Control Egress Traffic

By default, Istio-enabled services are unable to access URLs outside of the cluster because the pod uses iptables to transparently redirect all outbound traffic to the sidecar proxy, which only handles intra-cluster destinations.

This task describes how to configure Istio to expose external services to Istio-enabled clients. You'll learn how to enable access to external services by defining ServiceEntry configurations, or alternatively, to bypass the Istio proxy for a specific range of IPs.

Before you begin

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

• Start the sleep sample which you use as a test source for external calls.

  If you have enabled automatic sidecar injection, deploy the sleep application:

  $ kubectl apply -f @samples/sleep/sleep.yaml@

  Otherwise, you have to manually inject the sidecar before deploying the sleep application:

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

  Note that any pod that you can exec and curl from will do for the procedures below.

Configuring Istio external services

Using Istio ServiceEntry configurations, you can access any publicly accessible service from within your Istio cluster. In this task you access httpbin.org and www.google.com as examples.

Configuring the external services

1. Create a ServiceEntry to allow access to an external HTTP service:

   cat <<EOF | kubectl apply -f -
   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
   EOF

2. Create a ServiceEntry and a VirtualService to allow access to an external HTTPS service. Note that for TLS protocols, including HTTPS, the TLS VirtualService is required in addition to the ServiceEntry.

   cat <<EOF | kubectl apply -f -
   apiVersion: networking.istio.io/v1alpha3
   kind: ServiceEntry
   metadata:
     name: google
   spec:
     hosts:
     - www.google.com
     ports:
     - number: 443
       name: https
       protocol: HTTPS
     resolution: DNS
     location: MESH_EXTERNAL
   ---
   apiVersion: networking.istio.io/v1alpha3
   kind: VirtualService
   metadata:
     name: google
   spec:
     hosts:
     - www.google.com
     tls:
     - match:
       - port: 443
         sni_hosts:
         - www.google.com
       route:
       - destination:
           host: www.google.com
           port:
             number: 443
         weight: 100
   EOF

Make requests to the external services

1. Exec into the pod being used as the test source. For example, if you are using the sleep service, run the following commands:

   $ export SOURCE_POD=$(kubectl get pod -l app=sleep -o jsonpath={.items..metadata.name})
   $ kubectl exec -it $SOURCE_POD -c sleep bash

2. Make a request to the external HTTP service:

   $ curl http://httpbin.org/headers

3. Make a request to the external HTTPS service:

   $ curl https://www.google.com

Setting route rules on an external service

Similar to inter-cluster requests, Istio routing rules can also be set for external services that are accessed using ServiceEntry configurations. In this example, you use istioctl to set a timeout rule on calls to the httpbin.org service.

1. From inside the pod being used as the test source, make a curl request to the /delay endpoint of the httpbin.org external service:

   $ kubectl exec -it $SOURCE_POD -c sleep bash
   $ time curl -o /dev/null -s -w "%{http_code}\n" http://httpbin.org/delay/5
   200
   
   real    0m5.024s
   user    0m0.003s
   sys     0m0.003s

   The request should return 200 (OK) in approximately 5 seconds.

2. Exit the source pod and use istioctl to set a 3s timeout on calls to the httpbin.org external service:

   cat <<EOF | kubectl apply -f -
   apiVersion: networking.istio.io/v1alpha3
   kind: VirtualService
   metadata:
     name: httpbin-ext
   spec:
     hosts:
       - httpbin.org
     http:
     - timeout: 3s
       route:
         - destination:
             host: httpbin.org
           weight: 100
   EOF

3. Wait a few seconds, then make the curl request again:

   $ kubectl exec -it $SOURCE_POD -c sleep bash
   $ time curl -o /dev/null -s -w "%{http_code}\n" http://httpbin.org/delay/5
   504
   
   real    0m3.149s
   user    0m0.004s
   sys     0m0.004s

   This time a 504 (Gateway Timeout) appears after 3 seconds. Although httpbin.org was waiting 5 seconds, Istio cut off the request at 3 seconds.

Calling external services directly

If you want to completely bypass Istio for a specific IP range, you can configure the Envoy sidecars to prevent them from intercepting the external requests. This can be done by setting the global.proxy.includeIPRanges variable of Helm and updating the ConfigMap istio-sidecar-injector by using kubectl apply. After istio-sidecar-injector is updated, the value of global.proxy.includeIPRanges will affect all the future deployments of the application pods.

The simplest way to use the global.proxy.includeIPRanges variable is to pass it the IP range(s) used for internal cluster services, thereby excluding external IPs from being redirected to the sidecar proxy. The values used for internal IP range(s), however, depends on where your cluster is running. For example, with Minikube the range is 10.0.0.1/24, so you would update your ConfigMap istio-sidecar-injector like this:

$ helm template install/kubernetes/helm/istio <the flags you used to install Istio> --set global.proxy.includeIPRanges="10.0.0.1/24" -x templates/sidecar-injector-configmap.yaml | kubectl apply -f -

Note that you should use the same Helm command you used to install Istio, in particular, the same value of the --namespace flag. In addition to the flags you used to install Istio, add --set global.proxy.includeIPRanges="10.0.0.1/24" -x templates/sidecar-injector-configmap.yaml.

Redeploy the sleep application as described in the Before you begin section.

Set the value of global.proxy.includeIPRanges

Set the value of global.proxy.includeIPRanges according to your cluster provider.

IBM Cloud Private

1. Get your service_cluster_ip_range from IBM Cloud Private configuration file under cluster/config.yaml:

   $ cat cluster/config.yaml | grep service_cluster_ip_range

   The following is a sample output:

   service_cluster_ip_range: 10.0.0.1/24

2. Use --set global.proxy.includeIPRanges="10.0.0.1/24"

IBM Cloud Kubernetes Service

Use --set global.proxy.includeIPRanges="172.30.0.0/16\,172.21.0.0/16\,10.10.10.0/24"

Google Container Engine (GKE)

The ranges are not fixed, so you will need to run the gcloud container clusters describe command to determine the ranges to use. For example:

$ gcloud container clusters describe XXXXXXX --zone=XXXXXX | grep -e clusterIpv4Cidr -e servicesIpv4Cidr
clusterIpv4Cidr: 10.4.0.0/14
servicesIpv4Cidr: 10.7.240.0/20

Use --set global.proxy.includeIPRanges="10.4.0.0/14\,10.7.240.0/20"

Azure Container Service(ACS)

Use --set global.proxy.includeIPRanges="10.244.0.0/16\,10.240.0.0/16

Minikube

Use --set global.proxy.includeIPRanges="10.0.0.1/24"

Access the external services

After updating the ConfigMap istio-sidecar-injector and redeploying the sleep application, the Istio sidecar will only intercept and manage internal requests within the cluster. Any external request bypasses the sidecar and goes straight to its intended destination. For example:

$ export SOURCE_POD=$(kubectl get pod -l app=sleep -o jsonpath={.items..metadata.name})
$ kubectl exec -it $SOURCE_POD -c sleep curl http://httpbin.org/headers

Understanding what happened

In this task you looked at two ways to call external services from an Istio mesh:

1. Using a ServiceEntry (recommended).

2. Configuring the Istio sidecar to exclude external IPs from its remapped IP table.

The first approach, using ServiceEntry, lets you use all of the same Istio service mesh features for calls to services inside or outside of the cluster. You saw this by setting a timeout rule for calls to an external service.

The second approach bypasses the Istio sidecar proxy, giving your services direct access to any external URL. However, configuring the proxy this way does require cluster provider specific knowledge and configuration.

Security note

Note that configuration examples in this task do not enable secure egress traffic control in Istio. A malicious application can bypass the Istio sidecar proxy and access any external service without Istio control.

To implement egress traffic control in a secure way, you must direct egress traffic through an egress gateway and address the security concerns expressed in Configure an Egress Gateway example, Additional Security Considerations.

Cleanup

1. Remove the rules:

   $ kubectl delete serviceentry httpbin-ext google
   $ kubectl delete virtualservice httpbin-ext google

2. Shutdown the sleep service:

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

3. Update the ConfigMap istio-sidecar-injector to redirect all outbound traffic to the sidecar proxies:

   $ helm template install/kubernetes/helm/istio <the flags you used to install Istio> -x templates/sidecar-injector-configmap.yaml | kubectl apply -f -

See also