Egress Gateways

The Control Egress Traffic task shows how to configure Istio to allow access to external HTTP and HTTPS services from applications inside the mesh. There, the external services are called directly from the client sidecar. This example also shows how to configure Istio to call external services, although this time indirectly via a dedicated egress gateway service.

Istio uses ingress and egress gateways to configure load balancers executing at the edge of a service mesh. An ingress gateway allows you to define entry points into the mesh that all incoming traffic flows through. Egress gateway is a symmetrical concept; it defines exit points from the mesh. Egress gateways allow you to apply Istio features, for example, monitoring and route rules, to traffic exiting the mesh.

Use case

Consider an organization that has a strict security requirement that all traffic leaving the service mesh must flow through a set of dedicated nodes. These nodes will run on dedicated machines, separated from the rest of the nodes running applications in the cluster. These special nodes will serve for policy enforcement on the egress traffic and will be monitored more thoroughly than other nodes.

Another use case is a cluster where the application nodes don’t have public IPs, so the in-mesh services that run on them cannot access the Internet. Defining an egress gateway, directing all the egress traffic through it, and allocating public IPs to the egress gateway nodes allows the application nodes to access external services in a controlled way.

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})
    

Deploy Istio egress gateway

  1. Check if the Istio egress gateway is deployed:

    $ kubectl get pod -l istio=egressgateway -n istio-system
    

    If no pods are returned, deploy the Istio egress gateway by performing the next step.

  2. Use helm template (or helm install with the corresponding flags):

    $ helm template install/kubernetes/helm/istio --name istio-egressgateway --namespace istio-system \
        -x charts/gateways/templates/deployment.yaml -x charts/gateways/templates/service.yaml \
        -x charts/gateways/templates/serviceaccount.yaml -x charts/gateways/templates/autoscale.yaml \
        -x charts/gateways/templates/clusterrole.yaml -x charts/gateways/templates/clusterrolebindings.yaml \
        --set global.istioNamespace=istio-system --set gateways.istio-ingressgateway.enabled=false \
        --set gateways.istio-egressgateway.enabled=true | kubectl apply -f -
    

Egress gateway for HTTP traffic

First create a ServiceEntry to allow direct traffic to an external service.

  1. Define a ServiceEntry for edition.cnn.com:

    $ kubectl apply -f - <<EOF
    apiVersion: networking.istio.io/v1alpha3
    kind: ServiceEntry
    metadata:
      name: cnn
    spec:
      hosts:
      - edition.cnn.com
      ports:
      - number: 80
        name: http-port
        protocol: HTTP
      - number: 443
        name: https
        protocol: HTTPS
      resolution: DNS
    EOF
    
  2. Verify that your ServiceEntry was applied correctly by sending an HTTP request to http://edition.cnn.com/politics.

    $ kubectl exec -it $SOURCE_POD -c sleep -- curl -sL -o /dev/null -D - http://edition.cnn.com/politics
    HTTP/1.1 301 Moved Permanently
    ...
    location: https://edition.cnn.com/politics
    ...
    
    HTTP/1.1 200 OK
    Content-Type: text/html; charset=utf-8
    ...
    Content-Length: 151654
    ...
    

    The output should be the same as in the TLS Origination for Egress Traffic example, without TLS origination.

  3. Create an egress Gateway for edition.cnn.com, port 80, and a destination rule for traffic directed to the egress gateway.

    Choose the instructions corresponding to whether or not you have mutual TLS Authentication enabled in Istio.

    $ kubectl apply -f - <<EOF
    apiVersion: networking.istio.io/v1alpha3
    kind: Gateway
    metadata:
      name: istio-egressgateway
    spec:
      selector:
        istio: egressgateway
      servers:
      - port:
          number: 80
          name: https
          protocol: HTTPS
        hosts:
        - edition.cnn.com
        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-cnn
    spec:
      host: istio-egressgateway.istio-system.svc.cluster.local
      subsets:
      - name: cnn
        trafficPolicy:
          loadBalancer:
            simple: ROUND_ROBIN
          portLevelSettings:
          - port:
              number: 80
            tls:
              mode: ISTIO_MUTUAL
              sni: edition.cnn.com
    EOF
    
  4. Define a VirtualService to direct traffic from the sidecars to the egress gateway and from the egress gateway to the external service:

    $ kubectl apply -f - <<EOF
    apiVersion: networking.istio.io/v1alpha3
    kind: VirtualService
    metadata:
      name: direct-cnn-through-egress-gateway
    spec:
      hosts:
      - edition.cnn.com
      gateways:
      - istio-egressgateway
      - mesh
      http:
      - match:
        - gateways:
          - mesh
          port: 80
        route:
        - destination:
            host: istio-egressgateway.istio-system.svc.cluster.local
            subset: cnn
            port:
              number: 80
          weight: 100
      - match:
        - gateways:
          - istio-egressgateway
          port: 80
        route:
        - destination:
            host: edition.cnn.com
            port:
              number: 80
          weight: 100
    EOF
    
  5. Resend the HTTP request to http://edition.cnn.com/politics.

    $ kubectl exec -it $SOURCE_POD -c sleep -- curl -sL -o /dev/null -D - http://edition.cnn.com/politics
    HTTP/1.1 301 Moved Permanently
    ...
    location: https://edition.cnn.com/politics
    ...
    
    HTTP/1.1 200 OK
    Content-Type: text/html; charset=utf-8
    ...
    Content-Length: 151654
    ...
    

    The output should be the same as in the step 2.

  6. Check the log of the istio-egressgateway pod for a line corresponding to our request. If Istio is deployed in the istio-system namespace, the command to print the log is:

    $ kubectl logs -l istio=egressgateway -c istio-proxy -n istio-system | tail
    

    You should see a line similar to the following:

    [2018-06-14T11:46:23.596Z] "GET /politics HTTP/2" 301 - 0 0 3 1 "172.30.146.87" "curl/7.35.0" "ab7be694-e367-94c5-83d1-086eca996dae" "edition.cnn.com" "151.101.193.67:80"
    

    Note that you only redirected the traffic from port 80 to the egress gateway. The HTTPS traffic to port 443 went directly to edition.cnn.com.

Cleanup HTTP gateway

Remove the previous definitions before proceeding to the next step:

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

Egress gateway for HTTPS traffic

In this section you direct HTTPS traffic (TLS originated by the application) through an egress gateway. You need to specify port 443 with protocol TLS in a corresponding ServiceEntry, an egress Gateway and a VirtualService.

  1. Define a ServiceEntry for edition.cnn.com:

    $ kubectl apply -f - <<EOF
    apiVersion: networking.istio.io/v1alpha3
    kind: ServiceEntry
    metadata:
      name: cnn
    spec:
      hosts:
      - edition.cnn.com
      ports:
      - number: 443
        name: tls
        protocol: TLS
      resolution: DNS
    EOF
    
  2. Verify that your ServiceEntry was applied correctly by sending an HTTPS request to http://edition.cnn.com/politics.

    $ kubectl exec -it $SOURCE_POD -c sleep -- curl -sL -o /dev/null -D - https://edition.cnn.com/politics
    HTTP/1.1 200 OK
    Content-Type: text/html; charset=utf-8
    ...
    Content-Length: 151654
    ...
    
  3. Create an egress Gateway for edition.cnn.com, a destination rule and a virtual service to direct the traffic through the egress gateway and from the egress gateway to the external service.

    Choose the instructions corresponding to whether or not you have mutual TLS Authentication enabled in Istio.

    $ 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-cnn
          protocol: TLS
        hosts:
        - edition.cnn.com
        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-cnn
    spec:
      host: istio-egressgateway.istio-system.svc.cluster.local
      subsets:
      - name: cnn
        trafficPolicy:
          loadBalancer:
            simple: ROUND_ROBIN
          portLevelSettings:
          - port:
              number: 443
            tls:
              mode: ISTIO_MUTUAL
              sni: edition.cnn.com
    ---
    apiVersion: networking.istio.io/v1alpha3
    kind: VirtualService
    metadata:
      name: direct-cnn-through-egress-gateway
    spec:
      hosts:
      - edition.cnn.com
      gateways:
      - mesh
      - istio-egressgateway
      tls:
      - match:
        - gateways:
          - mesh
          port: 443
          sni_hosts:
          - edition.cnn.com
        route:
        - destination:
            host: istio-egressgateway.istio-system.svc.cluster.local
            subset: cnn
            port:
              number: 443
      tcp:
      - match:
        - gateways:
          - istio-egressgateway
          port: 443
        route:
        - destination:
            host: edition.cnn.com
            port:
              number: 443
          weight: 100
    EOF
    
  4. Send an HTTPS request to http://edition.cnn.com/politics. The output should be the same as before.

    $ kubectl exec -it $SOURCE_POD -c sleep -- curl -sL -o /dev/null -D - https://edition.cnn.com/politics
    HTTP/1.1 200 OK
    Content-Type: text/html; charset=utf-8
    ...
    Content-Length: 151654
    ...
    
  5. Check the log of the egress gateway’s proxy. If Istio is deployed in the istio-system namespace, the command to print the log is:

    $ kubectl logs -l istio=egressgateway -n istio-system
    

    You should see a line similar to the following:

    [2019-01-02T11:46:46.981Z] "- - -" 0 - 627 1879689 44 - "-" "-" "-" "-" "151.101.129.67:443" outbound|443||edition.cnn.com 172.30.109.80:41122 172.30.109.80:443 172.30.109.112:59970 edition.cnn.com
    

Cleanup HTTPS gateway

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

Additional security considerations

Note that defining an egress Gateway in Istio does not in itself provides any special treatment for the nodes on which the egress gateway service runs. It is up to the cluster administrator or the cloud provider to deploy the egress gateways on dedicated nodes and to introduce additional security measures to make these nodes more secure than the rest of the mesh.

Istio cannot securely enforce that all egress traffic actually flows through the egress gateways. Istio only enables such flow through its sidecar proxies. If attackers bypass the sidecar proxy, they could directly access external services without traversing the egress gateway. Thus, the attackers escape Istio’s control and monitoring. The cluster administrator or the cloud provider must ensure that no traffic leaves the mesh bypassing the egress gateway. Mechanisms external to Istio must enforce this requirement. For example, the cluster administrator can configure a firewall to deny all traffic not coming from the egress gateway. The Kubernetes network policies can also forbid all the egress traffic not originating from the egress gateway (see the next section for an example). Additionally, the cluster administrator or the cloud provider can configure the network to ensure application nodes can only access the Internet via a gateway. To do this, the cluster administrator or the cloud provider can prevent the allocation of public IPs to pods other than gateways and can configure NAT devices to drop packets not originating at the egress gateways.

Apply Kubernetes network policies

This section shows you how to create a Kubernetes network policy to prevent bypassing of the egress gateway. To test the network policy, you create a namespace, test-egress, deploy the sleep sample to it, and then attempt to send requests to a gateway-secured external service.

  1. Follow the steps in the Egress gateway for HTTPS traffic section.

  2. Create the test-egress namespace:

    $ kubectl create namespace test-egress
    
  3. Deploy the sleep sample to the test-egress namespace.

    Zip
    $ kubectl apply -n test-egress -f @samples/sleep/sleep.yaml@
    
  4. Check that the deployed pod has a single container with no Istio sidecar attached:

    $ kubectl get pod $(kubectl get pod -n test-egress -l app=sleep -o jsonpath={.items..metadata.name}) -n test-egress
    NAME                     READY     STATUS    RESTARTS   AGE
    sleep-776b7bcdcd-z7mc4   1/1       Running   0          18m
    
  5. Send an HTTPS request to https://edition.cnn.com/politics from the sleep pod in the test-egress namespace. The request will succeed since you did not define any restrictive policies yet.

    $ kubectl exec -it $(kubectl get pod -n test-egress -l app=sleep -o jsonpath={.items..metadata.name}) -n test-egress -c sleep -- curl -s -o /dev/null -w "%{http_code}\n"  https://edition.cnn.com/politics
    200
    
  6. Label the namespaces where the Istio components (the control plane and the gateways) run. If you deployed the Istio components to istio-system, the command is:

    $ kubectl label namespace istio-system istio=system
    
  7. Label the kube-system namespace.

    $ kubectl label ns kube-system kube-system=true
    
  8. Define a NetworkPolicy to limit the egress traffic from the test-egress namespace to traffic destined to istio-system, and to the kube-system DNS service (port 53):

    $ cat <<EOF | kubectl apply -n test-egress -f -
    apiVersion: networking.k8s.io/v1
    kind: NetworkPolicy
    metadata:
      name: allow-egress-to-istio-system-and-kube-dns
    spec:
      podSelector: {}
      policyTypes:
      - Egress
      egress:
      - to:
        - namespaceSelector:
            matchLabels:
              kube-system: "true"
        ports:
        - protocol: UDP
          port: 53
      - to:
        - namespaceSelector:
            matchLabels:
              istio: system
    EOF
    
  9. Resend the previous HTTPS request to https://edition.cnn.com/politics. Now it should fail since the traffic is blocked by the network policy. Note that the sleep pod cannot bypass istio-egressgateway. The only way it can access edition.cnn.com is by using an Istio sidecar proxy and by directing the traffic to istio-egressgateway. This setting demonstrates that even if some malicious pod manages to bypass its sidecar proxy, it will not be able to access external sites and will be blocked by the network policy.

    $ kubectl exec -it $(kubectl get pod -n test-egress -l app=sleep -o jsonpath={.items..metadata.name}) -n test-egress -c sleep -- curl -v https://edition.cnn.com/politics
    Hostname was NOT found in DNS cache
      Trying 151.101.65.67...
      Trying 2a04:4e42:200::323...
    Immediate connect fail for 2a04:4e42:200::323: Cannot assign requested address
      Trying 2a04:4e42:400::323...
    Immediate connect fail for 2a04:4e42:400::323: Cannot assign requested address
      Trying 2a04:4e42:600::323...
    Immediate connect fail for 2a04:4e42:600::323: Cannot assign requested address
      Trying 2a04:4e42::323...
    Immediate connect fail for 2a04:4e42::323: Cannot assign requested address
    connect to 151.101.65.67 port 443 failed: Connection timed out
    
  10. Now inject an Istio sidecar proxy into the sleep pod in the test-egress namespace by first enabling automatic sidecar proxy injection in the test-egress namespace:

    $ kubectl label namespace test-egress istio-injection=enabled
    
  11. Then redeploy the sleep deployment:

    Zip
    $ kubectl delete deployment sleep -n test-egress
    $ kubectl apply -f @samples/sleep/sleep.yaml@ -n test-egress
    
  12. Check that the deployed pod has two containers, including the Istio sidecar proxy (istio-proxy):

    $ kubectl get pod $(kubectl get pod -n test-egress -l app=sleep -o jsonpath={.items..metadata.name}) -n test-egress -o jsonpath={.spec.containers[*].name}
    sleep istio-proxy
    
  13. Send an HTTPS request to https://edition.cnn.com/politics. Now it should succeed since the traffic flows to istio-egressgateway in the istio-system namespace, which is allowed by the Network Policy you defined. istio-egressgateway forwards the traffic to edition.cnn.com.

    $ kubectl exec -it $(kubectl get pod -n test-egress -l app=sleep -o jsonpath={.items..metadata.name}) -n test-egress -c sleep -- curl -s -o /dev/null -w "%{http_code}\n" https://edition.cnn.com/politics
    200
    
  14. Check the statistics of the egress gateway’s proxy and see a counter that corresponds to our requests to edition.cnn.com. 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 -- curl -s localhost:15000/stats | grep edition.cnn.com.upstream_cx_total
    cluster.outbound|443||edition.cnn.com.upstream_cx_total: 2
    

Cleanup network policies

  1. Delete the resources created in this section:

    Zip
    $ kubectl delete -f @samples/sleep/sleep.yaml@ -n test-egress
    $ kubectl delete networkpolicy allow-egress-to-istio-system-and-kube-dns -n test-egress
    $ kubectl label namespace kube-system kube-system-
    $ kubectl label namespace istio-system istio-
    $ kubectl delete namespace test-egress
    
  2. Follow the steps in the Cleanup HTTPS gateway section.

Troubleshooting

  1. Check if you have mutual TLS Authentication enabled in Istio, following the steps in Verify mutual TLS configuration. If mutual TLS is enabled, make sure you create the configuration items accordingly (note the remarks If you have mutual TLS Authentication enabled in Istio, you must create…).

  2. If mutual TLS Authentication is enabled, verify the correct certificate of the egress gateway:

    $ kubectl exec -i -n istio-system $(kubectl get pod -l istio=egressgateway -n istio-system -o jsonpath='{.items[0].metadata.name}')  -- cat /etc/certs/cert-chain.pem | openssl x509 -text -noout  | grep 'Subject Alternative Name' -A 1
            X509v3 Subject Alternative Name:
                URI:spiffe://cluster.local/ns/istio-system/sa/istio-egressgateway-service-account
    
  3. For HTTPS traffic (TLS originated by the application), test the traffic flow by using the openssl command. openssl has an explicit option for setting the SNI, namely -servername.

    $ kubectl exec -it $SOURCE_POD -c sleep -- openssl s_client -connect edition.cnn.com:443 -servername edition.cnn.com
    CONNECTED(00000003)
    ...
    Certificate chain
     0 s:/C=US/ST=California/L=San Francisco/O=Fastly, Inc./CN=turner-tls.map.fastly.net
       i:/C=BE/O=GlobalSign nv-sa/CN=GlobalSign CloudSSL CA - SHA256 - G3
     1 s:/C=BE/O=GlobalSign nv-sa/CN=GlobalSign CloudSSL CA - SHA256 - G3
       i:/C=BE/O=GlobalSign nv-sa/OU=Root CA/CN=GlobalSign Root CA
     ---
     Server certificate
     -----BEGIN CERTIFICATE-----
    ...
    

    If you get the certificate as in the output above, your traffic is routed correctly. Check the statistics of the egress gateway’s proxy and see a counter that corresponds to your requests (sent by openssl and curl) to edition.cnn.com.

    $ kubectl exec -it $(kubectl get pod -l istio=egressgateway -n istio-system -o jsonpath='{.items[0].metadata.name}') -c istio-proxy -n istio-system -- curl -s localhost:15000/stats | grep edition.cnn.com.upstream_cx_total
    cluster.outbound|443||edition.cnn.com.upstream_cx_total: 2
    

Cleanup

Shutdown the sleep service:

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