@grpc/grpc-js/src/load-balancer-outlier-detection.ts

/*
 * Copyright 2022 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 { ChannelOptions } from './channel-options';
import { ConnectivityState } from './connectivity-state';
import { LogVerbosity, Status } from './constants';
import { Duration, durationToMs, isDuration, msToDuration } from './duration';
import {
  ChannelControlHelper,
  createChildChannelControlHelper,
  registerLoadBalancerType,
} from './experimental';
import {
  selectLbConfigFromList,
  LoadBalancer,
  TypedLoadBalancingConfig,
} from './load-balancer';
import { ChildLoadBalancerHandler } from './load-balancer-child-handler';
import { PickArgs, Picker, PickResult, PickResultType } from './picker';
import {
  Endpoint,
  EndpointMap,
  SubchannelAddress,
  endpointToString,
} from './subchannel-address';
import {
  BaseSubchannelWrapper,
  SubchannelInterface,
} from './subchannel-interface';
import * as logging from './logging';
import { LoadBalancingConfig } from './service-config';

const TRACER_NAME = 'outlier_detection';

function trace(text: string): void {
  logging.trace(LogVerbosity.DEBUG, TRACER_NAME, text);
}

const TYPE_NAME = 'outlier_detection';

const OUTLIER_DETECTION_ENABLED =
  (process.env.GRPC_EXPERIMENTAL_ENABLE_OUTLIER_DETECTION ?? 'true') === 'true';

export interface SuccessRateEjectionConfig {
  readonly stdev_factor: number;
  readonly enforcement_percentage: number;
  readonly minimum_hosts: number;
  readonly request_volume: number;
}

export interface FailurePercentageEjectionConfig {
  readonly threshold: number;
  readonly enforcement_percentage: number;
  readonly minimum_hosts: number;
  readonly request_volume: number;
}

export interface OutlierDetectionRawConfig {
  interval?: Duration;
  base_ejection_time?: Duration;
  max_ejection_time?: Duration;
  max_ejection_percent?: number;
  success_rate_ejection?: Partial<SuccessRateEjectionConfig>;
  failure_percentage_ejection?: Partial<FailurePercentageEjectionConfig>;
  child_policy: LoadBalancingConfig[];
}

const defaultSuccessRateEjectionConfig: SuccessRateEjectionConfig = {
  stdev_factor: 1900,
  enforcement_percentage: 100,
  minimum_hosts: 5,
  request_volume: 100,
};

const defaultFailurePercentageEjectionConfig: FailurePercentageEjectionConfig =
  {
    threshold: 85,
    enforcement_percentage: 100,
    minimum_hosts: 5,
    request_volume: 50,
  };

type TypeofValues =
  | 'object'
  | 'boolean'
  | 'function'
  | 'number'
  | 'string'
  | 'undefined';

function validateFieldType(
  obj: any,
  fieldName: string,
  expectedType: TypeofValues,
  objectName?: string
) {
  if (
    fieldName in obj &&
    obj[fieldName] !== undefined &&
    typeof obj[fieldName] !== expectedType
  ) {
    const fullFieldName = objectName ? `${objectName}.${fieldName}` : fieldName;
    throw new Error(
      `outlier detection config ${fullFieldName} parse error: expected ${expectedType}, got ${typeof obj[
        fieldName
      ]}`
    );
  }
}

function validatePositiveDuration(
  obj: any,
  fieldName: string,
  objectName?: string
) {
  const fullFieldName = objectName ? `${objectName}.${fieldName}` : fieldName;
  if (fieldName in obj && obj[fieldName] !== undefined) {
    if (!isDuration(obj[fieldName])) {
      throw new Error(
        `outlier detection config ${fullFieldName} parse error: expected Duration, got ${typeof obj[
          fieldName
        ]}`
      );
    }
    if (
      !(
        obj[fieldName].seconds >= 0 &&
        obj[fieldName].seconds <= 315_576_000_000 &&
        obj[fieldName].nanos >= 0 &&
        obj[fieldName].nanos <= 999_999_999
      )
    ) {
      throw new Error(
        `outlier detection config ${fullFieldName} parse error: values out of range for non-negative Duaration`
      );
    }
  }
}

function validatePercentage(obj: any, fieldName: string, objectName?: string) {
  const fullFieldName = objectName ? `${objectName}.${fieldName}` : fieldName;
  validateFieldType(obj, fieldName, 'number', objectName);
  if (
    fieldName in obj &&
    obj[fieldName] !== undefined &&
    !(obj[fieldName] >= 0 && obj[fieldName] <= 100)
  ) {
    throw new Error(
      `outlier detection config ${fullFieldName} parse error: value out of range for percentage (0-100)`
    );
  }
}

export class OutlierDetectionLoadBalancingConfig
  implements TypedLoadBalancingConfig
{
  private readonly intervalMs: number;
  private readonly baseEjectionTimeMs: number;
  private readonly maxEjectionTimeMs: number;
  private readonly maxEjectionPercent: number;
  private readonly successRateEjection: SuccessRateEjectionConfig | null;
  private readonly failurePercentageEjection: FailurePercentageEjectionConfig | null;

  constructor(
    intervalMs: number | null,
    baseEjectionTimeMs: number | null,
    maxEjectionTimeMs: number | null,
    maxEjectionPercent: number | null,
    successRateEjection: Partial<SuccessRateEjectionConfig> | null,
    failurePercentageEjection: Partial<FailurePercentageEjectionConfig> | null,
    private readonly childPolicy: TypedLoadBalancingConfig
  ) {
    if (childPolicy.getLoadBalancerName() === 'pick_first') {
      throw new Error(
        'outlier_detection LB policy cannot have a pick_first child policy'
      );
    }
    this.intervalMs = intervalMs ?? 10_000;
    this.baseEjectionTimeMs = baseEjectionTimeMs ?? 30_000;
    this.maxEjectionTimeMs = maxEjectionTimeMs ?? 300_000;
    this.maxEjectionPercent = maxEjectionPercent ?? 10;
    this.successRateEjection = successRateEjection
      ? { ...defaultSuccessRateEjectionConfig, ...successRateEjection }
      : null;
    this.failurePercentageEjection = failurePercentageEjection
      ? {
          ...defaultFailurePercentageEjectionConfig,
          ...failurePercentageEjection,
        }
      : null;
  }
  getLoadBalancerName(): string {
    return TYPE_NAME;
  }
  toJsonObject(): object {
    return {
      outlier_detection: {
        interval: msToDuration(this.intervalMs),
        base_ejection_time: msToDuration(this.baseEjectionTimeMs),
        max_ejection_time: msToDuration(this.maxEjectionTimeMs),
        max_ejection_percent: this.maxEjectionPercent,
        success_rate_ejection: this.successRateEjection ?? undefined,
        failure_percentage_ejection:
          this.failurePercentageEjection ?? undefined,
        child_policy: [this.childPolicy.toJsonObject()],
      },
    };
  }

  getIntervalMs(): number {
    return this.intervalMs;
  }
  getBaseEjectionTimeMs(): number {
    return this.baseEjectionTimeMs;
  }
  getMaxEjectionTimeMs(): number {
    return this.maxEjectionTimeMs;
  }
  getMaxEjectionPercent(): number {
    return this.maxEjectionPercent;
  }
  getSuccessRateEjectionConfig(): SuccessRateEjectionConfig | null {
    return this.successRateEjection;
  }
  getFailurePercentageEjectionConfig(): FailurePercentageEjectionConfig | null {
    return this.failurePercentageEjection;
  }
  getChildPolicy(): TypedLoadBalancingConfig {
    return this.childPolicy;
  }

  static createFromJson(obj: any): OutlierDetectionLoadBalancingConfig {
    validatePositiveDuration(obj, 'interval');
    validatePositiveDuration(obj, 'base_ejection_time');
    validatePositiveDuration(obj, 'max_ejection_time');
    validatePercentage(obj, 'max_ejection_percent');
    if (
      'success_rate_ejection' in obj &&
      obj.success_rate_ejection !== undefined
    ) {
      if (typeof obj.success_rate_ejection !== 'object') {
        throw new Error(
          'outlier detection config success_rate_ejection must be an object'
        );
      }
      validateFieldType(
        obj.success_rate_ejection,
        'stdev_factor',
        'number',
        'success_rate_ejection'
      );
      validatePercentage(
        obj.success_rate_ejection,
        'enforcement_percentage',
        'success_rate_ejection'
      );
      validateFieldType(
        obj.success_rate_ejection,
        'minimum_hosts',
        'number',
        'success_rate_ejection'
      );
      validateFieldType(
        obj.success_rate_ejection,
        'request_volume',
        'number',
        'success_rate_ejection'
      );
    }
    if (
      'failure_percentage_ejection' in obj &&
      obj.failure_percentage_ejection !== undefined
    ) {
      if (typeof obj.failure_percentage_ejection !== 'object') {
        throw new Error(
          'outlier detection config failure_percentage_ejection must be an object'
        );
      }
      validatePercentage(
        obj.failure_percentage_ejection,
        'threshold',
        'failure_percentage_ejection'
      );
      validatePercentage(
        obj.failure_percentage_ejection,
        'enforcement_percentage',
        'failure_percentage_ejection'
      );
      validateFieldType(
        obj.failure_percentage_ejection,
        'minimum_hosts',
        'number',
        'failure_percentage_ejection'
      );
      validateFieldType(
        obj.failure_percentage_ejection,
        'request_volume',
        'number',
        'failure_percentage_ejection'
      );
    }

    if (!('child_policy' in obj) || !Array.isArray(obj.child_policy)) {
      throw new Error('outlier detection config child_policy must be an array');
    }
    const childPolicy = selectLbConfigFromList(obj.child_policy);
    if (!childPolicy) {
      throw new Error(
        'outlier detection config child_policy: no valid recognized policy found'
      );
    }

    return new OutlierDetectionLoadBalancingConfig(
      obj.interval ? durationToMs(obj.interval) : null,
      obj.base_ejection_time ? durationToMs(obj.base_ejection_time) : null,
      obj.max_ejection_time ? durationToMs(obj.max_ejection_time) : null,
      obj.max_ejection_percent ?? null,
      obj.success_rate_ejection,
      obj.failure_percentage_ejection,
      childPolicy
    );
  }
}

class OutlierDetectionSubchannelWrapper
  extends BaseSubchannelWrapper
  implements SubchannelInterface
{
  private refCount = 0;
  constructor(
    childSubchannel: SubchannelInterface,
    private mapEntry?: MapEntry
  ) {
    super(childSubchannel);
  }

  ref() {
    this.child.ref();
    this.refCount += 1;
  }

  unref() {
    this.child.unref();
    this.refCount -= 1;
    if (this.refCount <= 0) {
      if (this.mapEntry) {
        const index = this.mapEntry.subchannelWrappers.indexOf(this);
        if (index >= 0) {
          this.mapEntry.subchannelWrappers.splice(index, 1);
        }
      }
    }
  }

  eject() {
    this.setHealthy(false);
  }

  uneject() {
    this.setHealthy(true);
  }

  getMapEntry(): MapEntry | undefined {
    return this.mapEntry;
  }

  getWrappedSubchannel(): SubchannelInterface {
    return this.child;
  }
}

interface CallCountBucket {
  success: number;
  failure: number;
}

function createEmptyBucket(): CallCountBucket {
  return {
    success: 0,
    failure: 0,
  };
}

class CallCounter {
  private activeBucket: CallCountBucket = createEmptyBucket();
  private inactiveBucket: CallCountBucket = createEmptyBucket();
  addSuccess() {
    this.activeBucket.success += 1;
  }
  addFailure() {
    this.activeBucket.failure += 1;
  }
  switchBuckets() {
    this.inactiveBucket = this.activeBucket;
    this.activeBucket = createEmptyBucket();
  }
  getLastSuccesses() {
    return this.inactiveBucket.success;
  }
  getLastFailures() {
    return this.inactiveBucket.failure;
  }
}

class OutlierDetectionPicker implements Picker {
  constructor(private wrappedPicker: Picker, private countCalls: boolean) {}
  pick(pickArgs: PickArgs): PickResult {
    const wrappedPick = this.wrappedPicker.pick(pickArgs);
    if (wrappedPick.pickResultType === PickResultType.COMPLETE) {
      const subchannelWrapper =
        wrappedPick.subchannel as OutlierDetectionSubchannelWrapper;
      const mapEntry = subchannelWrapper.getMapEntry();
      if (mapEntry) {
        let onCallEnded = wrappedPick.onCallEnded;
        if (this.countCalls) {
          onCallEnded = statusCode => {
            if (statusCode === Status.OK) {
              mapEntry.counter.addSuccess();
            } else {
              mapEntry.counter.addFailure();
            }
            wrappedPick.onCallEnded?.(statusCode);
          };
        }
        return {
          ...wrappedPick,
          subchannel: subchannelWrapper.getWrappedSubchannel(),
          onCallEnded: onCallEnded,
        };
      } else {
        return {
          ...wrappedPick,
          subchannel: subchannelWrapper.getWrappedSubchannel(),
        };
      }
    } else {
      return wrappedPick;
    }
  }
}

interface MapEntry {
  counter: CallCounter;
  currentEjectionTimestamp: Date | null;
  ejectionTimeMultiplier: number;
  subchannelWrappers: OutlierDetectionSubchannelWrapper[];
}

export class OutlierDetectionLoadBalancer implements LoadBalancer {
  private childBalancer: ChildLoadBalancerHandler;
  private entryMap = new EndpointMap<MapEntry>();
  private latestConfig: OutlierDetectionLoadBalancingConfig | null = null;
  private ejectionTimer: NodeJS.Timeout;
  private timerStartTime: Date | null = null;

  constructor(
    channelControlHelper: ChannelControlHelper,
    options: ChannelOptions
  ) {
    this.childBalancer = new ChildLoadBalancerHandler(
      createChildChannelControlHelper(channelControlHelper, {
        createSubchannel: (
          subchannelAddress: SubchannelAddress,
          subchannelArgs: ChannelOptions
        ) => {
          const originalSubchannel = channelControlHelper.createSubchannel(
            subchannelAddress,
            subchannelArgs
          );
          const mapEntry =
            this.entryMap.getForSubchannelAddress(subchannelAddress);
          const subchannelWrapper = new OutlierDetectionSubchannelWrapper(
            originalSubchannel,
            mapEntry
          );
          if (mapEntry?.currentEjectionTimestamp !== null) {
            // If the address is ejected, propagate that to the new subchannel wrapper
            subchannelWrapper.eject();
          }
          mapEntry?.subchannelWrappers.push(subchannelWrapper);
          return subchannelWrapper;
        },
        updateState: (connectivityState: ConnectivityState, picker: Picker) => {
          if (connectivityState === ConnectivityState.READY) {
            channelControlHelper.updateState(
              connectivityState,
              new OutlierDetectionPicker(picker, this.isCountingEnabled())
            );
          } else {
            channelControlHelper.updateState(connectivityState, picker);
          }
        },
      }),
      options
    );
    this.ejectionTimer = setInterval(() => {}, 0);
    clearInterval(this.ejectionTimer);
  }

  private isCountingEnabled(): boolean {
    return (
      this.latestConfig !== null &&
      (this.latestConfig.getSuccessRateEjectionConfig() !== null ||
        this.latestConfig.getFailurePercentageEjectionConfig() !== null)
    );
  }

  private getCurrentEjectionPercent() {
    let ejectionCount = 0;
    for (const mapEntry of this.entryMap.values()) {
      if (mapEntry.currentEjectionTimestamp !== null) {
        ejectionCount += 1;
      }
    }
    return (ejectionCount * 100) / this.entryMap.size;
  }

  private runSuccessRateCheck(ejectionTimestamp: Date) {
    if (!this.latestConfig) {
      return;
    }
    const successRateConfig = this.latestConfig.getSuccessRateEjectionConfig();
    if (!successRateConfig) {
      return;
    }
    trace('Running success rate check');
    // Step 1
    const targetRequestVolume = successRateConfig.request_volume;
    let addresesWithTargetVolume = 0;
    const successRates: number[] = [];
    for (const [endpoint, mapEntry] of this.entryMap.entries()) {
      const successes = mapEntry.counter.getLastSuccesses();
      const failures = mapEntry.counter.getLastFailures();
      trace(
        'Stats for ' +
          endpointToString(endpoint) +
          ': successes=' +
          successes +
          ' failures=' +
          failures +
          ' targetRequestVolume=' +
          targetRequestVolume
      );
      if (successes + failures >= targetRequestVolume) {
        addresesWithTargetVolume += 1;
        successRates.push(successes / (successes + failures));
      }
    }
    trace(
      'Found ' +
        addresesWithTargetVolume +
        ' success rate candidates; currentEjectionPercent=' +
        this.getCurrentEjectionPercent() +
        ' successRates=[' +
        successRates +
        ']'
    );
    if (addresesWithTargetVolume < successRateConfig.minimum_hosts) {
      return;
    }

    // Step 2
    const successRateMean =
      successRates.reduce((a, b) => a + b) / successRates.length;
    let successRateDeviationSum = 0;
    for (const rate of successRates) {
      const deviation = rate - successRateMean;
      successRateDeviationSum += deviation * deviation;
    }
    const successRateVariance = successRateDeviationSum / successRates.length;
    const successRateStdev = Math.sqrt(successRateVariance);
    const ejectionThreshold =
      successRateMean -
      successRateStdev * (successRateConfig.stdev_factor / 1000);
    trace(
      'stdev=' + successRateStdev + ' ejectionThreshold=' + ejectionThreshold
    );

    // Step 3
    for (const [address, mapEntry] of this.entryMap.entries()) {
      // Step 3.i
      if (
        this.getCurrentEjectionPercent() >=
        this.latestConfig.getMaxEjectionPercent()
      ) {
        break;
      }
      // Step 3.ii
      const successes = mapEntry.counter.getLastSuccesses();
      const failures = mapEntry.counter.getLastFailures();
      if (successes + failures < targetRequestVolume) {
        continue;
      }
      // Step 3.iii
      const successRate = successes / (successes + failures);
      trace('Checking candidate ' + address + ' successRate=' + successRate);
      if (successRate < ejectionThreshold) {
        const randomNumber = Math.random() * 100;
        trace(
          'Candidate ' +
            address +
            ' randomNumber=' +
            randomNumber +
            ' enforcement_percentage=' +
            successRateConfig.enforcement_percentage
        );
        if (randomNumber < successRateConfig.enforcement_percentage) {
          trace('Ejecting candidate ' + address);
          this.eject(mapEntry, ejectionTimestamp);
        }
      }
    }
  }

  private runFailurePercentageCheck(ejectionTimestamp: Date) {
    if (!this.latestConfig) {
      return;
    }
    const failurePercentageConfig =
      this.latestConfig.getFailurePercentageEjectionConfig();
    if (!failurePercentageConfig) {
      return;
    }
    trace(
      'Running failure percentage check. threshold=' +
        failurePercentageConfig.threshold +
        ' request volume threshold=' +
        failurePercentageConfig.request_volume
    );
    // Step 1
    let addressesWithTargetVolume = 0;
    for (const mapEntry of this.entryMap.values()) {
      const successes = mapEntry.counter.getLastSuccesses();
      const failures = mapEntry.counter.getLastFailures();
      if (successes + failures >= failurePercentageConfig.request_volume) {
        addressesWithTargetVolume += 1;
      }
    }
    if (addressesWithTargetVolume < failurePercentageConfig.minimum_hosts) {
      return;
    }

    // Step 2
    for (const [address, mapEntry] of this.entryMap.entries()) {
      // Step 2.i
      if (
        this.getCurrentEjectionPercent() >=
        this.latestConfig.getMaxEjectionPercent()
      ) {
        break;
      }
      // Step 2.ii
      const successes = mapEntry.counter.getLastSuccesses();
      const failures = mapEntry.counter.getLastFailures();
      trace('Candidate successes=' + successes + ' failures=' + failures);
      if (successes + failures < failurePercentageConfig.request_volume) {
        continue;
      }
      // Step 2.iii
      const failurePercentage = (failures * 100) / (failures + successes);
      if (failurePercentage > failurePercentageConfig.threshold) {
        const randomNumber = Math.random() * 100;
        trace(
          'Candidate ' +
            address +
            ' randomNumber=' +
            randomNumber +
            ' enforcement_percentage=' +
            failurePercentageConfig.enforcement_percentage
        );
        if (randomNumber < failurePercentageConfig.enforcement_percentage) {
          trace('Ejecting candidate ' + address);
          this.eject(mapEntry, ejectionTimestamp);
        }
      }
    }
  }

  private eject(mapEntry: MapEntry, ejectionTimestamp: Date) {
    mapEntry.currentEjectionTimestamp = new Date();
    mapEntry.ejectionTimeMultiplier += 1;
    for (const subchannelWrapper of mapEntry.subchannelWrappers) {
      subchannelWrapper.eject();
    }
  }

  private uneject(mapEntry: MapEntry) {
    mapEntry.currentEjectionTimestamp = null;
    for (const subchannelWrapper of mapEntry.subchannelWrappers) {
      subchannelWrapper.uneject();
    }
  }

  private switchAllBuckets() {
    for (const mapEntry of this.entryMap.values()) {
      mapEntry.counter.switchBuckets();
    }
  }

  private startTimer(delayMs: number) {
    this.ejectionTimer = setTimeout(() => this.runChecks(), delayMs);
    this.ejectionTimer.unref?.();
  }

  private runChecks() {
    const ejectionTimestamp = new Date();
    trace('Ejection timer running');

    this.switchAllBuckets();

    if (!this.latestConfig) {
      return;
    }
    this.timerStartTime = ejectionTimestamp;
    this.startTimer(this.latestConfig.getIntervalMs());

    this.runSuccessRateCheck(ejectionTimestamp);
    this.runFailurePercentageCheck(ejectionTimestamp);

    for (const [address, mapEntry] of this.entryMap.entries()) {
      if (mapEntry.currentEjectionTimestamp === null) {
        if (mapEntry.ejectionTimeMultiplier > 0) {
          mapEntry.ejectionTimeMultiplier -= 1;
        }
      } else {
        const baseEjectionTimeMs = this.latestConfig.getBaseEjectionTimeMs();
        const maxEjectionTimeMs = this.latestConfig.getMaxEjectionTimeMs();
        const returnTime = new Date(
          mapEntry.currentEjectionTimestamp.getTime()
        );
        returnTime.setMilliseconds(
          returnTime.getMilliseconds() +
            Math.min(
              baseEjectionTimeMs * mapEntry.ejectionTimeMultiplier,
              Math.max(baseEjectionTimeMs, maxEjectionTimeMs)
            )
        );
        if (returnTime < new Date()) {
          trace('Unejecting ' + address);
          this.uneject(mapEntry);
        }
      }
    }
  }

  updateAddressList(
    endpointList: Endpoint[],
    lbConfig: TypedLoadBalancingConfig,
    attributes: { [key: string]: unknown }
  ): void {
    if (!(lbConfig instanceof OutlierDetectionLoadBalancingConfig)) {
      return;
    }
    for (const endpoint of endpointList) {
      if (!this.entryMap.has(endpoint)) {
        trace('Adding map entry for ' + endpointToString(endpoint));
        this.entryMap.set(endpoint, {
          counter: new CallCounter(),
          currentEjectionTimestamp: null,
          ejectionTimeMultiplier: 0,
          subchannelWrappers: [],
        });
      }
    }
    this.entryMap.deleteMissing(endpointList);
    const childPolicy = lbConfig.getChildPolicy();
    this.childBalancer.updateAddressList(endpointList, childPolicy, attributes);

    if (
      lbConfig.getSuccessRateEjectionConfig() ||
      lbConfig.getFailurePercentageEjectionConfig()
    ) {
      if (this.timerStartTime) {
        trace('Previous timer existed. Replacing timer');
        clearTimeout(this.ejectionTimer);
        const remainingDelay =
          lbConfig.getIntervalMs() -
          (new Date().getTime() - this.timerStartTime.getTime());
        this.startTimer(remainingDelay);
      } else {
        trace('Starting new timer');
        this.timerStartTime = new Date();
        this.startTimer(lbConfig.getIntervalMs());
        this.switchAllBuckets();
      }
    } else {
      trace('Counting disabled. Cancelling timer.');
      this.timerStartTime = null;
      clearTimeout(this.ejectionTimer);
      for (const mapEntry of this.entryMap.values()) {
        this.uneject(mapEntry);
        mapEntry.ejectionTimeMultiplier = 0;
      }
    }

    this.latestConfig = lbConfig;
  }
  exitIdle(): void {
    this.childBalancer.exitIdle();
  }
  resetBackoff(): void {
    this.childBalancer.resetBackoff();
  }
  destroy(): void {
    clearTimeout(this.ejectionTimer);
    this.childBalancer.destroy();
  }
  getTypeName(): string {
    return TYPE_NAME;
  }
}

export function setup() {
  if (OUTLIER_DETECTION_ENABLED) {
    registerLoadBalancerType(
      TYPE_NAME,
      OutlierDetectionLoadBalancer,
      OutlierDetectionLoadBalancingConfig
    );
  }
}