subsetting java impl

api/src/test/java/io/grpc/LoadBalancerRegistryTest.java

@@ -41,7 +41,7 @@ public void getClassesViaHardcoded_classesPresent() throws Exception {
   @Test
   public void stockProviders() {
     LoadBalancerRegistry defaultRegistry = LoadBalancerRegistry.getDefaultRegistry();
-    assertThat(defaultRegistry.providers()).hasSize(4);
+    assertThat(defaultRegistry.providers()).hasSize(5);
 
     LoadBalancerProvider pickFirst = defaultRegistry.getProvider("pick_first");
     assertThat(pickFirst).isInstanceOf(PickFirstLoadBalancerProvider.class);
@@ -56,7 +56,13 @@ public void stockProviders() {
         "outlier_detection_experimental");
     assertThat(outlierDetection.getClass().getName()).isEqualTo(
         "io.grpc.util.OutlierDetectionLoadBalancerProvider");
-    assertThat(roundRobin.getPriority()).isEqualTo(5);
+    assertThat(outlierDetection.getPriority()).isEqualTo(5);
+
+    LoadBalancerProvider deterministicSubsetting = defaultRegistry.getProvider(
+        "deterministic_subsetting");
+    assertThat(deterministicSubsetting.getClass().getName()).isEqualTo(
+        "io.grpc.util.DeterministicSubsettingLoadBalancerProvider");
+    assertThat(deterministicSubsetting.getPriority()).isEqualTo(5);
 
     LoadBalancerProvider grpclb = defaultRegistry.getProvider("grpclb");
     assertThat(grpclb).isInstanceOf(GrpclbLoadBalancerProvider.class);

util/src/main/java/io/grpc/util/DeterministicSubsettingLoadBalancer.java

@@ -0,0 +1,210 @@
+/*
+ * Copyright 2023 The gRPC Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package io.grpc.util;
+
+import static com.google.common.base.Preconditions.checkArgument;
+import static com.google.common.base.Preconditions.checkNotNull;
+import static com.google.common.base.Preconditions.checkState;
+
+import com.google.common.annotations.VisibleForTesting;
+import io.grpc.EquivalentAddressGroup;
+import io.grpc.Internal;
+import io.grpc.LoadBalancer;
+import io.grpc.Status;
+import io.grpc.internal.ServiceConfigUtil.PolicySelection;
+import java.net.SocketAddress;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.Comparator;
+import java.util.List;
+import java.util.Random;
+
+/**
+ * Wraps a child {@code LoadBalancer}, separating the total set of backends into smaller subsets for
+ * the child balancer to balance across.
+ *
+ * <p>This implements deterministic subsetting gRFC:
+ * https://github.com/grpc/proposal/blob/master/A68-deterministic-subsetting-lb-policy.md
+ */
+@Internal
+public final class DeterministicSubsettingLoadBalancer extends LoadBalancer {
+
+  private final GracefulSwitchLoadBalancer switchLb;
+
+  @Override
+  public boolean acceptResolvedAddresses(ResolvedAddresses resolvedAddresses) {
+    DeterministicSubsettingLoadBalancerConfig config =
+        (DeterministicSubsettingLoadBalancerConfig)
+            resolvedAddresses.getLoadBalancingPolicyConfig();
+
+    switchLb.switchTo(config.childPolicy.getProvider());
+
+    ResolvedAddresses subsetAddresses = buildSubsets(resolvedAddresses, config);
+
+    switchLb.handleResolvedAddresses(
+        subsetAddresses.toBuilder()
+            .setLoadBalancingPolicyConfig(config.childPolicy.getConfig())
+            .build());
+    return true;
+  }
+
+  // implements the subsetting algorithm, as described in A68:
+  // https://github.com/grpc/proposal/pull/383
+  private ResolvedAddresses buildSubsets(
+      ResolvedAddresses allAddresses, DeterministicSubsettingLoadBalancerConfig config) {
+    // The map should only retain entries for addresses in this latest update.
+    ArrayList<SocketAddress> addresses = new ArrayList<>();
+    for (EquivalentAddressGroup addressGroup : allAddresses.getAddresses()) {
+      addresses.addAll(addressGroup.getAddresses());
+    }
+
+    if (addresses.size() <= config.subsetSize) {
+      return allAddresses;
+    }
+    if (config.sortAddresses) {
+      // If we sort, we do so via the string representation of the SocketAddress.
+      addresses.sort(new AddressComparator());
+    }
+
+    Integer backendCount = addresses.size();
+    Integer subsetCount = backendCount / config.subsetSize;
+
+    Integer round = config.clientIndex / subsetCount;
+
+    Integer excludedCount = backendCount % config.subsetSize;
+    Integer excludedStart = (round * excludedCount) % backendCount;
+    Integer excludedEnd = (excludedStart + excludedCount) % backendCount;
+    if (excludedStart <= excludedEnd) {
+      List<SocketAddress> subList = addresses.subList(0, excludedStart);
+      subList.addAll(addresses.subList(excludedEnd, backendCount));
+      addresses = new ArrayList<>(subList);
+    } else {
+      addresses = new ArrayList<>(addresses.subList(excludedEnd, excludedStart));
+    }
+
+    Random r = new Random(round);
+    Collections.shuffle(addresses, r);
+
+    Integer subsetId = config.clientIndex % subsetCount;
+
+    Integer start = subsetId * config.subsetSize;
+    Integer end = start + config.subsetSize;
+
+    List<SocketAddress> subset = addresses.subList(start, end);
+
+    ArrayList<EquivalentAddressGroup> eaglist = new ArrayList<>();
+
+    // Create new EAGs per address
+    for (SocketAddress addr : subset) {
+      eaglist.add(new EquivalentAddressGroup(addr));
+    }
+
+    ResolvedAddresses.Builder builder = allAddresses.toBuilder();
+    return builder.setAddresses(eaglist).build();
+  }
+
+  @Override
+  public void handleNameResolutionError(Status error) {
+    switchLb.handleNameResolutionError(error);
+  }
+
+  @Override
+  public void shutdown() {
+    switchLb.shutdown();
+  }
+
+  public DeterministicSubsettingLoadBalancer(Helper helper) {
+    switchLb = new GracefulSwitchLoadBalancer(checkNotNull(helper, "helper"));
+  }
+
+  @VisibleForTesting
+  static class AddressComparator implements Comparator<SocketAddress> {
+    // For consistency with the golang instrumentation, this assumes toString is overridden such
+    // that it is a string representation of an IP. Though any string representation of a
+    // SocketAddress will work here, other definitions of toString may yield differing results from
+    // the golang instrumentation.
+    @Override
+    public int compare(SocketAddress o1, SocketAddress o2) {
+      return o1.toString().compareTo(o2.toString());
+    }
+  }
+
+  public static final class DeterministicSubsettingLoadBalancerConfig {
+
+    public final Integer clientIndex;
+    public final Integer subsetSize;
+    public final Boolean sortAddresses;
+
+    public final PolicySelection childPolicy;
+
+    private DeterministicSubsettingLoadBalancerConfig(
+        Integer clientIndex,
+        Integer subsetSize,
+        Boolean sortAddresses,
+        PolicySelection childPolicy) {
+      this.clientIndex = clientIndex;
+      this.subsetSize = subsetSize;
+      this.sortAddresses = sortAddresses;
+      this.childPolicy = childPolicy;
+    }
+
+    public static class Builder {
+      Integer clientIndex;
+      Integer subsetSize = 10;
+
+      Boolean sortAddresses;
+      PolicySelection childPolicy;
+
+      public Builder setClientIndex(Integer clientIndex) {
+        checkState(clientIndex != null);
+        // Indices must be positive integers.
+        checkState(clientIndex >= 0);
+        this.clientIndex = clientIndex;
+        return this;
+      }
+
+      public Builder setSubsetSize(Integer subsetSize) {
+        checkArgument(subsetSize != null);
+        // subsetSize of 1 is equivalent to `pick_first`. Use that policy if that behavior is
+        // desired.
+        // Fallback to default of 10 of condition is not satisfied.
+        checkArgument(subsetSize > 1);
+        this.subsetSize = subsetSize;
+        return this;
+      }
+
+      public Builder setSortAddresses(Boolean sortAddresses) {
+        checkArgument(sortAddresses != null);
+        this.sortAddresses = sortAddresses;
+        return this;
+      }
+
+      public Builder setChildPolicy(PolicySelection childPolicy) {
+        checkState(childPolicy != null);
+        this.childPolicy = childPolicy;
+        return this;
+      }
+
+      public DeterministicSubsettingLoadBalancerConfig build() {
+        checkState(childPolicy != null);
+        checkState(clientIndex != null);
+        return new DeterministicSubsettingLoadBalancerConfig(
+            clientIndex, subsetSize, sortAddresses, childPolicy);
+      }
+    }
+  }
+}

util/src/main/java/io/grpc/util/DeterministicSubsettingLoadBalancerProvider.java

@@ -0,0 +1,108 @@
+/*
+ * Copyright 2023 The gRPC Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package io.grpc.util;
+
+import io.grpc.Internal;
+import io.grpc.LoadBalancer;
+import io.grpc.LoadBalancerProvider;
+import io.grpc.LoadBalancerRegistry;
+import io.grpc.NameResolver.ConfigOrError;
+import io.grpc.Status;
+import io.grpc.internal.JsonUtil;
+import io.grpc.internal.ServiceConfigUtil;
+import io.grpc.internal.ServiceConfigUtil.PolicySelection;
+import java.util.List;
+import java.util.Map;
+
+@Internal
+public final class DeterministicSubsettingLoadBalancerProvider extends LoadBalancerProvider {
+
+  @Override
+  public LoadBalancer newLoadBalancer(LoadBalancer.Helper helper) {
+    return new DeterministicSubsettingLoadBalancer(helper);
+  }
+
+  @Override
+  public boolean isAvailable() {
+    return true;
+  }
+
+  @Override
+  public int getPriority() {
+    return 5;
+  }
+
+  @Override
+  public String getPolicyName() {
+    return "deterministic_subsetting";
+  }
+
+  @Override
+  public ConfigOrError parseLoadBalancingPolicyConfig(Map<String, ?> rawConfig) {
+    try {
+      return parseLoadBalancingPolicyConfigInternal(rawConfig);
+    } catch (RuntimeException e) {
+      return ConfigOrError.fromError(
+          Status.UNAVAILABLE
+              .withCause(e)
+              .withDescription("Failed parsing configuration for " + getPolicyName()));
+    }
+  }
+
+  private ConfigOrError parseLoadBalancingPolicyConfigInternal(Map<String, ?> rawConfig) {
+    Integer clientIndex = JsonUtil.getNumberAsInteger(rawConfig, "clientIndex");
+    Integer subsetSize = JsonUtil.getNumberAsInteger(rawConfig, "subsetSize");
+    Boolean sortAddresses = JsonUtil.getBoolean(rawConfig, "sortAddresses");
+
+    List<ServiceConfigUtil.LbConfig> childConfigCandidates =
+        ServiceConfigUtil.unwrapLoadBalancingConfigList(
+            JsonUtil.getListOfObjects(rawConfig, "childPolicy"));
+    if (childConfigCandidates == null || childConfigCandidates.isEmpty()) {
+      return ConfigOrError.fromError(
+          Status.INTERNAL.withDescription(
+              "No child policy in deterministic_subsetting LB policy " + rawConfig));
+    }
+
+    ConfigOrError selectedConfig =
+        ServiceConfigUtil.selectLbPolicyFromList(
+            childConfigCandidates, LoadBalancerRegistry.getDefaultRegistry());
+
+    DeterministicSubsettingLoadBalancer.DeterministicSubsettingLoadBalancerConfig.Builder
+        configBuilder =
+            new DeterministicSubsettingLoadBalancer.DeterministicSubsettingLoadBalancerConfig
+                .Builder();
+
+    configBuilder.setChildPolicy((PolicySelection) selectedConfig.getConfig());
+
+    if (clientIndex != null) {
+      configBuilder.setClientIndex(clientIndex);
+    } else {
+      return ConfigOrError.fromError(
+          Status.INTERNAL.withDescription(
+              "No client index set, cannot determine subsets " + rawConfig));
+    }
+
+    if (subsetSize != null) {
+      configBuilder.setSubsetSize(subsetSize);
+    }
+
+    if (sortAddresses != null) {
+      configBuilder.setSortAddresses(sortAddresses);
+    }
+    return ConfigOrError.fromConfig(configBuilder.build());
+  }
+}

util/src/main/resources/META-INF/services/io.grpc.LoadBalancerProvider

@@ -1,2 +1,3 @@
 io.grpc.util.SecretRoundRobinLoadBalancerProvider$Provider
 io.grpc.util.OutlierDetectionLoadBalancerProvider
+io.grpc.util.DeterministicSubsettingLoadBalancerProvider