fix(gax-grpc): add pick_first fallback to direct path service config (#4143)

westarle · web-flow · commit 4934ad861407 · 2026-03-16T16:34:42.000-04:00
The `Dependency Compatibility Test` CI workflow has been failing on the `InstantiatingGrpcChannelProviderTest` tests (e.g. `canUseDirectPath_happyPath`) with the following error during initialization: `java.lang.IllegalStateException: Default config is invalid: Status{code=UNKNOWN, description=None of [grpclb] specified by Service Config are available., cause=null}` **Root Cause & DNS Spam Issue:** As of `grpc-java` v1.77.0, the `grpc-grpclb` artifact is no longer implicitly included because the legacy `grpclb` load balancer plugin is deprecated (Tracked in #4012). However, `InstantiatingGrpcChannelProvider` still hardcoded `grpclb` as its primary DirectPath load balancing policy. This missing plugin crashes tests, but the backend Google `grpclb` lookaside servers were also officially turned down in July 2025. Because the library still explicitly requests `grpclb`, it causes gRPC to continuously spam DNS with `_grpclb._tcp.*` SRV queries trying to find those dead servers. This leads to ~22,000 NXDOMAIN DNS errors a day on user networks (Tracked in googleapis/java-pubsub#2404). **Fix:** This PR completely removes `grpclb` and replaces it with `pick_first` in `getDefaultDirectPathServiceConfig()`. We deliberately choose `pick_first` to preserve the original 2019 design intent (maintaining exactly one connection per pooled GAX channel to emulate CFE behavior) and to provide a safe, fail-open default. While Traffic Director relies on the `xds` API, configuring it as a default fallback would require complex bootstrap configurations and cause crashes for clients without that setup. `pick_first` stops the DNS spam entirely, ensures stability on modern gRPC versions, and resolves the test failures.
diff --git a/sdk-platform-java/gax-java/gax-grpc/src/main/java/com/google/api/gax/grpc/InstantiatingGrpcChannelProvider.java b/sdk-platform-java/gax-java/gax-grpc/src/main/java/com/google/api/gax/grpc/InstantiatingGrpcChannelProvider.java
@@ -1434,7 +1434,7 @@ public ApiFunction<ManagedChannelBuilder, ManagedChannelBuilder> getChannelConfi
   }
 
   private static ImmutableMap<String, ?> getDefaultDirectPathServiceConfig() {
-    // When channel pooling is enabled, force the pick_first grpclb strategy.
+    // When channel pooling is enabled, force the pick_first strategy.
     // This is necessary to avoid the multiplicative effect of creating channel pool with
     // `poolSize` number of `ManagedChannel`s, each with a `subSetting` number of number of
     // subchannels.
@@ -1443,13 +1443,8 @@ public ApiFunction<ManagedChannelBuilder, ManagedChannelBuilder> getChannelConfi
     ImmutableMap<String, Object> pickFirstStrategy =
         ImmutableMap.<String, Object>of("pick_first", ImmutableMap.of());
 
-    ImmutableMap<String, Object> childPolicy =
-        ImmutableMap.<String, Object>of("childPolicy", ImmutableList.of(pickFirstStrategy));
-
-    ImmutableMap<String, Object> grpcLbPolicy =
-        ImmutableMap.<String, Object>of("grpclb", childPolicy);
-
-    return ImmutableMap.<String, Object>of("loadBalancingConfig", ImmutableList.of(grpcLbPolicy));
+    return ImmutableMap.<String, Object>of(
+        "loadBalancingConfig", ImmutableList.of(pickFirstStrategy));
   }
 
   private static void validateEndpoint(String endpoint) {
diff --git a/sdk-platform-java/gax-java/gax-grpc/src/test/java/com/google/api/gax/grpc/InstantiatingGrpcChannelProviderTest.java b/sdk-platform-java/gax-java/gax-grpc/src/test/java/com/google/api/gax/grpc/InstantiatingGrpcChannelProviderTest.java
@@ -235,7 +235,7 @@ void testToBuilder() {
         builder -> {
           throw new UnsupportedOperationException();
         };
-    Map<String, ?> directPathServiceConfig = ImmutableMap.of("loadbalancingConfig", "grpclb");
+    Map<String, ?> directPathServiceConfig = ImmutableMap.of("loadBalancingConfig", "pick_first");
     List<InstantiatingGrpcChannelProvider.HardBoundTokenTypes> hardBoundTokenTypes =
         new ArrayList<>();
     hardBoundTokenTypes.add(InstantiatingGrpcChannelProvider.HardBoundTokenTypes.ALTS);
@@ -549,11 +549,7 @@ void testWithDefaultDirectPathServiceConfig() {
     List<Map<String, ?>> lbConfigs = getAsObjectList(defaultServiceConfig, "loadBalancingConfig");
     assertThat(lbConfigs).hasSize(1);
     Map<String, ?> lbConfig = lbConfigs.get(0);
-    Map<String, ?> grpclb = getAsObject(lbConfig, "grpclb");
-    List<Map<String, ?>> childPolicies = getAsObjectList(grpclb, "childPolicy");
-    assertThat(childPolicies).hasSize(1);
-    Map<String, ?> childPolicy = childPolicies.get(0);
-    assertThat(childPolicy.keySet()).containsExactly("pick_first");
+    assertThat(lbConfig.keySet()).containsExactly("pick_first");
   }
 
   @Nullable
@@ -599,10 +595,10 @@ void testWithCustomDirectPathServiceConfig() {
     ImmutableMap<String, Object> childPolicy =
         ImmutableMap.<String, Object>of(
             "childPolicy", ImmutableList.of(pickFirstStrategy), "foo", "bar");
-    ImmutableMap<String, Object> grpcLbPolicy =
-        ImmutableMap.<String, Object>of("grpclb", childPolicy);
+    ImmutableMap<String, Object> customLbPolicy =
+        ImmutableMap.<String, Object>of("my_custom_lb", childPolicy);
     Map<String, Object> passedServiceConfig = new HashMap<>();
-    passedServiceConfig.put("loadBalancingConfig", ImmutableList.of(grpcLbPolicy));
+    passedServiceConfig.put("loadBalancingConfig", ImmutableList.of(customLbPolicy));
 
     InstantiatingGrpcChannelProvider provider =
         InstantiatingGrpcChannelProvider.newBuilder()
