Canary Deployment with Kubernetes and Istio

Istio i

s of Istio's traffic management capabilities:

• Virtual Service: Virtual Service describes how traffic flows to a set of destinations. Using Virtual Service you can configure how to route the requests to a service within the mesh. It contains a bunch of routing rules that are evaluated, and then a decision is made on where to route the incoming request (or even reject if no routes match).

• Gateway: Gateways are used to manage your inbound and outbound traffic. They allow you to specify the virtual hosts and their associated ports that needs to be opened for allowing the traffic into the cluster.

• Destination Rule: This is used to configure how a client in the mesh interacts with your service. It's used for configuring TLS settings of your sidecar, splitting your service into subs

  ets, load balancing strategy for your clients etc.

For doing canary deployment, destination rule plays a major role as that's what we will be using to split the service into subset and route traffic accordingly.

Application deployment

For our canary deployment, we will be using the following version of the application:

• httpbin.org: This will be the version one (v1) of our application. This is the application that's already deployed, and your aim is to partially replace it with a newer version of the application.

• websocket app: This will be the version two (v2) of the application that has to be gradually introduced.

Note that in the actual real world, both the applications will share the same code. For our example, we are just taking two arbitrary applications to make testing easier.

Our assumption is that we already have version one of our application deployed. So let's deploy that initially. We will write our usual Kubernetes resources for it. The deployment manifest for the version one application:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: httpbin
  namespace: canary
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
        ports:
        - containerPort: 80

And let's create a corresponding service for it:

apiVersion: v1
kind: Service
metadata:
  labels:
    app: httpbin
  name: httpbin
  namespace: canary
spec:
  ports:
  - name: httpbin
    port: 8000
    targetPort: 80
  - name: tornado
    port: 8001
    targetPort: 8888
  selector:
    app: httpbin
  type

SSL certificate for the application which will use cert-manager:

apiVersion: cert-manager.io/v1
kind: Certificate
metadata:
  name: httpbin-ingress-cert
  namespace: istio-system
spec:
  secretName: httpbin-ingress-cert
  issuerRef:
    name: letsencrypt-dns-prod
    kind: ClusterIssuer
  dnsNames

And the Istio resources for the application:

apiVersion: networking.istio.io/v1alpha3
kind: Gateway
metadata:
  name: httpbin-gateway
  namespace: canary
spec:
  selector:
    istio: ingressgateway
  servers:
  - hosts:
    - canary.33test.dev-sandbox.fpcomplete.com
    port:
      name: https-httpbin
      number: 443
      protocol: HTTPS
    tls:
      credentialName: httpbin-ingress-cert
      mode: SIMPLE
  - hosts:
    - canary.33test.dev-sandbox.fpcomplete.com
    port:
      name: http-httpbin
      number: 80
      protocol: HTTP
    tls:
      httpsRedirect: true
---
apiVersion: networking.istio.io/v1alpha3
kind: VirtualService
metadata:
  name: httpbin
  namespace: canary
spec:
  gateways:
  - httpbin-gateway
  hosts:
  - canary.33test.dev-sandbox.fpcomplete.com
  http:
  - route:
    - destination:
        host: httpbin.canary.svc.cluster.local
        port:
          number: 8000

The above resource define gateway and virtual service. You could see that we are using TLS here and redirecting HTTP to HTTPS.

We also have to make sure that namespace has istio injection enabled:

apiVersion: v1
kind: Namespace
metadata:
  labels:
    app.kubernetes.io/component: httpbin
    istio-injection: enabled
  name

I have the above set of k8s resources managed via kustomize. Let's deploy them to get the initial environment which consists of only v1 (httpbin) application:

❯ kustomize build overlays/istio_canary > istio.yaml
❯ kubectl apply -f istio.yaml
namespace/canary created
service/httpbin created
deployment.apps/httpbin created
gateway.networking.istio.io/httpbin-gateway created
virtualservice.networking.istio.io/httpbin created
❯ kubectl apply -f overlays/istio_canary/certificate.yaml
certificate.cert-manager.io/httpbin-ingress-cert created

Now I can go and verify in my browser that my application is actually up and running:

Now comes the interesting part. We have to deploy the version two of our application and make sure around 20% of our traffic goes to it. Let's write the deployment manifest for it:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: httpbin-v2
  namespace: canary
spec:
  replicas: 1
  selector:
    matchLabels:
      app: httpbin
      version: v2
  template:
    metadata:
      labels:
        app: httpbin
        version: v2
    spec:
      containers:
      - image: psibi/tornado-websocket:v0.3
        imagePullPolicy: IfNotPresent
        name: tornado
        ports:
        - containerPort: 8888

And now the destination rule to split the service:

apiVersion: networking.istio.io/v1alpha3
kind: DestinationRule
metadata:
  name: httpbin
  namespace: canary
spec:
  host: httpbin.canary.svc.cluster.local
  subsets:
  - labels:
      version: v1
    name: v1
  - labels:
      version: v2
    name

And finally let's modify the virtual service to split 20% of the traffic to the newer version:

apiVersion: networking.istio.io/v1alpha3
kind: VirtualService
metadata:
  name: httpbin
  namespace: canary
spec:
  gateways:
  - httpbin-gateway
  hosts:
  - canary.33test.dev-sandbox.fpcomplete.com
  http:
  - route:
    - destination:
        host: httpbin.canary.svc.cluster.local
        port:
          number: 8000
        subset: v1
      weight: 80
    - destination:
        host: httpbin.canary.svc.cluster.local
        port:
          number: 8001
        subset: v2
      weight: 20

And now if you go again to the browser and refresh it a number of times (note that we route only 20% of the traffic to the new deployment), you will see the new application eventually:

Testing deployment

Let's do around 10 curl requests to our endpoint to see how the traffic is getting routed:

❯ seq 10 | xargs -Iz curl -s https://canary.33test.dev-sandbox.fpcomplete.com | rg "<title>"
    <title>httpbin.org</title>
    <title>httpbin.org</title>
    <title>httpbin.org</title>
<title>tornado WebSocket example</title>
    <title>httpbin.org</title>
    <title>httpbin.org</title>
    <title>httpbin.org</title>
    <title>httpbin.org</title>
    <title>httpbin.org</title>
<title>tornado WebSocket example</title>

And you can confirm how out of the 10 requests, 2 requests are routed to the websocket (v2) application. If you have Kiali deployed, you can even visualize the above traffic flow:

And that summarizes our post on how to achieve canary deployment using Istio. While this post shows a basic example, traffic steering and routing is one of the core features of Istio and it offers various ways to configure the routing decisions made by it. You can find more further details about it in the official docs. You can also use a controller like Argo Rollouts with Istio to perform canary deployments and use additional features like analysis and experiment.