Enabling Egress Traffic

By default, Istio-enabled services are unable to access URLs outside of the cluster because iptables is used in the pod 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 configure an external service and make requests to it via the Istio egress service or, alternatively, to simply enable direct calls to an external service.

Before you begin

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

  • Start the sleep sample which will be used as a test source for external calls.

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

    Note that any pod that you can exec and curl from would do.

Using the Istio Egress service

Using the Istio Egress service, you can access any publicly accessible service from within your Istio cluster. In this task we will use httpbin.org and www.google.com as examples.

Configuring the external services

  1. Register an external HTTP service:

    cat <<EOF | kubectl create -f -
    apiVersion: v1
    kind: Service
    metadata:
     name: externalbin
    spec:
     type: ExternalName
     externalName: httpbin.org
     ports:
     - port: 80
       # important to set protocol name
       name: http
    EOF
    
  2. Register an external HTTPS service:

    cat <<EOF | kubectl create -f -
    apiVersion: v1
    kind: Service
    metadata:
     name: securegoogle
    spec:
     type: ExternalName
     externalName: www.google.com
     ports:
     - port: 443
       # important to set protocol name
       name: https
    EOF
    

The metadata.name field is the url your internal apps will use when calling the external service. The spec.externalName is the DNS name of the external service. Egress Envoy expects external services to be listening on either port 80 for HTTP or port 443 for HTTPS.

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 an external service using the name from the Service spec above followed by the path to the desired API endpoint:

    curl http://externalbin/headers
    
  3. For external services of type HTTPS, the port must be specified in the request. App clients should make the request over HTTP since the Egress Envoy will initiate HTTPS with the external service:

    curl http://securegoogle:443
    

Calling external services directly

The Istio Egress service currently only supports HTTP/HTTPS requests. If you want to access services with other protocols (e.g., mongodb://host/database), or if you simply don’t want to use the Egress proxy, you will need to configure the source service’s Envoy sidecar to prevent it from intercepting the external requests. This can be done using the --includeIPRanges option of istioctl kube-inject when starting the service.

The simplest way to use the --includeIPRanges option 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 start the sleep service like this:

kubectl apply -f <(istioctl kube-inject -f samples/apps/sleep/sleep.yaml --includeIPRanges=10.0.0.1/24)

On IBM Bluemix, use:

kubectl apply -f <(istioctl kube-inject -f samples/apps/sleep/sleep.yaml --includeIPRanges=172.30.0.0/16,172.20.0.0/16,10.10.10.0/24)

On 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
kubectl apply -f <(istioctl kube-inject -f samples/apps/sleep/sleep.yaml --includeIPRanges=10.4.0.0/14,10.7.240.0/20)

On Azure Container Service(ACS), use:

kubectl apply -f <(istioctl kube-inject -f samples/apps/sleep/sleep.yaml --includeIPRanges=10.244.0.0/16,10.240.0.0/16)

After starting your service this way, the Istio sidecar will only intercept and manage internal requests within the cluster. Any external request will simply bypass the sidecar and go straight to its intended destination.

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 we looked at two ways to call external services from within an Istio cluster:

  1. Using the Istio egress service (recommended)

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

The first approach (Egress service) currently only supports HTTP(S) requests, but allows you to use all of the same Istio service mesh features for calls to services within or outside of the cluster.

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 cloud provider specific knowledge and configuration.

Cleanup

  1. Remove the external services.

    kubectl delete service externalbin securegoogle 
    
  2. Shutdown the sleep service.

    kubectl delete -f samples/apps/sleep/sleep.yaml
    

What’s next