443||edition.cnn.com 172.30.230.33:54508 172.30.230.33:443 10.127.220.75:49467 edition.cnn.com

Cleanup

Remove the gateway, the virtual services and the service entries:

$ kubectl delete gateway proxy
$ kubectl delete virtualservice cnn httpbin
$ kubectl delete serviceentry cnn httpbin-ext localhost
$ kubectl delete destinationrule localhost