Mirroring

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.

This task demonstrates the traffic shadowing/mirroring capabilities of Istio. Traffic mirroring is a powerful concept that allows feature teams to bring changes to production with as little risk as possible. Mirroring brings a copy of live traffic to a mirrored service and happens out of band of the critical request path for the primary service.

Before you begin

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

  • Start two versions of the httpbin service that have access logging enabled

    httpbin-v1:

        cat <<EOF | istioctl kube-inject -f - | kubectl create -f -
        apiVersion: extensions/v1beta1
        kind: Deployment
        metadata:
          name: httpbin-v1
        spec:
          replicas: 1
          template:
            metadata:
              labels:
                app: httpbin
                version: v1
            spec:
              containers:
              - image: docker.io/kennethreitz/httpbin
                imagePullPolicy: IfNotPresent
                name: httpbin
                command: ["gunicorn", "--access-logfile", "-", "-b", "0.0.0.0:8080", "httpbin:app"]
                ports:
                - containerPort: 8080
        EOF
    

    httpbin-v2:

        cat <<EOF | istioctl kube-inject -f - | kubectl create -f -
        apiVersion: extensions/v1beta1
        kind: Deployment
        metadata:
          name: httpbin-v2
        spec:
          replicas: 1
          template:
            metadata:
              labels:
                app: httpbin
                version: v2
            spec:
              containers:
              - image: docker.io/kennethreitz/httpbin
                imagePullPolicy: IfNotPresent
                name: httpbin
                command: ["gunicorn", "--access-logfile", "-", "-b", "0.0.0.0:8080", "httpbin:app"]
                ports:
                - containerPort: 8080
        EOF
    

    httpbin Kubernetes service:

        cat <<EOF | kubectl create -f -
        apiVersion: v1
        kind: Service
        metadata:
          name: httpbin
          labels:
            app: httpbin
        spec:
          ports:
          - name: http
            port: 8080
          selector:
            app: httpbin
        EOF
    
  • Start the sleep service so we can use curl to provide load

    sleep service:

        cat <<EOF | istioctl kube-inject -f - | kubectl create -f -
        apiVersion: extensions/v1beta1
        kind: Deployment
        metadata:
          name: sleep
        spec:
          replicas: 1
          template:
            metadata:
              labels:
                app: sleep
            spec:
              containers:
              - name: sleep
                image: tutum/curl
                command: ["/bin/sleep","infinity"]
                imagePullPolicy: IfNotPresent
        EOF
    

Mirroring

Let’s set up a scenario to demonstrate the traffic-mirroring capabilities of Istio. We have two versions of our httpbin service. By default Kubernetes will load balance across both versions of the service. We’ll use Istio to force all traffic to v1 of the httpbin service.

Creating default routing policy

  1. Create a default route rule to route all traffic to v1 of our httpbin service:

        cat <<EOF | istioctl create -f -
        apiVersion: networking.istio.io/v1alpha3
        kind: VirtualService
        metadata:
          name: httpbin
        spec:
          hosts:
            - httpbin
          http:
          - route:
            - destination:
                host: httpbin
                subset: v1
              weight: 100
        ---
        apiVersion: networking.istio.io/v1alpha3
        kind: DestinationRule
        metadata:
          name: httpbin
        spec:
          host: httpbin
          subsets:
          - name: v1
            labels:
              version: v1
          - name: v2
            labels:
              version: v2
        EOF
    

    Now all traffic should go to httpbin v1 service. Let’s try sending in some traffic:

    $ export SLEEP_POD=$(kubectl get pod -l app=sleep -o jsonpath={.items..metadata.name})
    $ kubectl exec -it $SLEEP_POD -c sleep -- sh -c 'curl  http://httpbin:8080/headers' | python -m json.tool
    {
      "headers": {
        "Accept": "*/*",
        "Content-Length": "0",
        "Host": "httpbin:8080",
        "User-Agent": "curl/7.35.0",
        "X-B3-Sampled": "1",
        "X-B3-Spanid": "eca3d7ed8f2e6a0a",
        "X-B3-Traceid": "eca3d7ed8f2e6a0a",
        "X-Ot-Span-Context": "eca3d7ed8f2e6a0a;eca3d7ed8f2e6a0a;0000000000000000"
      }
    }
    

    If we check the logs for v1 and v2 of our httpbin pods, we should see access log entries for only v1:

    $ export V1_POD=$(kubectl get pod -l app=httpbin,version=v1 -o jsonpath={.items..metadata.name})
    $ kubectl logs -f $V1_POD -c httpbin
    127.0.0.1 - - [07/Mar/2018:19:02:43 +0000] "GET /headers HTTP/1.1" 200 321 "-" "curl/7.35.0"
    
    $ export V2_POD=$(kubectl get pod -l app=httpbin,version=v2 -o jsonpath={.items..metadata.name})
    $ kubectl logs -f $V2_POD -c httpbin
    <none>
    
  2. Change the route rule to mirror traffic to v2

        cat <<EOF | istioctl replace -f -
        apiVersion: networking.istio.io/v1alpha3
        kind: VirtualService
        metadata:
          name: httpbin
        spec:
          hosts:
            - httpbin
          http:
          - route:
            - destination:
                host: httpbin
                subset: v1
              weight: 100
            mirror:
              host: httpbin
              subset: v2
        EOF
    

    This route rule specifies we route 100% of the traffic to v1. The last stanza specifies we want to mirror to the httpbin v2 service. When traffic gets mirrored, the requests are sent to the mirrored service with its Host/Authority header appended with -shadow. For example, cluster-1 becomes cluster-1-shadow. Also important to realize is that these requests are mirrored as “fire and forget”, i.e., the responses are discarded.

    Now if we send in traffic:

    $ kubectl exec -it $SLEEP_POD -c sleep -- sh -c 'curl  http://httpbin:8080/headers' | python -m json.tool
    

    We should see access logging for both v1 and v2. The access logs created in v2 is the mirrored requests that are actually going to v1.

    $ kubectl logs -f $V1_POD -c httpbin
    127.0.0.1 - - [07/Mar/2018:19:02:43 +0000] "GET /headers HTTP/1.1" 200 321 "-" "curl/7.35.0"
    127.0.0.1 - - [07/Mar/2018:19:26:44 +0000] "GET /headers HTTP/1.1" 200 321 "-" "curl/7.35.0"
    
    $ kubectl logs -f $V2_POD -c httpbin
    127.0.0.1 - - [07/Mar/2018:19:26:44 +0000] "GET /headers HTTP/1.1" 200 361 "-" "curl/7.35.0"
    

Cleaning up

  1. Remove the rules.

    $ istioctl delete virtualservice httpbin
    $ istioctl delete destinationrule httpbin
    
  2. Shutdown the httpbin service and client.

    $ kubectl delete deploy httpbin-v1 httpbin-v2 sleep
    $ kubectl delete svc httpbin
    

What’s next

Check out the Mirroring configuration reference documentation.