Unable to get gRPC DNS resolver to return multiple IP addresses

[Gaurav Poothia]

Hello,

I am prototyping gRPC client side round robin load balancing.

So if client wants to dial to "localhost" I want it to load balance requests round robin over different loopback addresses e.g. 127.0.0.1, 127.0.0.2, 127.0.03 etc

For this experiment I configured unbound (by local DSN) to appropriately return multiple A records for "localhost" like so:

$ dig localhost

; <<>> DiG 9.16.1-Ubuntu <<>> localhost

;; global options: +cmd

;; Got answer:

;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 7826

;; flags: qr aa rd ra; QUERY: 1, ANSWER: 3, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:

; EDNS: version: 0, flags:; udp: 4096

;; QUESTION SECTION:

;localhost.                     IN      A

;; ANSWER SECTION:

localhost.              10800   IN      A       127.0.0.1

localhost.              3600    IN      A       127.0.0.3

localhost.              3600    IN      A       127.0.0.2

;; Query time: 0 msec

;; SERVER: 127.0.0.1#53(127.0.0.1)

;; WHEN: Thu May 13 23:51:33 UTC 2021

;; MSG SIZE  rcvd: 86

I modified the hello world client in the grpc quick start guide to use round robin LB and 

const (

  address     = "dns:///localhost:50051"

  defaultName = "world"

)

func main() {

  resolver.SetDefaultScheme("dns")

  // Set up a connection to the server.

  conn, err := grpc.Dial(address, grpc.WithInsecure(), grpc.WithBalancerName(roundrobin.Name))

  if err != nil {

    log.Fatalf("did not connect: %v", err)

  }

  defer conn.Close()

  c := pb.NewGreeterClient(conn)

When I run this  I notice that the DNS resolver is returning only 1 IP address instead  3 IPs hence there is nothing to load balance

INFO: 2021/05/14 00:04:01 [core] parsed scheme: "dns"

INFO: 2021/05/14 00:04:01 [core] ccResolverWrapper: sending update to cc: {[{127.0.0.2:50051  <nil> 0 <nil>}] <nil> <nil>}

INFO: 2021/05/14 00:04:01 [balancer] base.baseBalancer: got new ClientConn state:  {{[{127.0.0.2:50051  <nil> 0 <nil>}] <nil> <nil>} <nil>}

INFO: 2021/05/14 00:04:01 [core] Subchannel Connectivity change to CONNECTING

INFO: 2021/05/14 00:04:01 [balancer] base.baseBalancer: handle SubConn state change: 0xc000119d10, CONNECTING

INFO: 2021/05/14 00:04:01 [core] Subchannel picks a new address "127.0.0.2:50051" to connect

INFO: 2021/05/14 00:04:01 [core] Channel Connectivity change to CONNECTING

INFO: 2021/05/14 00:04:01 [core] Subchannel Connectivity change to READY

INFO: 2021/05/14 00:04:01 [balancer] base.baseBalancer: handle SubConn state change: 0xc000119d10, READY

INFO: 2021/05/14 00:04:01 [roundrobin] roundrobinPicker: newPicker called with info: {map[0xc000119d10:{{127.0.0.2:50051  <nil> 0 <nil>}}]}

INFO: 2021/05/14 00:04:01 [core] Channel Connectivity change to READY

Any pointers on why dig(or nslookup) and the gRPC DNS resolver would return different number of IPs for the same name?

Thanks in advance!

[Gaurav Poothia]

Not sure why this worked when I changed the hostname from "localhost" to something custom.

Nevermind I think I am unblocked now.

thanks!

--
You received this message because you are subscribed to a topic in the Google Groups "grpc.io" group.
To unsubscribe from this topic, visit https://groups.google.com/d/topic/grpc-io/jwvUuO0Ltjs/unsubscribe.
To unsubscribe from this group and all its topics, send an email to grpc-io+u...@googlegroups.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/grpc-io/f9a7af26-522c-47dc-87e3-c05482f65c7fn%40googlegroups.com.