feat(NODE-3607): update tcp keepalive options

Author: durran

src/cmap/connect.ts

@@ -333,10 +333,10 @@ function makeConnection(options: MakeConnectionOptions, _callback: Callback<Stre
   const noDelay = options.noDelay ?? true;
   const connectTimeoutMS = options.connectTimeoutMS ?? 30000;
   const rejectUnauthorized = options.rejectUnauthorized ?? true;
-  const keepAliveInitialDelay =
-    ((options.keepAliveInitialDelay ?? 120000) > socketTimeoutMS
-      ? Math.round(socketTimeoutMS / 2)
-      : options.keepAliveInitialDelay) ?? 120000;
+  // Default to delay to 300 seconds. Node automatically then sets TCP_KEEPINTVL to 1 second
+  // which is acceptable to the recommendation of 10 seconds and also cannot be configured.
+  // TCP_KEEPCNT is also set to 10 in Node and cannot be configured. (Recommendation is 9)
+  const keepAliveInitialDelay = options.keepAliveInitialDelay || 300000;
   const existingSocket = options.existingSocket;
 
   let socket: Stream;

src/cmap/connection.ts

@@ -122,7 +122,9 @@ export interface ConnectionOptions
   credentials?: MongoCredentials;
   connectTimeoutMS?: number;
   tls: boolean;
+  /** @deprecated - Will not be able to turn off in the future. */
   keepAlive?: boolean;
+  /** @deprecated - Will not be configurable in the future. */
   keepAliveInitialDelay?: number;
   noDelay?: boolean;
   socketTimeoutMS?: number;

src/connection_string.ts

@@ -864,12 +864,14 @@ export const OPTIONS = {
       return wc;
     }
   },
+  /** @deprecated - Will not be able to turn off in the future. */
   keepAlive: {
     default: true,
     type: 'boolean'
   },
+  /** @deprecated - Will not be configurable in the future. */
   keepAliveInitialDelay: {
-    default: 120000,
+    default: 300000,
     type: 'uint'
   },
   loadBalanced: {

src/mongo_client.ts

@@ -211,9 +211,12 @@ export interface MongoClientOptions extends BSONSerializeOptions, SupportedNodeC
   sslCRL?: string;
   /** TCP Connection no delay */
   noDelay?: boolean;
-  /** TCP Connection keep alive enabled */
+  /** @deprecated TCP Connection keep alive enabled. Will not be able to turn off in the future. */
   keepAlive?: boolean;
-  /** The number of milliseconds to wait before initiating keepAlive on the TCP socket */
+  /**
+   * @deprecated The number of milliseconds to wait before initiating keepAlive on the TCP socket.
+   *             Will not be configurable in the future.
+   */
   keepAliveInitialDelay?: number;
   /** Force server to assign `_id` values instead of driver */
   forceServerObjectId?: boolean;