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Distributed Services with Go: accessing the service outside the pods (Beta-4 pg.223)

csrfr

csrfr

Distributed Services with Go: accessing the service outside the pods (Beta-4 pg.223)

Once deployed, I am not able to access the service outside the prolog pods. I can run the client successfully and access the service from a client running on one of the proglog pods.

However, I am not able to access the service from the following locations:

  1. Laptop: The client connection hangs and then returns connection error while dialing dial tcp: lookup proglog-0.proglog.mysvcs.svc.cluster.local: no such host. I am dialing using the EXTERNAL-IP address of proglog-0 from k8s in the client (This address works when used from a proglog pod).

  2. From a pod in the k8s cluster but not a proglog pod. It prints the following error repeatedly ERROR: 2020/10/31 18:59:29 [core] subconn returned from pick is not *acBalancerWrapper. Also, the acBalancerWrapper error appears when running the client from a proglog pod (where it usually works) from time to time.

Anyone faced this before, ideas?
At the moment I’m looking into GetServers returning the K8s DNS names (e.g. proglog-0.proglog.default.svc.cluster.local:8400 rather than the EXTERNAL-IP of the pods.

5 comments
#question/book-distributed-services-with-go
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Marked As Solved

travisjeffery

travisjeffery

Author of Distributed Services with Go

Yeah we should return ErrNoSubConnAvailable like so:

func (p *Picker) Pick(info balancer.PickInfo) (
	balancer.PickResult, error) {
	p.mu.RLock()
	defer p.mu.RUnlock()
	var result balancer.PickResult
	if strings.Contains(info.FullMethodName, "Produce") ||
		len(p.followers) == 0 {
		result.SubConn = p.leader
	} else if strings.Contains(info.FullMethodName, "Consume") {
		result.SubConn = p.nextFollower()
	}
	if result.SubConn == nil {
		return result, balancer.ErrNoSubConnAvailable
	}
	return result, nil
}

so gRPC will block the RPC until a new picker is available with available sub connections.

2
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Also Liked

travisjeffery

travisjeffery

Author of Distributed Services with Go

For 1. did you port-forward the pod/service to expose it outside k8s’ network? That’s what the $ kubectl port-forward pod/proglog-0 8400 8400 command in the book is for.

  1. Could be because leader election is still underway so a nil subconn is returned for it.
1
Post #2
travisjeffery

travisjeffery

Author of Distributed Services with Go

For 2. I think the error handling should be improved. I’m looking into it.

1
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