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grpclb: recover after receiving an empty server list #4879

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merged 3 commits into from Oct 20, 2021
Merged

grpclb: recover after receiving an empty server list #4879

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e4afd4f
[grpclb_empty_address] grpclb: recover after receiving an empty serve…
menghanl Oct 15, 2021
db2b3bc
[grpclb_empty_address] c1
menghanl Oct 19, 2021
73f3648
[grpclb_empty_address] c2
menghanl Oct 19, 2021
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12 changes: 10 additions & 2 deletions balancer/grpclb/grpclb_remote_balancer.go
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Expand Up @@ -135,11 +135,19 @@ func (lb *lbBalancer) refreshSubConns(backendAddrs []resolver.Address, fallback
}

if lb.usePickFirst {
var sc balancer.SubConn
for _, sc = range lb.subConns {
var (
scKey resolver.Address
sc balancer.SubConn
)
for scKey, sc = range lb.subConns {
break
}
if sc != nil {
if len(backendAddrs) == 0 {
lb.cc.cc.RemoveSubConn(sc)
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Is it better to handle this UpdateAddresses() so that every balancer need not handle this?

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Yes. That's what #4881 is tracking.

delete(lb.subConns, scKey)
return
}
lb.cc.cc.UpdateAddresses(sc, backendAddrs)
sc.Connect()
return
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72 changes: 72 additions & 0 deletions balancer/grpclb/grpclb_test.go
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Expand Up @@ -1274,6 +1274,78 @@ func (s) TestGRPCLBBackendConnectionErrorPropagation(t *testing.T) {
wg.Wait()
}

func testGRPCLBEmptyServerList(t *testing.T, svcfg string) {
r := manual.NewBuilderWithScheme("whatever")

tss, cleanup, err := startBackendsAndRemoteLoadBalancer(1, "", nil)
if err != nil {
t.Fatalf("failed to create new load balancer: %v", err)
}
defer cleanup()

beServers := []*lbpb.Server{{
IpAddress: tss.beIPs[0],
Port: int32(tss.bePorts[0]),
LoadBalanceToken: lbToken,
}}

creds := serverNameCheckCreds{}
ctx, cancel := context.WithTimeout(context.Background(), defaultTestTimeout)
defer cancel()
cc, err := grpc.DialContext(ctx, r.Scheme()+":///"+beServerName, grpc.WithResolvers(r),
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Minor nit: Could we not split these lines in a random way. In a recent PR, I cleaned up this test to instead do

	cc, err := grpc.Dial(r.Scheme()+":///"+beServerName,
		grpc.WithResolvers(r),
		grpc.WithTransportCredentials(&serverNameCheckCreds{}),
		grpc.WithContextDialer(fakeNameDialer))
	if err != nil {
		t.Fatalf("Failed to dial to the backend %v", err)
	}

which is a tad more readable I think.

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Done

grpc.WithTransportCredentials(&creds), grpc.WithContextDialer(fakeNameDialer))
if err != nil {
t.Fatalf("Failed to dial to the backend %v", err)
}
defer cc.Close()
testC := testpb.NewTestServiceClient(cc)

tss.ls.sls <- &lbpb.ServerList{Servers: beServers}

scpr := r.CC.ParseServiceConfig(svcfg)
if scpr.Err != nil {
t.Fatalf("Error parsing config %q: %v", svcfg, scpr.Err)
}

r.UpdateState(resolver.State{
Addresses: []resolver.Address{{
Addr: tss.lbAddr,
Type: resolver.GRPCLB,
ServerName: lbServerName,
}},
ServiceConfig: scpr,
})
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Nit: similarly I cleaned up calls to UpdateState to include balancer addresses through an attribute instead of the deprecated Type field.

	rs = grpclbstate.Set(resolver.State{ServiceConfig: r.CC.ParseServiceConfig(grpclbConfig)},
		&grpclbstate.State{BalancerAddresses: []resolver.Address{{
			Addr:       tss.lbAddr,
			ServerName: lbServerName,
		}}})
	r.UpdateState(rs)

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Done

t.Log("Perform an initial RPC and expect it to succeed...")
if _, err := testC.EmptyCall(ctx, &testpb.Empty{}, grpc.WaitForReady(true)); err != nil {
t.Fatalf("Initial _.EmptyCall(_, _) = _, %v, want _, <nil>", err)
}
t.Log("Now send an empty server list. Wait until we see an RPC failure to make sure the client got it...")
tss.ls.sls <- &lbpb.ServerList{}
gotError := false
for i := 0; i < 100; i++ {
if _, err := testC.EmptyCall(ctx, &testpb.Empty{}); err != nil {
gotError = true
break
}
}
if !gotError {
t.Fatalf("Expected to eventually see an RPC fail after the grpclb sends an empty server list, but none did.")
}
t.Log("Now send a non-empty server list. A wait-for-ready RPC should now succeed...")
tss.ls.sls <- &lbpb.ServerList{Servers: beServers}
if _, err := testC.EmptyCall(ctx, &testpb.Empty{}, grpc.WaitForReady(true)); err != nil {
t.Fatalf("Final _.EmptyCall(_, _) = _, %v, want _, <nil>", err)
}
}

func (s) TestGRPCLBEmptyServerListRoundRobin(t *testing.T) {
testGRPCLBEmptyServerList(t, `{"loadBalancingConfig":[{"grpclb":{"childPolicy":[{"round_robin":{}}]}}]}`)
}

func (s) TestGRPCLBEmptyServerListPickFirst(t *testing.T) {
testGRPCLBEmptyServerList(t, `{"loadBalancingConfig":[{"grpclb":{"childPolicy":[{"pick_first":{}}]}}]}`)
}

func (s) TestGRPCLBWithTargetNameFieldInConfig(t *testing.T) {
r := manual.NewBuilderWithScheme("whatever")

Expand Down