Egress Gateways

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The Accessing External Services 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 curl sample app to use as a test source for sending requests.

    Zip
    $ kubectl apply -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})

  • Enable Envoy’s access logging if not already enabled. For example, using istioctl:

    $ istioctl install <flags-you-used-to-install-Istio> --set meshConfig.accessLogFile=/dev/stdout

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 following step.

  2. If you used an IstioOperator CR to install Istio, add the following fields to your configuration:

    spec:
  components:
    egressGateways:
    - name: istio-egressgateway
      enabled: true

    Otherwise, add the equivalent settings to your original istioctl install command, for example:

    $ istioctl install <flags-you-used-to-install-Istio> \
                   --set "components.egressGateways[0].name=istio-egressgateway" \
                   --set "components.egressGateways[0].enabled=true"

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/v1
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 "$SOURCE_POD" -c curl -- curl -sSL -o /dev/null -D - http://edition.cnn.com/politics
...
HTTP/1.1 301 Moved Permanently
...
location: https://edition.cnn.com/politics
...

HTTP/2 200
Content-Type: text/html; charset=utf-8
...

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

  3. Create a Gateway for egress traffic to edition.cnn.com port 80.

$ kubectl apply -f - <<EOF
apiVersion: networking.istio.io/v1
kind: Gateway
metadata:
  name: istio-egressgateway
spec:
  selector:
    istio: egressgateway
  servers:
  - port:
      number: 80
      name: http
      protocol: HTTP
    hosts:
    - edition.cnn.com
---
apiVersion: networking.istio.io/v1
kind: DestinationRule
metadata:
  name: egressgateway-for-cnn
spec:
  host: istio-egressgateway.istio-system.svc.cluster.local
  subsets:
  - name: cnn
EOF
  1. Configure route rules 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/v1
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

  1. Resend the HTTP request to http://edition.cnn.com/politics.

    $ kubectl exec "$SOURCE_POD" -c curl -- curl -sSL -o /dev/null -D - http://edition.cnn.com/politics
...
HTTP/1.1 301 Moved Permanently
...
location: https://edition.cnn.com/politics
...

HTTP/2 200
Content-Type: text/html; charset=utf-8
...

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

  2. Check the log of the egress gateway 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:

[2019-09-03T20:57:49.103Z] "GET /politics HTTP/2" 301 - "-" "-" 0 0 90 89 "10.244.2.10" "curl/7.64.0" "ea379962-9b5c-4431-ab66-f01994f5a5a5" "edition.cnn.com" "151.101.65.67:80" outbound|80||edition.cnn.com - 10.244.1.5:80 10.244.2.10:50482 edition.cnn.com -

Note that you only redirected the HTTP traffic from port 80 through 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 serviceentry cnn
$ kubectl delete gateway istio-egressgateway
$ 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 and egress Gateway.

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

    $ kubectl apply -f - <<EOF
apiVersion: networking.istio.io/v1
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 https://edition.cnn.com/politics.

    $ kubectl exec "$SOURCE_POD" -c curl -- curl -sSL -o /dev/null -D - https://edition.cnn.com/politics
...
HTTP/2 200
Content-Type: text/html; charset=utf-8
...

  3. Create an egress Gateway for edition.cnn.com 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: tls
      protocol: TLS
    hosts:
    - edition.cnn.com
    tls:
      mode: PASSTHROUGH
---
apiVersion: networking.istio.io/v1
kind: DestinationRule
metadata:
  name: egressgateway-for-cnn
spec:
  host: istio-egressgateway.istio-system.svc.cluster.local
  subsets:
  - name: cnn
---
apiVersion: networking.istio.io/v1
kind: VirtualService
metadata:
  name: direct-cnn-through-egress-gateway
spec:
  hosts:
  - edition.cnn.com
  gateways:
  - mesh
  - istio-egressgateway
  tls:
  - match:
    - gateways:
      - mesh
      port: 443
      sniHosts:
      - edition.cnn.com
    route:
    - destination:
        host: istio-egressgateway.istio-system.svc.cluster.local
        subset: cnn
        port:
          number: 443
  - match:
    - gateways:
      - istio-egressgateway
      port: 443
      sniHosts:
      - edition.cnn.com
    route:
    - destination:
        host: edition.cnn.com
        port:
          number: 443
      weight: 100
EOF

  1. Send an HTTPS request to https://edition.cnn.com/politics. The output should be the same as before.

    $ kubectl exec "$SOURCE_POD" -c curl -- curl -sSL -o /dev/null -D - https://edition.cnn.com/politics
...
HTTP/2 200
Content-Type: text/html; charset=utf-8
...

  2. 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 curl 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 curl sample to the test-egress namespace.

    Zip
    $ kubectl apply -n test-egress -f @samples/curl/curl.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=curl -o jsonpath={.items..metadata.name})" -n test-egress
NAME                     READY     STATUS    RESTARTS   AGE
curl-776b7bcdcd-z7mc4    1/1       Running   0          18m

  5. Send an HTTPS request to https://edition.cnn.com/politics from the curl pod in the test-egress namespace. The request will succeed since you did not define any restrictive policies yet.

    $ kubectl exec "$(kubectl get pod -n test-egress -l app=curl -o jsonpath={.items..metadata.name})" -n test-egress -c curl -- curl -s -o /dev/null -w "%{http_code}\n"  https://edition.cnn.com/politics
200

  6. Label the namespaces where the Istio control plane and egress gateway are running. If you deployed Istio in the istio-system namespace, the command is:

$ kubectl label namespace istio-system istio=system

  1. Label the kube-system namespace.

    $ kubectl label ns kube-system kube-system=true

  2. Define a NetworkPolicy to limit the egress traffic from the test-egress namespace to traffic destined to the control plane, gateway, 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

  1. 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 curl pod cannot bypass the egress gateway. The only way it can access edition.cnn.com is by using an Istio sidecar proxy and by directing the traffic to the egress gateway. 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 "$(kubectl get pod -n test-egress -l app=curl -o jsonpath={.items..metadata.name})" -n test-egress -c curl -- curl -v -sS 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

  2. Now inject an Istio sidecar proxy into the curl 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

  3. Then redeploy the curl deployment:

    Zip
    $ kubectl delete deployment curl -n test-egress
$ kubectl apply -f @samples/curl/curl.yaml@ -n test-egress

  4. 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=curl -o jsonpath={.items..metadata.name})" -n test-egress -o jsonpath='{.spec.containers[*].name}'
curl istio-proxy

Before proceeding, you’ll need to create a similar destination rule as the one used for the curl pod in the default namespace, to direct the test-egress namespace traffic through the egress gateway:

$ kubectl apply -n test-egress -f - <<EOF
apiVersion: networking.istio.io/v1
kind: DestinationRule
metadata:
  name: egressgateway-for-cnn
spec:
  host: istio-egressgateway.istio-system.svc.cluster.local
  subsets:
  - name: cnn
EOF

  1. Send an HTTPS request to https://edition.cnn.com/politics. Now it should succeed since the traffic flows to the egress gateway is allowed by the Network Policy you defined. The gateway then forwards the traffic to edition.cnn.com.

    $ kubectl exec "$(kubectl get pod -n test-egress -l app=curl -o jsonpath={.items..metadata.name})" -n test-egress -c curl -- curl -sS -o /dev/null -w "%{http_code}\n" https://edition.cnn.com/politics
200

  2. 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:

[2020-03-06T18:12:33.101Z] "- - -" 0 - "-" "-" 906 1352475 35 - "-" "-" "-" "-" "151.101.193.67:443" outbound|443||edition.cnn.com 172.30.223.53:39460 172.30.223.53:443 172.30.223.58:38138 edition.cnn.com -

Cleanup network policies

  1. Delete the resources created in this section:
Zip
$ kubectl delete -f @samples/curl/curl.yaml@ -n test-egress
$ kubectl delete destinationrule egressgateway-for-cnn -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
  1. Follow the steps in the Cleanup HTTPS gateway section.

Cleanup

Shutdown the curl service:

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