Merge pull request #1449 from murgatroid99/grpc-js_weighted_target_lb

grpc-js: Add weighted_target load balancer

Author: murgatroid99

packages/grpc-js/src/load-balancer-weighted-target.ts

@@ -0,0 +1,322 @@
+/*
+ * Copyright 2020 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.
+ *
+ */
+
+import { LoadBalancer, ChannelControlHelper, getFirstUsableConfig, registerLoadBalancerType } from "./load-balancer";
+import { SubchannelAddress } from "./subchannel";
+import { LoadBalancingConfig, WeightedTarget, isWeightedTargetLoadBalancingConfig } from "./load-balancing-config";
+import { Picker, PickResult, PickArgs, QueuePicker, UnavailablePicker } from "./picker";
+import { ConnectivityState } from "./channel";
+import { ChildLoadBalancerHandler } from "./load-balancer-child-handler";
+import { Status } from "./constants";
+import { Metadata } from "./metadata";
+import { isLocalitySubchannelAddress, LocalitySubchannelAddress } from "./load-balancer-priority";
+
+const TYPE_NAME = 'weighted_target';
+
+const DEFAULT_RETENTION_INTERVAL_MS = 15 * 60 * 1000;
+
+/**
+ * Represents a picker and a subinterval of a larger interval used for randomly
+ * selecting an element of a list of these objects.
+ */
+interface WeightedPicker {
+  picker: Picker;
+  /**
+   * The exclusive end of the interval associated with this element. The start
+   * of the interval is implicitly the rangeEnd of the previous element in the
+   * list, or 0 for the first element in the list.
+   */
+  rangeEnd: number;
+}
+
+class WeightedTargetPicker implements Picker {
+  private rangeTotal: number;
+  constructor(private readonly pickerList: WeightedPicker[]) {
+    this.rangeTotal = pickerList[pickerList.length - 1].rangeEnd;
+  }
+  pick(pickArgs: PickArgs): PickResult {
+    // num | 0 is equivalent to floor(num)
+    const selection = (Math.random() * this.rangeTotal) | 0;
+    
+    /* Binary search for the element of the list such that
+     * pickerList[index - 1].rangeEnd <= selection < pickerList[index].rangeEnd
+     */
+    let mid = 0;
+    let startIndex = 0;
+    let endIndex = this.pickerList.length - 1;
+    let index = 0;
+    while (endIndex > startIndex) {
+      mid = ((startIndex + endIndex) / 2) | 0;
+      if (this.pickerList[mid].rangeEnd > selection) {
+        endIndex = mid;
+      } else if (this.pickerList[mid].rangeEnd < selection) {
+        startIndex = mid + 1;
+      } else {
+        // + 1 here because the range is exclusive at the top end
+        index = mid + 1;
+        break;
+      }
+    }
+    if (index === 0) {
+      index = startIndex;
+    }
+
+    return this.pickerList[index].picker.pick(pickArgs);
+  }
+}
+
+interface WeightedChild {
+  updateAddressList(addressList: SubchannelAddress[], lbConfig: WeightedTarget, attributes: { [key: string]: unknown; }): void;
+  exitIdle(): void;
+  resetBackoff(): void;
+  destroy(): void;
+  deactivate(): void;
+  maybeReactivate(): void;
+  getConnectivityState(): ConnectivityState;
+  getPicker(): Picker;
+  getWeight(): number;
+}
+
+export class WeightedTargetLoadBalancer implements LoadBalancer {
+  private WeightedChildImpl = class implements WeightedChild {
+    private connectivityState: ConnectivityState = ConnectivityState.IDLE;
+    private picker: Picker;
+    private childBalancer: ChildLoadBalancerHandler;
+    private deactivationTimer: NodeJS.Timer | null = null;
+    private weight: number = 0;
+
+    constructor(private parent: WeightedTargetLoadBalancer, private name: string) {
+      this.childBalancer = new ChildLoadBalancerHandler({
+        createSubchannel: (subchannelAddress, subchannelOptions) => {
+          return this.parent.channelControlHelper.createSubchannel(subchannelAddress, subchannelOptions);
+        },
+        updateState: (connectivityState, picker) => {
+          this.updateState(connectivityState, picker);
+        },
+        requestReresolution: () => {
+          this.parent.channelControlHelper.requestReresolution();
+        }
+      });
+
+      this.picker = new QueuePicker(this.childBalancer);
+    }
+
+    private updateState(connectivityState: ConnectivityState, picker: Picker) {
+      this.connectivityState = connectivityState;
+      this.picker = picker;
+      this.parent.updateState();
+    }
+
+    updateAddressList(addressList: SubchannelAddress[], lbConfig: WeightedTarget, attributes: { [key: string]: unknown; }): void {
+      this.weight = lbConfig.weight;
+      const childConfig = getFirstUsableConfig(lbConfig.child_policy);
+      if (childConfig !== null) {
+        this.childBalancer.updateAddressList(addressList, childConfig, attributes);
+      }
+    }
+    exitIdle(): void {
+      this.childBalancer.exitIdle();
+    }
+    resetBackoff(): void {
+      this.childBalancer.resetBackoff();
+    }
+    destroy(): void {
+      this.childBalancer.destroy();
+      if (this.deactivationTimer !== null) {
+        clearTimeout(this.deactivationTimer);
+      }
+    }
+    deactivate(): void {
+      if (this.deactivationTimer === null) {
+        this.deactivationTimer = setTimeout(() => {
+          this.parent.targets.delete(this.name);
+          this.deactivationTimer = null;
+        }, DEFAULT_RETENTION_INTERVAL_MS);
+      }
+    }
+    maybeReactivate(): void {
+      if (this.deactivationTimer !== null) {
+        clearTimeout(this.deactivationTimer);
+        this.deactivationTimer = null;
+      }
+    }
+    getConnectivityState(): ConnectivityState {
+      return this.connectivityState;
+    }
+    getPicker(): Picker {
+      return this.picker;
+    }
+    getWeight(): number {
+      return this.weight;
+    }
+  }
+  // end of WeightedChildImpl
+
+  /**
+   * Map of target names to target children. Includes current targets and
+   * previous targets with deactivation timers that have not yet triggered.
+   */
+  private targets: Map<string, WeightedChild> = new Map<string, WeightedChild>();
+  /**
+   * List of current target names.
+   */
+  private targetList: string[] = [];
+
+  constructor(private channelControlHelper: ChannelControlHelper) {}
+
+  private updateState() {
+    const pickerList: WeightedPicker[] = [];
+    let end = 0;
+
+    let connectingCount = 0;
+    let idleCount = 0;
+    let transientFailureCount = 0;
+    for (const targetName of this.targetList) {
+      const target = this.targets.get(targetName);
+      if (target === undefined) {
+        continue;
+      }
+      switch (target.getConnectivityState()) {
+        case ConnectivityState.READY:
+          end += target.getWeight();
+          pickerList.push({
+            picker: target.getPicker(),
+            rangeEnd: end
+          });
+          break;
+        case ConnectivityState.CONNECTING:
+          connectingCount += 1;
+          break;
+        case ConnectivityState.IDLE:
+          idleCount += 1;
+          break;
+        case ConnectivityState.TRANSIENT_FAILURE:
+          transientFailureCount += 1;
+          break;
+        default:
+          // Ignore the other possiblity, SHUTDOWN
+      }
+    }
+
+    let connectivityState: ConnectivityState;
+    if (pickerList.length > 0) {
+      connectivityState = ConnectivityState.READY;
+    } else if (connectingCount > 0) {
+      connectivityState = ConnectivityState.CONNECTING;
+    } else if (idleCount > 0) {
+      connectivityState = ConnectivityState.IDLE;
+    } else {
+      connectivityState = ConnectivityState.TRANSIENT_FAILURE;
+    }
+
+    let picker: Picker;
+    switch (connectivityState) {
+      case ConnectivityState.READY:
+        picker = new WeightedTargetPicker(pickerList);
+        break;
+      case ConnectivityState.CONNECTING:
+      case ConnectivityState.READY:
+        picker = new QueuePicker(this);
+        break;
+      default:
+        picker = new UnavailablePicker({
+          code: Status.UNAVAILABLE,
+          details: 'weighted_target: all children report state TRANSIENT_FAILURE',
+          metadata: new Metadata()
+        });
+    }
+    this.channelControlHelper.updateState(connectivityState, picker);
+  }
+
+  updateAddressList(addressList: SubchannelAddress[], lbConfig: LoadBalancingConfig, attributes: { [key: string]: unknown; }): void {
+    if (!isWeightedTargetLoadBalancingConfig(lbConfig)) {
+      // Reject a config of the wrong type
+      return;
+    }
+
+    /* For each address, the first element of its localityPath array determines
+     * which child it belongs to. So we bucket those addresses by that first
+     * element, and pass along the rest of the localityPath for that child
+     * to use. */
+    const childAddressMap = new Map<string, SubchannelAddress[]>();
+    for (const address of addressList) {
+      if (!isLocalitySubchannelAddress(address)) {
+        // Reject address that cannot be associated with targets
+        return;
+      }
+      if (address.localityPath.length < 1) {
+        // Reject address that cannot be associated with targets
+        return;
+      }
+      const childName = address.localityPath[0];
+      const childAddress: LocalitySubchannelAddress = {
+        ...address,
+        localityPath: address.localityPath.slice(1),
+      };
+      let childAddressList = childAddressMap.get(childName);
+      if (childAddressList === undefined) {
+        childAddressList = [];
+        childAddressMap.set(childName, childAddressList);
+      }
+      childAddressList.push(childAddress);
+    }
+
+    this.targetList = Array.from(lbConfig.weighted_target.targets.keys());
+    for (const [targetName, targetConfig] of lbConfig.weighted_target.targets) {
+      let target = this.targets.get(targetName);
+      if (target === undefined) {
+        target = new this.WeightedChildImpl(this, targetName);
+        this.targets.set(targetName, target);
+      } else {
+        target.maybeReactivate();
+      }
+      target.updateAddressList(childAddressMap.get(targetName) ?? [], targetConfig, attributes);
+    }
+
+    // Deactivate targets that are not in the new config
+    for (const [targetName, target] of this.targets) {
+      if (this.targetList.indexOf(targetName) < 0) {
+        target.deactivate();
+      }
+    }
+
+    this.updateState();
+  }
+  exitIdle(): void {
+    for (const targetName of this.targetList) {
+      this.targets.get(targetName)?.exitIdle();
+    }
+  }
+  resetBackoff(): void {
+    for (const targetName of this.targetList) {
+      this.targets.get(targetName)?.resetBackoff();
+    }
+  }
+  destroy(): void {
+    for (const target of this.targets.values()) {
+      target.destroy();
+    }
+    this.targets.clear();
+  }
+  getTypeName(): string {
+    return TYPE_NAME;
+  }
+}
+
+export function setup() {
+  registerLoadBalancerType(TYPE_NAME, WeightedTargetLoadBalancer);
+}

packages/grpc-js/src/load-balancer.ts

@@ -23,6 +23,7 @@ import { LoadBalancingConfig } from './load-balancing-config';
 import * as load_balancer_pick_first from './load-balancer-pick-first';
 import * as load_balancer_round_robin from './load-balancer-round-robin';
 import * as load_balancer_priority from './load-balancer-priority';
+import * as load_balancer_weighted_target from './load-balancer-weighted-target';
 
 /**
  * A collection of functions associated with a channel that a load balancer
@@ -139,4 +140,5 @@ export function registerAll() {
   load_balancer_pick_first.setup();
   load_balancer_round_robin.setup();
   load_balancer_priority.setup();
+  load_balancer_weighted_target.setup();
 }

packages/grpc-js/src/load-balancing-config.ts

@@ -48,6 +48,15 @@ export interface PriorityLbConfig {
   priorities: string[];
 }
 
+export interface WeightedTarget {
+  weight: number;
+  child_policy: LoadBalancingConfig[];
+}
+
+export interface WeightedTargetLbConfig {
+  targets: Map<string, WeightedTarget>;
+}
+
 export interface PickFirstLoadBalancingConfig {
   name: 'pick_first';
   pick_first: PickFirstConfig;
@@ -73,12 +82,18 @@ export interface PriorityLoadBalancingConfig {
   priority: PriorityLbConfig;
 }
 
+export interface WeightedTargetLoadBalancingConfig {
+  name: 'weighted_target';
+  weighted_target: WeightedTargetLbConfig;
+}
+
 export type LoadBalancingConfig =
   | PickFirstLoadBalancingConfig
   | RoundRobinLoadBalancingConfig
   | XdsLoadBalancingConfig
   | GrpcLbLoadBalancingConfig
-  | PriorityLoadBalancingConfig;
+  | PriorityLoadBalancingConfig
+  | WeightedTargetLoadBalancingConfig;
 
 export function isRoundRobinLoadBalancingConfig(
   lbconfig: LoadBalancingConfig
@@ -104,6 +119,12 @@ export function isPriorityLoadBalancingConfig(
   return lbconfig.name === 'priority';
 }
 
+export function isWeightedTargetLoadBalancingConfig(
+  lbconfig: LoadBalancingConfig
+): lbconfig is WeightedTargetLoadBalancingConfig {
+  return lbconfig.name === 'weighted_target';
+}
+
 /* In these functions we assume the input came from a JSON object. Therefore we
  * expect that the prototype is uninteresting and that `in` can be used
  * effectively */