grpc-go/examples/features/customloadbalancer

Custom Load Balancer

This example shows how to deploy a custom load balancer in a ClientConn.

Try it

go run server/main.go

go run client/main.go

Explanation

Two echo servers are serving on "localhost:20000" and "localhost:20001". They will include their serving address in the response. So the server on "localhost:20001" will reply to the RPC with this is examples/customloadbalancing (from localhost:20001).

A client is created, to connect to both of these servers (they get both server addresses from the name resolver in two separate endpoints). The client is configured with the load balancer specified in the service config, which in this case is custom_round_robin.

custom_round_robin

The client is configured to use custom_round_robin. custom_round_robin creates a pick first child for every endpoint it receives. It waits until both pick first children become ready, then defers to the first pick first child's picker, choosing the connection to localhost:20000, except every chooseSecond times, where it defers to second pick first child's picker, choosing the connection to localhost:20001 (or vice versa).

custom_round_robin is written as a delegating policy wrapping pick_first load balancers, one for every endpoint received. This is the intended way a user written custom lb should be specified, as pick first will contain a lot of useful functionality, such as Sticky Transient Failure, Happy Eyeballs, and Health Checking.

this is examples/customloadbalancing (from localhost:50050)
this is examples/customloadbalancing (from localhost:50050)
this is examples/customloadbalancing (from localhost:50051)
this is examples/customloadbalancing (from localhost:50050)
this is examples/customloadbalancing (from localhost:50050)
this is examples/customloadbalancing (from localhost:50051)
this is examples/customloadbalancing (from localhost:50050)
this is examples/customloadbalancing (from localhost:50050)
this is examples/customloadbalancing (from localhost:50051)