example of how we could route traffic by header

proxysql-example.yaml

# There's an assumption here that there are multiple Services defined
# for ProxySQL, each with a label of `cluster`. Each Service points to
# its own Deployment, which handles requests for that cluster
---
apiVersion: networking.istio.io/v1alpha3
kind: DestinationRule
metadata:
  name: reviews
spec:
  host: proxysql
  subsets:
  - { name: cluster-100, labels: { cluster: "100" } }
  - { name: cluster-101, labels: { cluster: "101" } }
  - { name: cluster-102, labels: { cluster: "102" } }
---
apiVersion: networking.istio.io/v1alpha3
kind: VirtualService
metadata:
  name: proxysql-cluster
spec:
  hosts:
    - proxysql-header
  http:
  # Cluster-100
  - match:
      - headers: { X-Zendesk-Cluster-Id: { exact: "100" } }
    route:
      - destination: { host: proxysql, subset: cluster-100 }
  # Cluster-101
  - match:
      - headers: { X-Zendesk-Cluster-Id: { exact: "101" } }
    route:
      - destination: { host: proxysql, subset: cluster-101 }
  ### Default route
  - route:
    - destination: { host: proxysql, subset: cluster-100 }