istio destination rule subset don't really work

 

Istio destination rule routes to a service. Then the service uses selector to match against running pods that has certain labels for example, app=version. 

When a request comes in, it goes around in a round robin fashion (depending on the weight configure) it goes to hit individual pods. 

So the subset is quite meaningless - really confusing as shown below. 

If i really wanted to change the routing behavior, all i need to do is change the deployment->spec->selector->matchLabels->version: v3 to something else. This will make it hidden from service's selector. 

If you change the app: reviews to review-3 it is elusive to the service and won't be picked up  and route stops.

This is my service configuration 

apiVersion: v1

kind: Service

metadata:

  name: reviews

  labels:

    app: reviews

    service: reviews

spec:

  ports:

  - port: 9080

    name: http

  selector:

    app: reviews

Some additional notes: 

Service selector uses pods label to decide what to managed. 

if you have 3 labels defined in your service selector, then it all needs to match to the pod

for example, if your selector has (selector not the service label - as many people tend to get confused with) 

- app: v1 

- version: v1 

- owner: v1 

then your pod label should have all these 3 defined before it can form a 'route'

In order for istio to work, we have to be very careful with spec->ports->name as it has to be http or http-web or http-config. It must start with http.

Destination rule commented out as shown below but the routing still goes to all 3 rating reviews.

apiVersion: networking.istio.io/v1alpha3

kind: DestinationRule

metadata:

  name: reviews

spec:

  host: reviews

  subsets:

  # - name: v1

  #   labels:

  #     version: v1

  # - name: v2

  #   labels:

  #     version: v2

  - name: v3

    labels:

      version: v3

    # trafficPolicy:

    #   loadBalancer:

    #      simple: LEAST_REQUEST