Control Egress Traffic

This task uses the new v1alpha3 traffic management API. The old API has been deprecated and will be removed in the next Istio release. If you need to use the old version, follow the docs here.

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 enable access to external services by defining ServiceEntry configurations, or alternatively, to simply 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 will be used as a test source for external calls.

If you have enabled automatic sidecar injection, do
```
$ 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 would do.

Configuring Istio external services

Using Istio ServiceEntry configurations, 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

Create an ServiceEntry to allow access to an external HTTP service:

    cat <<EOF | istioctl create -f -
    apiVersion: networking.istio.io/v1alpha3
    kind: ServiceEntry
    metadata:
      name: httpbin-ext
    spec:
      hosts:
      - httpbin.org
      ports:
      - number: 80
        name: http
        protocol: HTTP
    EOF

Create an ServiceEntry to allow access to an external HTTPS service:

    cat <<EOF | istioctl create -f -
    apiVersion: networking.istio.io/v1alpha3
    kind: ServiceEntry
    metadata:
      name: google-ext
    spec:
      hosts:
      - www.google.com
      ports:
      - number: 443
        name: https
        protocol: HTTPS
    EOF

Make requests to the external services

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

Make a request to the external HTTP service:
```
$ curl http://httpbin.org/headers
```
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. To illustrate we will use istioctl to set a timeout rule on calls to the httpbin.org service.

From inside the pod being used as the test source, invoke 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.

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

    cat <<EOF | istioctl create -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

Wait a few seconds, then issue 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 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.

Determine the value of `global.proxy.includeIPRanges`

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

IBM Cloud Private

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
```
A sample output is as following:
```
service_cluster_ip_range: 10.0.0.1/24
```
Use --set global.proxy.includeIPRanges="10.0.0.1/24"

IBM Cloud Kubernetes Service

Use --set global.proxy.includeIPRanges="172.30.0.0/16\,172.20.0.0/16\,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 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 an Istio mesh:

Using a ServiceEntry (recommended)
Configuring the Istio sidecar to exclude external IPs from its remapped IP table

The first approach (ServiceEntry) allows you to use all of the same Istio service mesh features for calls to services within or outside of the cluster. We demonstrated 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 cloud provider specific knowledge and configuration.

Security note

Warning 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 task, Additional Security Considerations.

Cleanup

Remove the rules.

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

Shutdown the sleep service.

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

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 -

What's next

Learn more about service entries.
Learn how to setup timeouts, retries, and circuit breakers for egress traffic.