Traffic management

Learn traffic routing with Istio.

Traffic management

Istio manages traffic with two objects: a DestinationRule defines a service's subsets (e.g. versions) and connection settings; a VirtualService determines which subset requests go to and in what proportion. For a canary deployment, the new version gets a small percentage of the traffic:

apiVersion: networking.istio.io/v1
kind: DestinationRule
metadata:
  name: api
spec:
  host: api
  subsets:
    - name: v1
      labels: {surum: v1}
    - name: v2
      labels: {surum: v2}
---
apiVersion: networking.istio.io/v1
kind: VirtualService
metadata:
  name: api
spec:
  hosts: [api]
  http:
    - route:
        - destination: {host: api, subset: v1}
          weight: 90
        - destination: {host: api, subset: v2}
          weight: 10

Resilience settings

The VirtualService defines retries and timeouts; the DestinationRule defines circuit breaking (taking an instance returning too many errors out of rotation for a while):

# VirtualService
  http:
    - route: [{destination: {host: api, subset: v1}}]
      timeout: 3s
      retries:
        attempts: 3
        perTryTimeout: 1s
        retryOn: 5xx,reset,connect-failure
# DestinationRule
  trafficPolicy:
    outlierDetection:
      consecutive5xxErrors: 5
      interval: 30s
      baseEjectionTime: 60s

Exercise Canary routing

Write a VirtualService's spec section (starting with spec:): hosts: [api]; a single route under http: weight: 80 to api/v1, weight: 20 to api/v2; timeout: 3s.

Show example solution

spec:
  hosts: [api]
  http:
    - route:
        - destination:
            host: api
            subset: v1
          weight: 80
        - destination:
            host: api
            subset: v2
          weight: 20
      timeout: 3s

Test yourself

Without a mesh, how is the ratio set when doing a canary with two Deployments?
- Randomly
- With a Service weight
- It isn't possible
- By the ratio of replica counts (e.g. 9:1); with a mesh, a percentage independent of replicas is given
Show answer

By the ratio of replica counts (e.g. 9:1); with a mesh, a percentage independent of replicas is given — A Kubernetes Service has no weight field.

Write the share of traffic going to the new version.

        - destination: {host: api, subset: v2}
          ____: 10

Show answer

        - destination: {host: api, subset: v2}
          weight: 10

Match.

DestinationRule

Subsets and policy
VirtualService

Routing rules
weight

Traffic share
outlierDetection

Circuit breaker

Next lesson: mTLS

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