Load balancing

Policies

YARP ships with several built-in load balancing policies:

• Round robin — cycles through the destination list in order, giving each an equal share of traffic.
• Least requests — sends each request to whichever destination currently has the fewest in-flight requests.
• Random — picks a destination at random.
• Power of two choices — samples two random destinations and picks whichever has fewer in-flight requests, a good default at scale since it avoids the herd effect random selection alone can cause.
• First — always the first available destination; mainly useful for testing and A/B scenarios.

JSON{
  "Clusters": {
    "cluster1": {
      "LoadBalancingPolicy": "PowerOfTwoChoices",
      "Destinations": {
        "cluster1/destination1": { "Address": "https://localhost:10000/" },
        "cluster1/destination2": { "Address": "https://localhost:10010/" }
      }
    }
  }
}

Configuration

The default policy is Power of two choices when none is specified. Only destinations known to be healthy are considered - see Destination health checks for how a destination is marked unhealthy and excluded from rotation.

Custom policies

Implement ILoadBalancingPolicy and register it in DI to plug in custom selection logic - the same extensibility point YARP's own built-in policies are built on.