Istiod sends configuration to each sidecar using a long-lived gRPC stream. It has several characteristics that affect scaling:

• The size of the configuration to generate
  • Total number of services/pods & Istio resources
  • For large scale, adjust settings for the Sidecar to reduce the configuration size.
• The rate of change in the environment
  • When a new service is created or the Istio configuration is changed, full updates are sent to proxies.
  • Adding new endpoints is inexpensive for performance, because only incremental updates are sent.
• The number of proxies for which configuration is generated
  • Affected by the number of gateways and pods with a sidecar.

Scalability concerns

Approaches

1. Reduce APIServer calls
   1. eliminate unnecessary get & list
2. Processing time, less processing steps, optimize loops
3. Push to Envoy
   1. eliminate unnecessary push
   2. reduce config size