Mirroring

6 minute read page test

This task demonstrates the traffic mirroring capabilities of Istio.

Traffic mirroring, also called shadowing, is a powerful concept that allows feature teams to bring changes to production with as little risk as possible. Mirroring sends a copy of live traffic to a mirrored service. The mirrored traffic happens out of band of the critical request path for the primary service.

In this task, you will first force all traffic to v1 of a test service. Then, you will apply a rule to mirror a portion of traffic to v2.

Istio includes beta support for the Kubernetes Gateway API and intends to make it the default API for traffic management in the future. The following instructions allow you to choose to use either the Gateway API or the Istio configuration API when configuring traffic management in the mesh. Follow instructions under either the Gateway API or Istio APIs tab, according to your preference.

Note that this document uses the Gateway API to configure internal mesh (east-west) traffic, i.e., not just ingress (north-south) traffic. Configuring internal mesh traffic is an experimental feature of the Gateway API, currently under development and pending upstream agreement. Make sure to install the experimental CRDs before using the Gateway API:

$ kubectl kustomize "github.com/kubernetes-sigs/gateway-api/config/crd/experimental?ref=v0.6.2" | kubectl apply -f -

Before you begin

Set up Istio by following the instructions in the Installation guide.

Start by deploying two versions of the httpbin service that have access logging enabled:

httpbin-v1:

$ cat <<EOF | istioctl kube-inject -f - | kubectl create -f -
apiVersion: apps/v1
kind: Deployment
metadata:
  name: httpbin-v1
spec:
  replicas: 1
  selector:
    matchLabels:
      app: httpbin
      version: v1
  template:
    metadata:
      labels:
        app: httpbin
        version: v1
    spec:
      containers:
      - image: docker.io/kennethreitz/httpbin
        imagePullPolicy: IfNotPresent
        name: httpbin
        command: ["gunicorn", "--access-logfile", "-", "-b", "0.0.0.0:80", "httpbin:app"]
        ports:
        - containerPort: 80
EOF

httpbin-v2:

$ cat <<EOF | istioctl kube-inject -f - | kubectl create -f -
apiVersion: apps/v1
kind: Deployment
metadata:
  name: httpbin-v2
spec:
  replicas: 1
  selector:
    matchLabels:
      app: httpbin
      version: v2
  template:
    metadata:
      labels:
        app: httpbin
        version: v2
    spec:
      containers:
      - image: docker.io/kennethreitz/httpbin
        imagePullPolicy: IfNotPresent
        name: httpbin
        command: ["gunicorn", "--access-logfile", "-", "-b", "0.0.0.0:80", "httpbin:app"]
        ports:
        - containerPort: 80
EOF

httpbin Kubernetes service:

$ kubectl create -f - <<EOF
apiVersion: v1
kind: Service
metadata:
  name: httpbin
  labels:
    app: httpbin
spec:
  ports:
  - name: http
    port: 8000
    targetPort: 80
  selector:
    app: httpbin
EOF

Start the sleep service so you can use curl to provide load:

sleep service:

$ cat <<EOF | istioctl kube-inject -f - | kubectl create -f -
apiVersion: apps/v1
kind: Deployment
metadata:
  name: sleep
spec:
  replicas: 1
  selector:
    matchLabels:
      app: sleep
  template:
    metadata:
      labels:
        app: sleep
    spec:
      containers:
      - name: sleep
        image: curlimages/curl
        command: ["/bin/sleep","3650d"]
        imagePullPolicy: IfNotPresent
EOF

Creating a default routing policy

By default Kubernetes load balances across both versions of the httpbin service. In this step, you will change that behavior so that all traffic goes to v1.

Create a default route rule to route all traffic to v1 of the service:

$ kubectl apply -f - <<EOF
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

$ kubectl apply -f - <<EOF
apiVersion: v1
kind: Service
metadata:
  name: httpbin-v1
spec:
  ports:
  - port: 80
    name: http
  selector:
    app: httpbin
    version: v1
---
apiVersion: v1
kind: Service
metadata:
  name: httpbin-v2
spec:
  ports:
  - port: 80
    name: http
  selector:
    app: httpbin
    version: v2
---
apiVersion: gateway.networking.k8s.io/v1beta1
kind: HTTPRoute
metadata:
  name: httpbin
spec:
  parentRefs:
  - group: ""
    kind: Service
    name: httpbin
    port: 8000
  rules:
  - backendRefs:
    - name: httpbin-v1
      port: 80
EOF

Now, with all traffic directed to httpbin:v1, send a request to the service:

$ export SLEEP_POD=$(kubectl get pod -l app=sleep -o jsonpath={.items..metadata.name})
$ kubectl exec "${SLEEP_POD}" -c sleep -- curl -sS http://httpbin:8000/headers
{
  "headers": {
    "Accept": "*/*",
    "Content-Length": "0",
    "Host": "httpbin:8000",
    "User-Agent": "curl/7.35.0",
    "X-B3-Parentspanid": "57784f8bff90ae0b",
    "X-B3-Sampled": "1",
    "X-B3-Spanid": "3289ae7257c3f159",
    "X-B3-Traceid": "b56eebd279a76f0b57784f8bff90ae0b",
    "X-Envoy-Attempt-Count": "1",
    "X-Forwarded-Client-Cert": "By=spiffe://cluster.local/ns/default/sa/default;Hash=20afebed6da091c850264cc751b8c9306abac02993f80bdb76282237422bd098;Subject=\"\";URI=spiffe://cluster.local/ns/default/sa/default"
  }
}

Check the logs for v1 and v2 of the httpbin pods. You should see access log entries for v1 and none for v2:

$ export V1_POD=$(kubectl get pod -l app=httpbin,version=v1 -o jsonpath={.items..metadata.name})
$ kubectl logs "$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 "$V2_POD" -c httpbin
<none>

Mirroring traffic to v2

Change the route rule to mirror traffic to v2:

$ kubectl apply -f - <<EOF
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
    mirrorPercentage:
      value: 100.0
EOF

This route rule sends 100% of the traffic to v1. The last stanza specifies that you want to mirror (i.e., also send) 100% of the same traffic to the httpbin:v2 service. When traffic gets mirrored, the requests are sent to the mirrored service with their Host/Authority headers appended with -shadow. For example, cluster-1 becomes cluster-1-shadow.

Also, it is important to note that these requests are mirrored as “fire and forget”, which means that the responses are discarded.

You can use the value field under the mirrorPercentage field to mirror a fraction of the traffic, instead of mirroring all requests. If this field is absent, all traffic will be mirrored.

$ kubectl apply -f - <<EOF
apiVersion: gateway.networking.k8s.io/v1beta1
kind: HTTPRoute
metadata:
  name: httpbin
spec:
  parentRefs:
  - group: ""
    kind: Service
    name: httpbin
    port: 8000
  rules:
  - filters:
    - type: RequestMirror
      requestMirror:
        backendRef:
          name: httpbin-v2
          port: 80
    backendRefs:
    - name: httpbin-v1
      port: 80
EOF

This route rule sends 100% of the traffic to v1. The RequestMirror filter specifies that you want to mirror (i.e., also send) 100% of the same traffic to the httpbin:v2 service. When traffic gets mirrored, the requests are sent to the mirrored service with their Host/Authority headers appended with -shadow. For example, cluster-1 becomes cluster-1-shadow.

Also, it is important to note that these requests are mirrored as “fire and forget”, which means that the responses are discarded.

Send in traffic:

$ kubectl exec "${SLEEP_POD}" -c sleep -- curl -sS http://httpbin:8000/headers

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

$ kubectl logs "$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 "$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

Remove the rules:

$ kubectl delete virtualservice httpbin
$ kubectl delete destinationrule httpbin

$ kubectl delete httproute httpbin
$ kubectl delete svc httpbin-v1 httpbin-v2

Shutdown the httpbin service and client:

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