This page provides an overview of how traffic management works in Istio, including the benefits of its traffic management principles. It assumes that you've already read What Is Istio? and are familiar with Istio's high-level architecture. You can find out more about individual traffic management features in the other guides in this section.
Pilot and Envoy
The core component used for traffic management in Istio is Pilot, which manages and configures all the Envoy proxy instances deployed in a particular Istio service mesh. It lets you specify what rules you want to use to route traffic between Envoy proxies and configure failure recovery features such as timeouts, retries, and circuit breakers. It also maintains a canonical model of all the services in the mesh and uses this to let Envoys know about the other instances in the mesh via its discovery service.
Each Envoy instance maintains load balancing information based on the information it gets from Pilot and periodic health-checks of other instances in its load-balancing pool, allowing it to intelligently distribute traffic between destination instances while following its specified routing rules.
Traffic management benefits
Using Istio's traffic management model essentially decouples traffic flow and infrastructure scaling, letting operators specify via Pilot what rules they want traffic to follow rather than which specific pods/VMs should receive traffic - Pilot and intelligent Envoy proxies look after the rest. So, for example, you can specify via Pilot that you want 5% of traffic for a particular service to go to a canary version irrespective of the size of the canary deployment, or send traffic to a particular version depending on the content of the request.
Decoupling traffic flow from infrastructure scaling like this allows Istio to provide a variety of traffic management features that live outside the application code. As well as dynamic request routing for A/B testing, gradual rollouts, and canary releases, it also handles failure recovery using timeouts, retries, and circuit breakers, and finally fault injection to test the compatibility of failure recovery policies across services. These capabilities are all realized through the Envoy sidecars/proxies deployed across the service mesh.