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grpclb: keep RR Subchannel state in TRANSIENT_FAILURE until becoming READY #7816

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Jan 15, 2021
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grpclb: keep RR Subchannel state in TRANSIENT_FAILURE until becoming READY #7816

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17 changes: 14 additions & 3 deletions grpclb/src/main/java/io/grpc/grpclb/GrpclbState.java
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Original file line number Diff line number Diff line change
Expand Up @@ -203,9 +203,20 @@ void handleSubchannelState(Subchannel subchannel, ConnectivityStateInfo newState
if (config.getMode() == Mode.ROUND_ROBIN && newState.getState() == IDLE) {
subchannel.requestConnection();
}
subchannel.getAttributes().get(STATE_INFO).set(newState);
maybeUseFallbackBackends();
maybeUpdatePicker();
AtomicReference<ConnectivityStateInfo> stateInfoRef =
subchannel.getAttributes().get(STATE_INFO);
// If all RR servers are unhealthy, it's possible that at least one connection is CONNECTING at
// every moment which causes RR to stay in CONNECTING. It's better to keep the TRANSIENT_FAILURE
// state in that case so that fail-fast RPCs can fail fast.
boolean keepState =
config.getMode() == Mode.ROUND_ROBIN
&& stateInfoRef.get().getState() == TRANSIENT_FAILURE
&& (newState.getState() == CONNECTING || newState.getState() == IDLE);
if (!keepState) {
stateInfoRef.set(newState);
maybeUseFallbackBackends();
maybeUpdatePicker();
}
}

/**
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43 changes: 43 additions & 0 deletions grpclb/src/test/java/io/grpc/grpclb/GrpclbLoadBalancerTest.java
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Original file line number Diff line number Diff line change
Expand Up @@ -1104,6 +1104,49 @@ public void grpclbWorking() {
verify(subchannelPool).clear();
}

@Test
public void roundRobinMode_subchannelStayTransientFailureUntilReady() {
InOrder inOrder = inOrder(helper);
List<EquivalentAddressGroup> grpclbBalancerList = createResolvedBalancerAddresses(1);
deliverResolvedAddresses(Collections.<EquivalentAddressGroup>emptyList(), grpclbBalancerList);
verify(mockLbService).balanceLoad(lbResponseObserverCaptor.capture());
StreamObserver<LoadBalanceResponse> lbResponseObserver = lbResponseObserverCaptor.getValue();

// Simulate receiving LB response
List<ServerEntry> backends1 = Arrays.asList(
new ServerEntry("127.0.0.1", 2000, "token0001"),
new ServerEntry("127.0.0.1", 2010, "token0002"));
lbResponseObserver.onNext(buildInitialResponse());
lbResponseObserver.onNext(buildLbResponse(backends1));
assertEquals(2, mockSubchannels.size());
Subchannel subchannel1 = mockSubchannels.poll();
Subchannel subchannel2 = mockSubchannels.poll();

deliverSubchannelState(subchannel1, ConnectivityStateInfo.forNonError(CONNECTING));
deliverSubchannelState(subchannel2, ConnectivityStateInfo.forNonError(CONNECTING));
inOrder.verify(helper).updateBalancingState(eq(CONNECTING), any(SubchannelPicker.class));

// Switch subchannel1 to TRANSIENT_FAILURE, making the general state TRANSIENT_FAILURE too.
Status error = Status.UNAVAILABLE.withDescription("error1");
deliverSubchannelState(subchannel1, ConnectivityStateInfo.forTransientFailure(error));
inOrder.verify(helper).updateBalancingState(eq(TRANSIENT_FAILURE), pickerCaptor.capture());
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@voidzcy voidzcy Mar 11, 2021 •
edited
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This test is weird. subchannel2 is still connecting, so the overall state should be CONNECTING. This is mostly because subchannels with CONNECTING state are ignored when aggregating the overall state.

So, observing TRANSIENT_FAILURE isn't related to your change. And I believe that should be fixed. However, for this test case specifically, you should bring all subchannels into TRANSIENT_FAILURE and then perform the test for behaviors related to your change.

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It looks like we should stop ignoring CONNECTING with this change (and use the same logic as RR and elsewhere)

assertThat(((RoundRobinPicker) pickerCaptor.getValue()).pickList)
.containsExactly(new ErrorEntry(error));

// Switch subchannel1 to IDLE, then to CONNECTING, which are ignored since the previous
// subchannel state is TRANSIENT_FAILURE. General state is unchanged.
deliverSubchannelState(subchannel1, ConnectivityStateInfo.forNonError(IDLE));
deliverSubchannelState(subchannel1, ConnectivityStateInfo.forNonError(CONNECTING));
inOrder.verifyNoMoreInteractions();

// Switch subchannel1 to READY, which will affect the general state
deliverSubchannelState(subchannel1, ConnectivityStateInfo.forNonError(READY));
inOrder.verify(helper).updateBalancingState(eq(READY), pickerCaptor.capture());
assertThat(((RoundRobinPicker) pickerCaptor.getValue()).pickList)
.containsExactly(new BackendEntry(subchannel1, getLoadRecorder(), "token0001"));
inOrder.verifyNoMoreInteractions();
}

@Test
public void grpclbFallback_initialTimeout_serverListReceivedBeforeTimerExpires() {
subtestGrpclbFallbackInitialTimeout(false);
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