wip

extensions/oplogPopulator/OplogPopulator.js

@@ -51,7 +51,7 @@ class OplogPopulator {
         this._logger = params.logger;
         this._changeStreamWrapper = null;
         this._allocator = null;
-        this._connectorsManager  = null;
+        this._connectorsManager = null;
         // contains OplogPopulatorUtils class of each supported extension
         this._extHelpers = {};
         // MongoDB related
@@ -78,9 +78,9 @@ class OplogPopulator {
     async _setupMongoClient() {
         try {
             const client = await MongoClient.connect(this._mongoUrl, {
-                 replicaSet: this._replicaSet,
-                 useNewUrlParser: true,
-                 useUnifiedTopology: true,
+                replicaSet: this._replicaSet,
+                useNewUrlParser: true,
+                useUnifiedTopology: true,
             });
             // connect to metadata DB
             this._mongoClient = client.db(this._database, {
@@ -185,7 +185,7 @@ class OplogPopulator {
                 // remove bucket if no longer backbeat enabled
                 if (isListeningToBucket && !isBackbeatEnabled) {
                     await this._allocator.stopListeningToBucket(change.documentKey._id);
-                // add bucket if it became backbeat enabled
+                    // add bucket if it became backbeat enabled
                 } else if (!isListeningToBucket && isBackbeatEnabled) {
                     await this._allocator.listenToBucket(change.documentKey._id, eventDate);
                 }
@@ -242,35 +242,65 @@ class OplogPopulator {
         this._changeStreamWrapper.start();
     }
 
+    _isPipelineImmutable() {
+        return semver.gte(this._mongoVersion, constants.mongodbVersionWithImmutablePipelines);
+    }
+
     /**
      * Sets the OplogPopulator
      * @returns {Promise|undefined} undefined
      * @throws {InternalError}
      */
     async setup() {
-       try {
-           this._loadOplogHelperClasses();
-           this._connectorsManager = new ConnectorsManager({
-               nbConnectors: this._config.numberOfConnectors,
-               database: this._database,
-               mongoUrl: this._mongoUrl,
-               oplogTopic: this._config.topic,
-               cronRule: this._config.connectorsUpdateCronRule,
-               prefix: this._config.prefix,
-               heartbeatIntervalMs: this._config.heartbeatIntervalMs,
-               kafkaConnectHost: this._config.kafkaConnectHost,
-               kafkaConnectPort: this._config.kafkaConnectPort,
-               metricsHandler: this._metricsHandler,
-               logger: this._logger,
+        try {
+            this._loadOplogHelperClasses();
+            // initialize mongo client
+            await this._setupMongoClient();
+
+            if (this._isPipelineImmutable()) {
+                // In this case, mongodb does not support reusing a
+                // resume token from a different pipeline. In other
+                // words, we cannot alter an existing pipeline. In this
+                // case, the strategy is to allow a maximum of one
+                // bucket per kafka connector.
+                this._maximumBucketsPerConnector = 1;
+            } else {
+                // In this case, we can have multiple buckets per
+                // kafka connector. However, we want to proactively
+                // ensure that the pipeline will be accepted by
+                // mongodb.
+                this._maximumBucketsPerConnector = constants.maxBucketPerConnector;
+            }
+
+            // If the flag useSingleChangeStream is set to true, we
+            // set the max number to infinity, and the number of connectors
+            // to 1.
+            if (this._config.changeStream.singleChangeStream) {
+                this._maximumBucketsPerConnector = Infinity;
+                this._config.numberOfConnectors = 1;
+            }
+            this._connectorsManager = new ConnectorsManager({
+                nbConnectors: this._config.numberOfConnectors,
+                singleChangeStream: this._config.changeStream.singleChangeStream,
+                isPipelineImmutable: this._isPipelineImmutable(),
+                database: this._database,
+                mongoUrl: this._mongoUrl,
+                oplogTopic: this._config.topic,
+                cronRule: this._config.connectorsUpdateCronRule,
+                prefix: this._config.prefix,
+                heartbeatIntervalMs: this._config.heartbeatIntervalMs,
+                kafkaConnectHost: this._config.kafkaConnectHost,
+                kafkaConnectPort: this._config.kafkaConnectPort,
+                metricsHandler: this._metricsHandler,
+                logger: this._logger,
             });
             await this._connectorsManager.initializeConnectors();
             this._allocator = new Allocator({
                 connectorsManager: this._connectorsManager,
                 metricsHandler: this._metricsHandler,
+                maximumBucketsPerConnector: this._maximumBucketsPerConnector,
                 logger: this._logger,
             });
-            // initialize mongo client
-            await this._setupMongoClient();
             // get currently valid buckets from mongo
             const validBuckets = await this._getBackbeatEnabledBuckets();
             // listen to valid buckets
@@ -291,13 +321,13 @@ class OplogPopulator {
             this._logger.info('OplogPopulator setup complete', {
                 method: 'OplogPopulator.setup',
             });
-       } catch (err) {
+        } catch (err) {
             this._logger.error('An error occured when setting up the OplogPopulator', {
                 method: 'OplogPopulator.setup',
                 error: err.description || err.message,
             });
             throw errors.InternalError.customizeDescription(err.description);
-       }
+        }
     }
 
     /**

extensions/oplogPopulator/OplogPopulatorConfigValidator.js

@@ -10,6 +10,7 @@ const joiSchema = joi.object({
     probeServer: probeServerJoi.default(),
     connectorsUpdateCronRule: joi.string().default('*/1 * * * * *'),
     heartbeatIntervalMs: joi.number().default(10000),
+    singleChangeStream: joi.boolean().default(false),
 });
 
 function configValidator(backbeatConfig, extConfig) {

extensions/oplogPopulator/allocationStrategy/AllocationStrategy.js

@@ -4,10 +4,15 @@ class AllocationStrategy {
 
     /**
      * @constructor
-     * @param {Logger} logger logger object
+     * @param {Object} params params
+     * @param {Number} params.maximumBucketsPerConnector maximum number of buckets per connector
+     * @param {Function} params.addConnector function to add a connector
+     * @param {Logger} params.logger logger object
      */
-    constructor(logger) {
-        this._logger = logger;
+    constructor(params) {
+        this._logger = params.logger;
+        this.maximumBucketsPerConnector = params.maximumBucketsPerConnector;
+        this._addConnector = params.addConnector.bind(this);
     }
 
     /**

extensions/oplogPopulator/allocationStrategy/LeastFullConnector.js

@@ -1,3 +1,4 @@
+const { maximumBucketsPerConnector } = require('../constants');
 const AllocationStrategy = require('./AllocationStrategy');
 
 /**
@@ -6,26 +7,22 @@ const AllocationStrategy = require('./AllocationStrategy');
  * @classdesc LeastFullConnector is an allocation
  * strategy that assigns buckets to connectors based
  * on the number of buckets assigned to each connector.
- * Connectors with the fewest buckets are filled first
+ * Connectors with the fewest buckets are filled first.
+ * If a connector reached the maximum number of buckets,
+ * a new connector is created.
  */
 class LeastFullConnector extends AllocationStrategy {
-
-    /**
-     * @constructor
-     * @param {Object} params params
-     * @param {Logger} params.logger logger object
-     */
-    constructor(params) {
-        super(params.logger);
-    }
-
     /**
      * Get best connector for assigning a bucket
      * @param {Connector[]} connectors available connectors
      * @returns {Connector} connector
      */
     getConnector(connectors) {
-        return connectors.reduce((prev, elt) => (elt.bucketCount < prev.bucketCount ? elt : prev));
+        const connector = connectors.reduce((prev, elt) => (elt.bucketCount < prev.bucketCount ? elt : prev));
+        if (connector.buckets.length >= maximumBucketsPerConnector) {
+            return this._addConnector();
+        }
+        return connector;
     }
 }
 

extensions/oplogPopulator/constants.js

@@ -1,6 +1,12 @@
 const constants = {
+    internalMongoDBCollectionPrefix: '__',
     bucketMetastore: '__metastore',
     defaultConnectorName: 'source-connector',
+    // Max length in a pipeline is equal to the MongoDB BSON max document size,
+    // so 16MB. To allow for other parameters in the pipeline, we round the max
+    // to 16 MB (16777216B) / 64 (max length of a bucket name) ~= 260000
+    maxBucketPerConnector: 260000,
+    mongodbVersionWithImmutablePipelines: '6.0.0',
     defaultConnectorConfig: {
         'connector.class': 'com.mongodb.kafka.connect.MongoSourceConnector',
         'pipeline': '[]',

extensions/oplogPopulator/modules/Allocator.js

@@ -3,9 +3,11 @@ const { errors } = require('arsenal');
 
 const OplogPopulatorMetrics = require('../OplogPopulatorMetrics');
 const LeastFullConnector = require('../allocationStrategy/LeastFullConnector');
+const constants = require('../constants');
 
 const paramsJoi = joi.object({
     connectorsManager: joi.object().required(),
+    maximumBucketsPerConnector: joi.number().default(constants.maxBucketPerConnector),
     metricsHandler: joi.object()
         .instance(OplogPopulatorMetrics).required(),
     logger: joi.object().required(),
@@ -31,6 +33,8 @@ class Allocator {
         this._logger = params.logger;
         this._allocationStrategy = new LeastFullConnector({
             logger: params.logger,
+            maximumBucketsPerConnector: params.maximumBucketsPerConnector,
+            addConnector: this._connectorsManager.addConnector.bind(this._connectorsManager),
         });
         this._metricsHandler = params.metricsHandler;
         // Stores connector assigned for each bucket

extensions/oplogPopulator/modules/Connector.js

@@ -2,6 +2,7 @@ const joi = require('joi');
 const uuid = require('uuid');
 const { errors } = require('arsenal');
 const KafkaConnectWrapper = require('../../../lib/wrappers/KafkaConnectWrapper');
+const constants = require('../constants');
 
 const connectorParams = joi.object({
     name: joi.string().required(),
@@ -11,6 +12,9 @@ const connectorParams = joi.object({
     logger: joi.object().required(),
     kafkaConnectHost: joi.string().required(),
     kafkaConnectPort: joi.number().required(),
+    maximumBucketsPerConnector: joi.number().default(constants.maxBucketPerConnector),
+    isPipelineImmutable: joi.boolean().default(false),
+    singleChangeStream: joi.boolean().default(false),
 });
 
 /**
@@ -34,6 +38,10 @@ class Connector {
      * @param {Logger} params.logger logger object
      * @param {string} params.kafkaConnectHost kafka connect host
      * @param {number} params.kafkaConnectPort kafka connect port
+     * @param {number} params.maximumBucketsPerConnector maximum number of
+     * buckets per connector
+     * @param {Boolean} params.singleChangeStream if true, one connector binds to
+     * one bucket maximum
      */
     constructor(params) {
         joi.attempt(params, connectorParams);
@@ -59,6 +67,9 @@ class Connector {
             kafkaConnectPort: params.kafkaConnectPort,
             logger: this._logger,
         });
+        this._singleChangeStream = params.singleChangeStream;
+        this._maximumBucketsPerConnector = params.maximumBucketsPerConnector;
+        this._isPipelineImmutable = params.isPipelineImmutable;
     }
 
     /**
@@ -233,6 +244,9 @@ class Connector {
      * @throws {InternalError}
      */
     async addBucket(bucket, doUpdate = false) {
+        if (this._buckets.size > this._maximumBucketsPerConnector) {
+            throw errors.InternalError.customizeDescription('Connector reached maximum number of buckets');
+        }
         this._buckets.add(bucket);
         this._updateConnectorState(true);
         try {
@@ -260,7 +274,19 @@ class Connector {
         this._buckets.delete(bucket);
         this._updateConnectorState(true);
         try {
-            await this.updatePipeline(doUpdate);
+            if (this._isPipelineImmutable && this._buckets.size > 1) {
+                this.logger.warning('Removing a bucket from an immutable pipeline', {
+                    method: 'Connector.removeBucket',
+                    connector: this._name,
+                    bucket,
+                });
+            } else if (this._isPipelineImmutable) {
+                // If the pipeline is immutable and only one bucket is left,
+                // we can destroy the connector, so it will be recreated with
+                // a new bucket later.
+                return this.destroy();
+            }
+            return this.updatePipeline(doUpdate);
         } catch (err) {
             this._logger.error('Error while removing bucket from connector', {
                 method: 'Connector.removeBucket',
@@ -274,11 +300,16 @@ class Connector {
 
     /**
      * Makes new connector pipeline that includes
-     * buckets assigned to this connector
+     * buckets assigned to this connector. If the
+     * singleChangeStream parameter is set to true,
+     * returns a pipeline that listens to all collections.
      * @param {string[]} buckets list of bucket names
      * @returns {string} new connector pipeline
      */
     _generateConnectorPipeline(buckets) {
+        if (this._singleChangeStream) {
+            return '[]';
+        }
         const pipeline = [
             {
                 $match: {