Unavailable: last resolver error: produced zero addresses

azafoo · December 14, 2020, 10:25pm

Hi I observed several connection errors to my hosted slash.dgraph.io instance over the weekend:

I am using the dgraph-js lib from a node application.

Dec 12 04:08:27 PM 12-13-2020 00:08:27.360 [ERROR] 14 UNAVAILABLE: last connection error: connection error: desc = “transport: Error while dialing dial tcp 10.60.1.135:9080: i/o timeout”; last resolver error: produced zero addresses

Dec 13 08:13:04 PM 12-14-2020 04:13:04.039 [ERROR] 14 UNAVAILABLE: last connection error: connection error: desc = “transport: Error while dialing dial tcp 10.60.7.180:9080: connect: no route to host”; last resolver error: produced zero addresses

These appear to be server-generated grpc errors and I am wondering how to avoid these problems. In general, grpc unavailable errors may be handled with a retry, if applicable. I will go ahead and try to improve the resiliency of my app.

However, these do appear to be some kind of internal dns error. I am not familiar with how my instance is deployed, but I wonder if go - Handling "resolver returned no addresses" grpc error - Stack Overflow is related. Potential bug notwithstanding, is it expected that I should build in retry logic into my client-side code to handle this kind of error? Thanks for your time.

azafoo · December 14, 2020, 11:16pm

I notice this error is produced in grpc-go here:

github.com

grpc/grpc-go/blob/master/pickfirst.go#L67


			Picker: &picker{err: fmt.Errorf("name resolver error: %v", err)},
		})
	}
	if logger.V(2) {
		logger.Infof("pickfirstBalancer: ResolverError called with error %v", err)
	}
}

func (b *pickfirstBalancer) UpdateClientConnState(cs balancer.ClientConnState) error {
	if len(cs.ResolverState.Addresses) == 0 {
		b.ResolverError(errors.New("produced zero addresses"))
		return balancer.ErrBadResolverState
	}
	if b.sc == nil {
		var err error
		b.sc, err = b.cc.NewSubConn(cs.ResolverState.Addresses, balancer.NewSubConnOptions{})
		if err != nil {
			if logger.V(2) {
				logger.Errorf("pickfirstBalancer: failed to NewSubConn: %v", err)
			}
			b.state = connectivity.TransientFailure

Apologies if this sends someone down the wrong path, but it seems an interesting line of inquiry.

gja · December 15, 2020, 8:55am

Thanks for this report. WE’ll take a look and get back to you

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Unavailable: last resolver error: produced zero addresses

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