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1/*
2 * Copyright 2019 gRPC authors.
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 *
16 */
17
18import {
19 LoadBalancer,
20 ChannelControlHelper,
21 LoadBalancingConfig,
22 registerLoadBalancerType,
23} from './load-balancer';
24import { ConnectivityState } from './connectivity-state';
25import {
26 QueuePicker,
27 Picker,
28 PickArgs,
29 CompletePickResult,
30 PickResultType,
31 UnavailablePicker,
32} from './picker';
33import {
34 SubchannelAddress,
35 subchannelAddressToString,
36} from './subchannel-address';
37import * as logging from './logging';
38import { LogVerbosity } from './constants';
39import { ConnectivityStateListener, SubchannelInterface } from './subchannel-interface';
40
41const TRACER_NAME = 'round_robin';
42
43function trace(text: string): void {
44 logging.trace(LogVerbosity.DEBUG, TRACER_NAME, text);
45}
46
47const TYPE_NAME = 'round_robin';
48
49class RoundRobinLoadBalancingConfig implements LoadBalancingConfig {
50 getLoadBalancerName(): string {
51 return TYPE_NAME;
52 }
53
54 constructor() {}
55
56 toJsonObject(): object {
57 return {
58 [TYPE_NAME]: {},
59 };
60 }
61
62 // eslint-disable-next-line @typescript-eslint/no-explicit-any
63 static createFromJson(obj: any) {
64 return new RoundRobinLoadBalancingConfig();
65 }
66}
67
68class RoundRobinPicker implements Picker {
69 constructor(
70 private readonly subchannelList: SubchannelInterface[],
71 private nextIndex = 0
72 ) {}
73
74 pick(pickArgs: PickArgs): CompletePickResult {
75 const pickedSubchannel = this.subchannelList[this.nextIndex];
76 this.nextIndex = (this.nextIndex + 1) % this.subchannelList.length;
77 return {
78 pickResultType: PickResultType.COMPLETE,
79 subchannel: pickedSubchannel,
80 status: null,
81 extraFilterFactories: [],
82 onCallStarted: null,
83 };
84 }
85
86 /**
87 * Check what the next subchannel returned would be. Used by the load
88 * balancer implementation to preserve this part of the picker state if
89 * possible when a subchannel connects or disconnects.
90 */
91 peekNextSubchannel(): SubchannelInterface {
92 return this.subchannelList[this.nextIndex];
93 }
94}
95
96interface ConnectivityStateCounts {
97 [ConnectivityState.CONNECTING]: number;
98 [ConnectivityState.IDLE]: number;
99 [ConnectivityState.READY]: number;
100 [ConnectivityState.SHUTDOWN]: number;
101 [ConnectivityState.TRANSIENT_FAILURE]: number;
102}
103
104export class RoundRobinLoadBalancer implements LoadBalancer {
105 private subchannels: SubchannelInterface[] = [];
106
107 private currentState: ConnectivityState = ConnectivityState.IDLE;
108
109 private subchannelStateListener: ConnectivityStateListener;
110
111 private subchannelStateCounts: ConnectivityStateCounts;
112
113 private currentReadyPicker: RoundRobinPicker | null = null;
114
115 constructor(private readonly channelControlHelper: ChannelControlHelper) {
116 this.subchannelStateCounts = {
117 [ConnectivityState.CONNECTING]: 0,
118 [ConnectivityState.IDLE]: 0,
119 [ConnectivityState.READY]: 0,
120 [ConnectivityState.SHUTDOWN]: 0,
121 [ConnectivityState.TRANSIENT_FAILURE]: 0,
122 };
123 this.subchannelStateListener = (
124 subchannel: SubchannelInterface,
125 previousState: ConnectivityState,
126 newState: ConnectivityState
127 ) => {
128 this.subchannelStateCounts[previousState] -= 1;
129 this.subchannelStateCounts[newState] += 1;
130 this.calculateAndUpdateState();
131
132 if (
133 newState === ConnectivityState.TRANSIENT_FAILURE ||
134 newState === ConnectivityState.IDLE
135 ) {
136 this.channelControlHelper.requestReresolution();
137 subchannel.startConnecting();
138 }
139 };
140 }
141
142 private calculateAndUpdateState() {
143 if (this.subchannelStateCounts[ConnectivityState.READY] > 0) {
144 const readySubchannels = this.subchannels.filter(
145 (subchannel) =>
146 subchannel.getConnectivityState() === ConnectivityState.READY
147 );
148 let index = 0;
149 if (this.currentReadyPicker !== null) {
150 index = readySubchannels.indexOf(
151 this.currentReadyPicker.peekNextSubchannel()
152 );
153 if (index < 0) {
154 index = 0;
155 }
156 }
157 this.updateState(
158 ConnectivityState.READY,
159 new RoundRobinPicker(readySubchannels, index)
160 );
161 } else if (this.subchannelStateCounts[ConnectivityState.CONNECTING] > 0) {
162 this.updateState(ConnectivityState.CONNECTING, new QueuePicker(this));
163 } else if (
164 this.subchannelStateCounts[ConnectivityState.TRANSIENT_FAILURE] > 0
165 ) {
166 this.updateState(
167 ConnectivityState.TRANSIENT_FAILURE,
168 new UnavailablePicker()
169 );
170 } else {
171 this.updateState(ConnectivityState.IDLE, new QueuePicker(this));
172 }
173 }
174
175 private updateState(newState: ConnectivityState, picker: Picker) {
176 trace(
177 ConnectivityState[this.currentState] +
178 ' -> ' +
179 ConnectivityState[newState]
180 );
181 if (newState === ConnectivityState.READY) {
182 this.currentReadyPicker = picker as RoundRobinPicker;
183 } else {
184 this.currentReadyPicker = null;
185 }
186 this.currentState = newState;
187 this.channelControlHelper.updateState(newState, picker);
188 }
189
190 private resetSubchannelList() {
191 for (const subchannel of this.subchannels) {
192 subchannel.removeConnectivityStateListener(this.subchannelStateListener);
193 subchannel.unref();
194 this.channelControlHelper.removeChannelzChild(subchannel.getChannelzRef());
195 }
196 this.subchannelStateCounts = {
197 [ConnectivityState.CONNECTING]: 0,
198 [ConnectivityState.IDLE]: 0,
199 [ConnectivityState.READY]: 0,
200 [ConnectivityState.SHUTDOWN]: 0,
201 [ConnectivityState.TRANSIENT_FAILURE]: 0,
202 };
203 this.subchannels = [];
204 }
205
206 updateAddressList(
207 addressList: SubchannelAddress[],
208 lbConfig: LoadBalancingConfig
209 ): void {
210 this.resetSubchannelList();
211 trace(
212 'Connect to address list ' +
213 addressList.map((address) => subchannelAddressToString(address))
214 );
215 this.subchannels = addressList.map((address) =>
216 this.channelControlHelper.createSubchannel(address, {})
217 );
218 for (const subchannel of this.subchannels) {
219 subchannel.ref();
220 subchannel.addConnectivityStateListener(this.subchannelStateListener);
221 this.channelControlHelper.addChannelzChild(subchannel.getChannelzRef());
222 const subchannelState = subchannel.getConnectivityState();
223 this.subchannelStateCounts[subchannelState] += 1;
224 if (
225 subchannelState === ConnectivityState.IDLE ||
226 subchannelState === ConnectivityState.TRANSIENT_FAILURE
227 ) {
228 subchannel.startConnecting();
229 }
230 }
231 this.calculateAndUpdateState();
232 }
233
234 exitIdle(): void {
235 for (const subchannel of this.subchannels) {
236 subchannel.startConnecting();
237 }
238 }
239 resetBackoff(): void {
240 /* The pick first load balancer does not have a connection backoff, so this
241 * does nothing */
242 }
243 destroy(): void {
244 this.resetSubchannelList();
245 }
246 getTypeName(): string {
247 return TYPE_NAME;
248 }
249}
250
251export function setup() {
252 registerLoadBalancerType(
253 TYPE_NAME,
254 RoundRobinLoadBalancer,
255 RoundRobinLoadBalancingConfig
256 );
257}