Egress using Wildcard Hosts

 12 minute read

The Control Egress Traffic 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

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

  • Deploy the sleep 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/sleep/sleep.yaml@

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

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

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

    $ export SOURCE_POD=$(kubectl get pod -l app=sleep -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 and corresponding VirtualSevice for *.wikipedia.org:

    $ kubectl apply -f - <<EOF
apiVersion: networking.istio.io/v1alpha3
kind: ServiceEntry
metadata:
  name: wikipedia
spec:
  hosts:
  - "*.wikipedia.org"
  ports:
  - number: 443
    name: tls
    protocol: TLS
---
apiVersion: networking.istio.io/v1alpha3
kind: VirtualService
metadata:
  name: wikipedia
spec:
  hosts:
  - "*.wikipedia.org"
  tls:
  - match:
    - port: 443
      sni_hosts:
      - "*.wikipedia.org"
    route:
    - destination:
        host: "*.wikipedia.org"
        port:
          number: 443
EOF

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

    $ kubectl exec -it $SOURCE_POD -c sleep -- 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
$ kubectl delete virtualservice wikipedia

Configure egress gateway traffic to a wildcard host

The configuration for accessing a wildcard host via an egress gateway depends on whether or not the set of wildcard domains are served by a single common host. This is the case for *.wikipedia.org. All of the language-specific sites are served by every one of the wikipedia.org servers. You can route the traffic to an IP of any *.wikipedia.org site, including www.wikipedia.org, and it will manage to serve any specific site.

In the general case, where all the domain names of a wildcard are not served by a single hosting server, a more complex configuration is required.

Wildcard configuration for a single hosting server

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, a destination rule and a virtual service 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/v1alpha3
kind: Gateway
metadata:
  name: istio-egressgateway
spec:
  selector:
    istio: egressgateway
  servers:
  - port:
      number: 443
      name: tls
      protocol: TLS
    hosts:
    - "*.wikipedia.org"
    tls:
      mode: PASSTHROUGH
---
apiVersion: networking.istio.io/v1alpha3
kind: DestinationRule
metadata:
  name: egressgateway-for-wikipedia
spec:
  host: istio-egressgateway.istio-system.svc.cluster.local
  subsets:
    - name: wikipedia
---
apiVersion: networking.istio.io/v1alpha3
kind: VirtualService
metadata:
  name: direct-wikipedia-through-egress-gateway
spec:
  hosts:
  - "*.wikipedia.org"
  gateways:
  - mesh
  - istio-egressgateway
  tls:
  - match:
    - gateways:
      - mesh
      port: 443
      sni_hosts:
      - "*.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
      sni_hosts:
      - "*.wikipedia.org"
    route:
    - destination:
        host: www.wikipedia.org
        port:
          number: 443
      weight: 100
EOF

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

    $ kubectl apply -f - <<EOF
apiVersion: networking.istio.io/v1alpha3
kind: ServiceEntry
metadata:
  name: www-wikipedia
spec:
  hosts:
  - www.wikipedia.org
  ports:
  - number: 443
    name: tls
    protocol: TLS
  resolution: DNS
EOF

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

    $ kubectl exec -it $SOURCE_POD -c sleep -- 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>

  4. Check the statistics of the egress gateway’s proxy for the counter that corresponds to your requests to *.wikipedia.org. If Istio is deployed in the istio-system namespace, the command to print the counter is:

    $ kubectl exec -it $(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 wildcard configuration for a single hosting server

$ 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. In the previous section you directed the traffic to www.wikipedia.org, which was made known to your gateway during configuration. The gateway, however, would not know the IP address of any arbitrary host it receives in a request. This is due to a limitation of Envoy, the proxy used by the default Istio egress gateway. Envoy routes traffic either to predefined hosts, predefined IP addresses, or to the original destination IP address of the request. In the gateway case, the original destination IP of the request is lost since the request is first routed to the egress gateway and its destination IP address is the IP address of the gateway.

Consequently, the Istio gateway based on Envoy cannot route traffic to an arbitrary host that is not preconfigured, and therefore is unable to perform traffic control for arbitrary wildcard domains. To enable such traffic control for HTTPS, and for any TLS, you need to deploy an SNI forward proxy in addition to Envoy. Envoy will route the requests destined for a wildcard domain to the SNI forward proxy, which, in turn, will forward the requests to the destination specified by the SNI value.

The egress gateway with SNI proxy and the related parts of the Istio architecture are shown in the following diagram:

Egress Gateway with SNI proxy
Egress Gateway with SNI proxy

The following sections show you how to redeploy the egress gateway with an SNI proxy and then configure Istio to route HTTPS traffic through the gateway to arbitrary wildcard domains.

Setup egress gateway with SNI proxy

In this section you deploy an egress gateway with an SNI proxy in addition to the standard Istio Envoy proxy. This example uses Nginx for the SNI proxy, although any SNI proxy that is capable of routing traffic according to arbitrary, not-preconfigured, SNI values would do. The SNI proxy will listen on port 8443, although you can use any port other than the ports specified for the egress Gateway and for the VirtualServices bound to it. The SNI proxy will forward the traffic to port 443.

  1. Create a configuration file for the Nginx SNI proxy. You may want to edit the file to specify additional Nginx settings, if required. Note that the listen directive of the server specifies port 8443, its proxy_pass directive uses ssl_preread_server_name with port 443 and ssl_preread is on to enable SNI reading.

    $ cat <<EOF > ./sni-proxy.conf
user www-data;

events {
}

stream {
  log_format log_stream '\$remote_addr [\$time_local] \$protocol [\$ssl_preread_server_name]'
  '\$status \$bytes_sent \$bytes_received \$session_time';

  access_log /var/log/nginx/access.log log_stream;
  error_log  /var/log/nginx/error.log;

  # tcp forward proxy by SNI
  server {
    resolver 8.8.8.8 ipv6=off;
    listen       127.0.0.1:8443;
    proxy_pass   \$ssl_preread_server_name:443;
    ssl_preread  on;
  }
}
EOF

  2. Create a Kubernetes ConfigMap to hold the configuration of the Nginx SNI proxy:

    $ kubectl create configmap egress-sni-proxy-configmap -n istio-system --from-file=nginx.conf=./sni-proxy.conf

  3. The following command will generate istio-egressgateway-with-sni-proxy.yaml which you can optionally edit and then deploy.

    $ cat <<EOF | istioctl manifest generate --set values.global.istioNamespace=istio-system -f - > ./istio-egressgateway-with-sni-proxy.yaml
gateways:
  enabled: true
  istio-ingressgateway:
    enabled: false
  istio-egressgateway:
    enabled: false
  istio-egressgateway-with-sni-proxy:
    enabled: true
    labels:
      app: istio-egressgateway-with-sni-proxy
      istio: egressgateway-with-sni-proxy
    replicaCount: 1
    autoscaleMin: 1
    autoscaleMax: 5
    cpu:
      targetAverageUtilization: 80
    serviceAnnotations: {}
    type: ClusterIP
    ports:
      - port: 443
        name: https
    secretVolumes:
      - name: egressgateway-certs
        secretName: istio-egressgateway-certs
        mountPath: /etc/istio/egressgateway-certs
      - name: egressgateway-ca-certs
        secretName: istio-egressgateway-ca-certs
        mountPath: /etc/istio/egressgateway-ca-certs
    configVolumes:
      - name: sni-proxy-config
        configMapName: egress-sni-proxy-configmap
    additionalContainers:
    - name: sni-proxy
      image: nginx
      volumeMounts:
      - name: sni-proxy-config
        mountPath: /etc/nginx
        readOnly: true
EOF

  4. Deploy the new egress gateway:

    $ kubectl apply -f ./istio-egressgateway-with-sni-proxy.yaml
serviceaccount "istio-egressgateway-with-sni-proxy-service-account" created
role "istio-egressgateway-with-sni-proxy-istio-system" created
rolebinding "istio-egressgateway-with-sni-proxy-istio-system" created
service "istio-egressgateway-with-sni-proxy" created
deployment "istio-egressgateway-with-sni-proxy" created
horizontalpodautoscaler "istio-egressgateway-with-sni-proxy" created

  5. Verify that the new egress gateway is running. Note that the pod has two containers (one is the Envoy proxy and the second one is the SNI proxy).

    $ kubectl get pod -l istio=egressgateway-with-sni-proxy -n istio-system
NAME                                                  READY     STATUS    RESTARTS   AGE
istio-egressgateway-with-sni-proxy-79f6744569-pf9t2   2/2       Running   0          17s

  6. Create a service entry with a static address equal to 127.0.0.1 (localhost), and disable mutual TLS for traffic directed to the new service entry:

    $ kubectl apply -f - <<EOF
apiVersion: networking.istio.io/v1alpha3
kind: ServiceEntry
metadata:
  name: sni-proxy
spec:
  hosts:
  - sni-proxy.local
  location: MESH_EXTERNAL
  ports:
  - number: 8443
    name: tcp
    protocol: TCP
  resolution: STATIC
  endpoints:
  - address: 127.0.0.1
---
apiVersion: networking.istio.io/v1alpha3
kind: DestinationRule
metadata:
  name: disable-mtls-for-sni-proxy
spec:
  host: sni-proxy.local
  trafficPolicy:
    tls:
      mode: DISABLE
EOF

Configure traffic through egress gateway with SNI proxy

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

    $ cat <<EOF | kubectl create -f -
apiVersion: networking.istio.io/v1alpha3
kind: ServiceEntry
metadata:
  name: wikipedia
spec:
  hosts:
  - "*.wikipedia.org"
  ports:
  - number: 443
    name: tls
    protocol: TLS
EOF

  2. Create an egress Gateway for *.wikipedia.org, port 443, protocol TLS, and a virtual service to direct the traffic destined for *.wikipedia.org through the gateway.

    Choose the instructions corresponding to whether or not you want to enable mutual TLS Authentication between the source pod and the egress gateway.

    $ kubectl apply -f - <<EOF
apiVersion: networking.istio.io/v1alpha3
kind: Gateway
metadata:
  name: istio-egressgateway-with-sni-proxy
spec:
  selector:
istio: egressgateway-with-sni-proxy
  servers:
  - port:
  number: 443
  name: tls-egress
  protocol: TLS
hosts:
- "*.wikipedia.org"
tls:
  mode: MUTUAL
  serverCertificate: /etc/certs/cert-chain.pem
  privateKey: /etc/certs/key.pem
  caCertificates: /etc/certs/root-cert.pem
---
apiVersion: networking.istio.io/v1alpha3
kind: DestinationRule
metadata:
  name: egressgateway-for-wikipedia
spec:
  host: istio-egressgateway-with-sni-proxy.istio-system.svc.cluster.local
  subsets:
- name: wikipedia
  trafficPolicy:
    loadBalancer:
      simple: ROUND_ROBIN
    portLevelSettings:
    - port:
        number: 443
      tls:
        mode: ISTIO_MUTUAL
---
apiVersion: networking.istio.io/v1alpha3
kind: VirtualService
metadata:
  name: direct-wikipedia-through-egress-gateway
spec:
  hosts:
  - "*.wikipedia.org"
  gateways:
  - mesh
  - istio-egressgateway-with-sni-proxy
  tls:
  - match:
- gateways:
  - mesh
  port: 443
  sni_hosts:
  - "*.wikipedia.org"
route:
- destination:
    host: istio-egressgateway-with-sni-proxy.istio-system.svc.cluster.local
    subset: wikipedia
    port:
      number: 443
  weight: 100
  tcp:
  - match:
- gateways:
  - istio-egressgateway-with-sni-proxy
  port: 443
route:
- destination:
    host: sni-proxy.local
    port:
      number: 8443
  weight: 100
---
# The following filter is used to forward the original SNI (sent by the application) as the SNI of the mutual TLS
# connection.
# The forwarded SNI will be reported to Mixer so that policies will be enforced based on the original SNI value.
apiVersion: networking.istio.io/v1alpha3
kind: EnvoyFilter
metadata:
  name: forward-downstream-sni
spec:
  filters:
  - listenerMatch:
  portNumber: 443
  listenerType: SIDECAR_OUTBOUND
filterName: forward_downstream_sni
filterType: NETWORK
filterConfig: {}
---
# The following filter verifies that the SNI of the mutual TLS connection (the SNI reported to Mixer) is
# identical to the original SNI issued by the application (the SNI used for routing by the SNI proxy).
# The filter prevents Mixer from being deceived by a malicious application: routing to one SNI while
# reporting some other value of SNI. If the original SNI does not match the SNI of the mutual TLS connection, the
# filter will block the connection to the external service.
apiVersion: networking.istio.io/v1alpha3
kind: EnvoyFilter
metadata:
  name: egress-gateway-sni-verifier
spec:
  workloadLabels:
app: istio-egressgateway-with-sni-proxy
  filters:
  - listenerMatch:
  portNumber: 443
  listenerType: GATEWAY
filterName: sni_verifier
filterType: NETWORK
filterConfig: {}
EOF

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

    $ kubectl exec -it $SOURCE_POD -c sleep -- 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>

  4. Check the log of the egress gateway’s Envoy proxy. If Istio is deployed in the istio-system namespace, the command to print the log is:

    $ kubectl logs -l istio=egressgateway-with-sni-proxy -c istio-proxy -n istio-system

    You should see lines similar to the following:

    [2019-01-02T16:34:23.312Z] "- - -" 0 - 578 79141 624 - "-" "-" "-" "-" "127.0.0.1:8443" outbound|8443||sni-proxy.local 127.0.0.1:55018 172.30.109.84:443 172.30.109.112:45346 en.wikipedia.org
[2019-01-02T16:34:24.079Z] "- - -" 0 - 586 65770 638 - "-" "-" "-" "-" "127.0.0.1:8443" outbound|8443||sni-proxy.local 127.0.0.1:55034 172.30.109.84:443 172.30.109.112:45362 de.wikipedia.org

  5. Check the logs of the SNI proxy. If Istio is deployed in the istio-system namespace, the command to print the log is:

    $ kubectl logs -l istio=egressgateway-with-sni-proxy -n istio-system -c sni-proxy
127.0.0.1 [01/Aug/2018:15:32:02 +0000] TCP [en.wikipedia.org]200 81513 280 0.600
127.0.0.1 [01/Aug/2018:15:32:03 +0000] TCP [de.wikipedia.org]200 67745 291 0.659

  6. Check the mixer log. If Istio is deployed in the istio-system namespace, the command to print the log is:

    $ kubectl -n istio-system logs -l istio-mixer-type=telemetry -c mixer | grep '"connectionEvent":"open"' | grep '"sourceName":"istio-egressgateway' | grep 'wikipedia.org'
{"level":"info","time":"2018-08-26T16:16:34.784571Z","instance":"tcpaccesslog.logentry.istio-system","connectionDuration":"0s","connectionEvent":"open","connection_security_policy":"unknown","destinationApp":"","destinationIp":"127.0.0.1","destinationName":"unknown","destinationNamespace":"default","destinationOwner":"unknown","destinationPrincipal":"cluster.local/ns/istio-system/sa/istio-egressgateway-with-sni-proxy-service-account","destinationServiceHost":"","destinationWorkload":"unknown","protocol":"tcp","receivedBytes":298,"reporter":"source","requestedServerName":"en.wikipedia.org","sentBytes":0,"sourceApp":"istio-egressgateway-with-sni-proxy","sourceIp":"172.30.146.88","sourceName":"istio-egressgateway-with-sni-proxy-7c4f7868fb-rc8pr","sourceNamespace":"istio-system","sourceOwner":"kubernetes://apis/extensions/v1beta1/namespaces/istio-system/deployments/istio-egressgateway-with-sni-proxy","sourcePrincipal":"cluster.local/ns/sleep/sa/default","sourceWorkload":"istio-egressgateway-with-sni-proxy","totalReceivedBytes":298,"totalSentBytes":0}

    Note the requestedServerName attribute.

Cleanup wildcard configuration for arbitrary domains

  1. Delete the configuration items for *.wikipedia.org:

    $ kubectl delete serviceentry wikipedia
$ kubectl delete gateway istio-egressgateway-with-sni-proxy
$ kubectl delete virtualservice direct-wikipedia-through-egress-gateway
$ kubectl delete destinationrule egressgateway-for-wikipedia
$ kubectl delete --ignore-not-found=true envoyfilter forward-downstream-sni egress-gateway-sni-verifier

  2. Delete the configuration items for the egressgateway-with-sni-proxy deployment:

    $ kubectl delete serviceentry sni-proxy
$ kubectl delete destinationrule disable-mtls-for-sni-proxy
$ kubectl delete -f ./istio-egressgateway-with-sni-proxy.yaml
$ kubectl delete configmap egress-sni-proxy-configmap -n istio-system

  3. Remove the configuration files you created:

    $ rm ./istio-egressgateway-with-sni-proxy.yaml
$ rm ./sni-proxy.conf

Cleanup

Shutdown the sleep service:

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