Fault Injection

5 minute read

This task shows you how to inject faults to test the resiliency of your application.

Before you begin

Set up Istio by following the instructions in the Installation guide.
Deploy the Bookinfo sample application including the default destination rules.
Review the fault injection discussion in the Traffic Management concepts doc.

Apply application version routing by either performing the request routing task or by running the following commands:

$ kubectl apply -f @samples/bookinfo/networking/virtual-service-all-v1.yaml@
$ kubectl apply -f @samples/bookinfo/networking/virtual-service-reviews-test-v2.yaml@

With the above configuration, this is how requests flow:
- productpage → reviews:v2 → ratings (only for user jason)
- productpage → reviews:v1 (for everyone else)

Injecting an HTTP delay fault

To test the Bookinfo application microservices for resiliency, inject a 7s delay between the reviews:v2 and ratings microservices for user jason. This test will uncover a bug that was intentionally introduced into the Bookinfo app.

Note that the reviews:v2 service has a 10s hard-coded connection timeout for calls to the ratings service. Even with the 7s delay that you introduced, you still expect the end-to-end flow to continue without any errors.

Create a fault injection rule to delay traffic coming from the test user jason.

$ kubectl apply -f @samples/bookinfo/networking/virtual-service-ratings-test-delay.yaml@

Confirm the rule was created:

$ kubectl get virtualservice ratings -o yaml
apiVersion: networking.istio.io/v1alpha3
kind: VirtualService
metadata:
  name: ratings
  ...
spec:
  hosts:
  - ratings
  http:
  - fault:
      delay:
        fixedDelay: 7s
        percent: 100
    match:
    - headers:
        end-user:
          exact: jason
    route:
    - destination:
        host: ratings
        subset: v1
  - route:
    - destination:
        host: ratings
        subset: v1

Allow several seconds for the new rule to propagate to all pods.

Testing the delay configuration

Open the Bookinfo web application in your browser.
On the /productpage web page, log in as user jason.
You expect the Bookinfo home page to load without errors in approximately 7 seconds. However, there is a problem: the Reviews section displays an error message:
```
Error fetching product reviews!
Sorry, product reviews are currently unavailable for this book.
```
View the web page response times:
1. Open the Developer Tools menu in you web browser.
2. Open the Network tab
3. Reload the /productpage web page. You will see that the page actually loads in about 6 seconds.

Understanding what happened

You’ve found a bug. There are hard-coded timeouts in the microservices that have caused the reviews service to fail.

As expected, the 7s delay you introduced doesn’t affect the reviews service because the timeout between the reviews and ratings service is hard-coded at 10s. However, there is also a hard-coded timeout between the productpage and the reviews service, coded as 3s + 1 retry for 6s total. As a result, the productpage call to reviews times out prematurely and throws an error after 6s.

Bugs like this can occur in typical enterprise applications where different teams develop different microservices independently. Istio’s fault injection rules help you identify such anomalies without impacting end users.

Fixing the bug

You would normally fix the problem by:

Either increasing the productpage to reviews service timeout or decreasing the reviews to ratings timeout
Stopping and restarting the fixed microservice
Confirming that the /productpage web page returns its response without any errors.

However, you already have a fix running in v3 of the reviews service. The reviews:v3 service reduces the reviews to ratings timeout from 10s to 2.5s so that it is compatible with (less than) the timeout of the downstream productpage requests.

If you migrate all traffic to reviews:v3 as described in the traffic shifting task, you can then try to change the delay rule to any amount less that 2.5s, for example 2s, and confirm that the end-to-end flow continues without any errors.

Injecting an HTTP abort fault

Another way to test microservice resiliency is to introduce an HTTP abort fault. In this task, you will introduce an HTTP abort to the ratings microservices for the test user jason.

In this case, you expect the page to load immediately and display the Ratings service is currently unavailable message.

Create a fault injection rule to send an HTTP abort for user jason:

$ kubectl apply -f @samples/bookinfo/networking/virtual-service-ratings-test-abort.yaml@

Confirm the rule was created:

$ kubectl get virtualservice ratings -o yaml
apiVersion: networking.istio.io/v1alpha3
kind: VirtualService
metadata:
  name: ratings
  ...
spec:
  hosts:
  - ratings
  http:
  - fault:
      abort:
        httpStatus: 500
        percent: 100
    match:
    - headers:
        end-user:
          exact: jason
    route:
    - destination:
        host: ratings
        subset: v1
  - route:
    - destination:
        host: ratings
        subset: v1

Testing the abort configuration

Open the Bookinfo web application in your browser.
On the /productpage, log in as user jason.
If the rule propagated successfully to all pods, the page loads immediately and the Ratings service is currently unavailable message appears.
If you log out from user jason or open the Bookinfo application in an anonymous window (or in another browser), you will see that /productpage still calls reviews:v1 (which does not call ratings at all) for everybody but jason. Therefore you will not see any error message.

Cleanup

Remove the application routing rules:

$ kubectl delete -f @samples/bookinfo/networking/virtual-service-all-v1.yaml@

If you are not planning to explore any follow-on tasks, refer to the Bookinfo cleanup instructions to shutdown the application.