Error in connecting to document DB intermittently

Hi,

I am facing the below exception intermittently. I am using the connection as below.

“errorMessage”:“MongoTimeoutError: Server selection timed out after 30000 ms”,“reason”:{“errorType”:“MongoTimeoutError”,“errorMessage”:“Server selection timed out after 30000 ms”,“name”:“MongoTimeoutError”,“stack”:[“MongoTimeoutError: Server selection timed out after 30000 ms”," at Timeout.setTimeout [as _onTimeout] (/var/task/node_modules/mongodb/lib/core/sdam/server_selection.js:308:9)"," at ontimeout (timers.js:436:11)"," at tryOnTimeout (timers.js:300:5)"," at listOnTimeout (timers.js:263:5)"," at Timer.processTimers (timers.js:223:10)"]},“promise”:{},“stack”:[“Runtime.UnhandledPromiseRejection: MongoTimeoutError: Server selection timed out after 30000 ms”," at process.on (/var/runtime/index.js:37:15)"," at process.emit (events.js:198:13)"," at process.EventEmitter.emit (domain.js:448:20)"," at emitPromiseRejectionWarnings (internal/process/promises.js:140:18)"," at process._tickCallback (internal/process/next_tick.js:69:34)"]}

let connectionString = mongodb://${data.username}:${data.password}@${clusterEndpoint}:27017/?ssl=true&ssl_ca_certs=rds-combined-ca-bundle.pem&replicaSet=rs0;
return new Promise((resolve, reject) => {
mongodb.connect(connectionString, { useUnifiedTopology: true }, (err, res) => {
if (err) {
reject(err);
} else {
resolve(res);
}
})
});