This is a very simple example of how to create a sticky session configuration for a application running behind istio

destinationrule.yaml

---
apiVersion: networking.istio.io/v1beta1
kind: DestinationRule
metadata:
  name: <app-name>
spec:
  host: <app-name>.<app-namespace>.svc.cluster.local
  trafficPolicy:
    loadBalancer:
      consistentHash:
        httpCookie:
          name: cookie
          path: <cookie to use for sessions>
          ttl: "3600s"

virtualservice.yaml

---
apiVersion: networking.istio.io/v1alpha3
kind: VirtualService
metadata:
  name: <app-name>
  namespace: istio-system
spec:
  hosts:
  - <host>
  gateways:
  - <gateway-name>
  http:
  - match:
    - uri:
        prefix: /
    route:
    - destination:
        port:
          number: 80
        host: <app-name>.<app-namespace>.svc.cluster.local