Control Egress TCP Traffic

The Control Egress Traffic task demonstrated how external (outside the Kubernetes cluster) HTTP and HTTPS services can be accessed from applications inside the mesh. To remind: by default, Istio-enabled applications are unable to access URLs outside the cluster. To enable such access, egress rules must be defined, or, alternatively, direct access to external services must be configured.

This task describes how to configure Istio to expose external TCP services to applications inside the Istio service mesh.

Before you begin

Setup Istio by following the instructions in the Installation guide.
Start the sleep sample application which will be used as a test source for external calls.
```
kubectl apply -f <(istioctl kube-inject -f samples/sleep/sleep.yaml)
```
Note that any pod that you can execute curl from, would do.

Using Istio egress rules for external TCP traffic

In this task we access wikipedia.org by HTTPS originated by the application. This task demonstrates the use case when the application cannot use HTTP with TLS origination by the sidecar proxy. Using HTTP with TLS origination by the sidecar proxy is described in the Control Egress Traffic task. In that task, https://google.com was accessed by issuing HTTP requests to http://www.google.com:443.

The HTTPS traffic originated by the application will be treated by Istio as opaque TCP. To enable such traffic, we define a TCP egress rule on port 443.

In TCP egress rules as opposed to HTTP-based egress rules, the destinations are specified by IPs or by blocks of IPs in CIDR notation.

Let’s assume for the sake of the example that we want to access wikipedia.org by the domain name. This means that we have to specify all the IPs of wikipedia.org in our TCP egress rules. Fortunately, the IPs of wikipedia.org are published here. It is a list of IP blocks in CIDR notation: 91.198.174.192/27, 103.102.166.224/27, and more. We must define an egress rule per each IP block.

Alternatively, if we want to access wikipedia.org by an IP, a single egress rule for that IP must be defined.

Creating egress rules

Let’s create egress rules to enable TCP access to wikipedia.org:

cat <<EOF | istioctl create -f -
kind: EgressRule
metadata:
  name: wikipedia-range1
spec:
  destination:
      service: 91.198.174.192/27
  ports:
      - port: 443
        protocol: tcp
---
kind: EgressRule
metadata:
  name: wikipedia-range2
spec:
  destination:
      service: 103.102.166.224/27
  ports:
      - port: 443
        protocol: tcp
---
kind: EgressRule
metadata:
  name: wikipedia-range3
spec:
  destination:
      service: 198.35.26.96/27
  ports:
      - port: 443
        protocol: tcp
---
kind: EgressRule
metadata:
  name: wikipedia-range4
spec:
  destination:
      service: 208.80.153.224/27
  ports:
      - port: 443
        protocol: tcp
---
kind: EgressRule
metadata:
  name: wikipedia-range5
spec:
  destination:
      service: 208.80.154.224/27
  ports:
      - port: 443
        protocol: tcp
EOF

This command will create five egress rules, a rule per different block of IPs of wikipedia.org. Note the --- (three dashes) separator between the egress rules. It is the YAML separator between documents in a stream. It allows us to create multiple configuration artifacts using a single istioctl command.

Access wikipedia.org by HTTPS

kubectl exec into the pod to be used as the test source. If you are using the sleep application, run the following command:
```
kubectl exec -it $(kubectl get pod -l app=sleep -o jsonpath={.items..metadata.name}) -c sleep bash
```
Make a request and see that we can access https://www.wikipedia.org successfully:
```
curl -o /dev/null -s -w "%{http_code}\n" https://www.wikipedia.org
```
```
200
```
We should see 200 printed as the output, which is the HTTP code OK.

Now let’s fetch the current number of articles in English language:

curl -s https://en.wikipedia.org/wiki/Main_Page | grep articlecount | grep 'Special:Statistics'

The output should be similar to:

<div id="articlecount" style="font-size:85%;"><a href="/wiki/Special:Statistics" title="Special:Statistics">5,563,121</a> articles in <a  href="/wiki/English_language" title="English language">English</a></div>

This means there were 5,563,121 articles in Wikipedia in English when this task was written.

Cleanup

Remove the egress rules we created.

istioctl delete egressrule wikipedia-range1 wikipedia-range2 wikipedia-range3 wikipedia-range4 wikipedia-range5 -n default

Shutdown the sleep application.

kubectl delete -f samples/sleep/sleep.yaml

What’s next

The Egress Rules reference.
The Control Egress Traffic task, for HTTP and HTTPS.