Traffic routing

This chapter presents how to configure version routing between services in the mesh.

Outline

In this chapter you will learn:

• What are DestinationRule and VirtualService policies.
• How to route the traffic to a specific service version.

Walkthrough

Open the Kiali dashboard:

$ istioctl dashboard kiali

Then, switch to the graph view and select Versioned app graph type from the graph dropdown. It should display a similar structure:

Note that due to multiple versions of some application services, traffic is distributed to all versions using Round Robin balancing algorithm. In case, each service version implements different business logic, balancing traffic to all versions can potentially lead to undesirable side effects and harm user experience. Typically, we should strive to handle user traffic only through one version of the service.

Route traffic to a specific app version

Let's start with the shippingservice.

First, inspect the shippingservice deployments:

$ kubectl -n default describe deploy shippingservice-v1

Name:                   shippingservice-v1
Namespace:              default
...
Pod Template:
  Labels:  app=shippingservice
           version=v1
...

$ kubectl -n default describe deploy shippingservice-v2

Name:                   shippingservice-v2
Namespace:              default
...
Pod Template:
  Labels:  app=shippingservice
           version=v2
...

Note that pods produced by these deployments have labels determining the service version: version=v1 and version=v2.

In order to enforce routing the user traffic to version v1 of the shipping service, apply the DestinationRule and VirtualService policies:

$ kubectl -n default apply -f ./release/istio/shippingservice-dr.yaml
destinationrule.networking.istio.io/shippingservice created
$ kubectl -n default apply -f ./release/istio/shippingservice-vs.yaml
virtualservice.networking.istio.io/shippingservice created

The former uses pod labels to specify named service subsets which group service endpoints by version:

$ kubectl -n default describe dr shippingservice

Name:         shippingservice
Namespace:    default
...
Spec:
  Host:  shippingservice
  Subsets:
    Labels:
      Version:  v1
    Name:       v1
    Labels:
      Version:  v2
    Name:       v2
    Labels:
      Version:  v3
    Name:       v3

The latter uses the defined service subsets to route the traffic to the proper service version:

$ kubectl -n default describe vs shippingservice

Name:         shippingservice
Namespace:    default
...
Spec:
  Hosts:
    shippingservice
  Http:
    Route:
      Destination:
        Host:    shippingservice
        Subset:  v1

After applying the policies, the traffic should be routed only to the version v1 of the shipping service:

It might take a while until the configuration is distributed to the proxies and Kiali infers new comunication pattern from collected metrics. Changing the time range in the selector might reduce the time needed to obtain expected results in the graph:

The service node in the graph should be marked with a purple virtual service icon.

Exercises

1. Apply DestinationRule and VirtualService policies to all services deployed in the service mesh regardless of how many versions each service provides. Route the traffic to version v1 of each service.

2. Route productcatelog traffic to version v2.