Round Robin for gRPC (nodejs) on kubernetes with headless service

Question

I have a a 3 nodejs grpc server pods and a headless kubernetes service for the grpc service (returns all 3 pod ips with dns tested with getent hosts from within the pod). However all grpc client request always end up at a single server.

According to https://stackoverflow.com/a/39756233/2952128 (last paragraph) round robin per call should be possible Q1 2017. I am using grpc 1.1.2

I tried to give {"loadBalancingPolicy": "round-robin"} as options for new Client(address, credentials, options) and use dns:///service:port as address. If I understand documentation/code correctly this should be handed down to the c-core and use the newly implemented round robin channel creation. (https://github.com/grpc/grpc/blob/master/doc/service_config.md)

Is this how round-robin load balancer is supposed to work now? Is it already released with grpc 1.1.2?

Answer 1

After diving deep into Grpc-c core code and the nodejs adapter I found that it works by using the option key "grpc.lb_policy_name". Therefore, constructing the gRPC client with

new Client(address, credentials, {"grpc.lb_policy_name": "round_robin"})

works. Note that in my original question I also used round-robin instead of the correct round_robin

I am still not completely sure how to set the serviceConfig from the service side with nodejs instead of using client (channel) option override.

Answer 2

I'm not sure if this helps, but this discussion shows how to implement load balancing strategies via grpc.service_config.

const options = {
    'grpc.ssl_target_name_override': ...,
    'grpc.lb_policy_name': 'round_robin', // <--- has no effect in grpc-js
    'grpc.service_config': JSON.stringify({ loadBalancingConfig: [{ round_robin: {} }] }),  // <--- but this still works
};