Inconsistent MongoServerSelectionError: Server selection timed out after 30000 ms

Gonzalo_Hirsch · 2021-12-16T14:40:22.828Z

We have an API working with MongoDB Atlas, connection works 99% of the time, but we occasionally get a MongoServerSelectionError: Server selection timed out after 30000 ms on a specific endpoint for some reason. Like I said, it fails 2/3 times out of 100.

We are connecting like so:

const { MongoClient} = require('mongodb');
const client = new MongoClient(
  process.env.MONGODB_CONNECTION_STRING,
  {
    useNewUrlParser: true,
    useUnifiedTopology: true
  }
);
module.exports = client.connect();

This is running on Netlify Functions, and whenever the function needs to use Mongo, it just awaits the connection promise.

Full error:

{
   "errorType":"Runtime.UnhandledPromiseRejection",
   "errorMessage":"MongoServerSelectionError: Server selection timed out after 30000 ms",
   "reason":{
      "errorType":"MongoServerSelectionError",
      "errorMessage":"Server selection timed out after 30000 ms",
      "reason":{
         "type":"ReplicaSetNoPrimary",
         "servers":{
            
         },
         "stale":false,
         "compatible":true,
         "heartbeatFrequencyMS":10000,
         "localThresholdMS":15,
         "setName":"atlas-13tibr-shard-0"
      },
      "stack":[
         "MongoServerSelectionError: Server selection timed out after 30000 ms",
         "    at Timeout._onTimeout (/var/task/node_modules/mongodb/lib/sdam/topology.js:330:38)",
         "    at listOnTimeout (internal/timers.js:557:17)",
         "    at processTimers (internal/timers.js:500:7)"
      ]
   },
   "promise":{
      
   },
   "stack":[
      "Runtime.UnhandledPromiseRejection: MongoServerSelectionError: Server selection timed out after 30000 ms",
      "    at process.<anonymous> (/var/runtime/index.js:35:15)",
      "    at process.emit (events.js:400:28)",
      "    at processPromiseRejections (internal/process/promises.js:245:33)",
      "    at processTicksAndRejections (internal/process/task_queues.js:96:32)"
   ]
}

Alfonso · 2022-01-17T00:52:25.543Z

We have the exact same issue. Were you able to resolve it?

What’s really annoying is this didn’t happen to us in the free tier. It only started happening in the paid tier

Ben_Hason · 2023-01-31T22:51:36.436Z

Did you manage to solve it somehow?

nathaniel_redmon · 2023-03-22T04:21:27.606Z

This is a serious issue for our small startup. We are hosting on Vercel and are seeing roughly the same failure rates.

Has anyone solved this? We need this fixed ASAP

Kevin_Schmidt · 2023-07-03T11:36:11.228Z

Any solution to this?

Frank_Apap · 2023-12-17T21:05:06.004Z

Anyone on this thread happen to ever find a solution?

Curious for those having this issue, are you using app or pages router?

Durran_Jordan · 2023-12-20T16:38:44.214Z

From the original error, the topology is of type ReplcaSetNoPrimary, which would indicate some sort of network connection issue between the driver and the primary node and a write was taking place when this happened or the use or the default read preference or “primary” was being used with a read. To debug this better one can add a listener on the server monitors to see if an error occurred:

const client = new MongoClient(process.env.MONGODB_URI);
client.on('serverHeartbeatFailed', (event) => {
  console.log(event);
});

Note:
What type of operation is being executed when the error occurs? If it’s a write, the primary must be available, if it’s a read, check the read preference and consider if using “primary” to change it to something like “primaryPreferred”, “secondaryPreferred”, or “secondary”.

Frank_Apap · 2023-12-20T18:25:02.710Z

It happens for me on both reads and rights. What is really odd is that I have instrumented my code heavily with log output all over the place. When this error occurs NONE of the logging happens. It’s almost as if request A creates a connection, responds. Then that connection, while pooled, has an issue, but nothing consumes the exception. Then when request B comes in and gets assigned to the thread it blows up before running ANY of my actual code. No idea if this is the case but that is what it appears to be.

Also for whatever it’s worth - there is a thread looking at this from the Vercel perspective:

github.com/vercel/vercel

MongoDB Integration causes intermittent connection errors (LAMBDA_RUNTIME fails)

opened 07:51AM - 06 Oct 23 UTC

Nikhil22

### Discussed in https://github.com/vercel/vercel/discussions/10621 <div type…='discussions-op-text'> <sup>Originally posted by **Nikhil22** September 28, 2023</sup> ### Question When I connect to MongoDB (via MONGODB_URI env variable, via the node driver) from my Vercel-deployed app, I get intermittent errors (MongoServerSelectionError) that present as 500 errors in my Vercel-deployed app. The errors go away on refresh. An example of the error is: ``` ERROR Unhandled Promise Rejection { "errorType":"Runtime.UnhandledPromiseRejection", "errorMessage":"MongoServerSelectionError: Server selection timed out after 30000 ms", "reason":{ "errorType":"MongoServerSelectionError", "errorMessage":"Server selection timed out after 30000 ms", "reason":{ "type":"ReplicaSetNoPrimary", "servers":{ }, "stale":false, "compatible":true, "heartbeatFrequencyMS":10000, "localThresholdMS":15, "setName":"atlas-j7739j-shard-0", "maxElectionId":null, "maxSetVersion":null, "commonWireVersion":0, "logicalSessionTimeoutMinutes":null }, "stack":[ "MongoServerSelectionError: Server selection timed out after 30000 ms", " at Timeout._onTimeout (/var/task/node_modules/mongodb/lib/sdam/topology.js:278:38)", " at listOnTimeout (node:internal/timers:569:17)", " at process.processTimers (node:internal/timers:512:7)" ] }, "promise":{ }, "stack":[ "Runtime.UnhandledPromiseRejection: MongoServerSelectionError: Server selection timed out after 30000 ms", " at process.<anonymous> (file:///var/runtime/index.mjs:1250:17)", " at process.emit (node:events:526:35)", " at emit (node:internal/process/promises:149:20)", " at processPromiseRejections (node:internal/process/promises:283:27)", " at process.processTicksAndRejections (node:internal/process/task_queues:96:32)" ] } "LAMBDA_RUNTIME Failed to post handler success response. Http response code":"400. ``` Just to be clear, the connection string and credentials *work and are correct* as it does connect properly when errors are not there, but when errors that I describe above do occur, it crashes the entire app. I've written about this in detail in the MongoDB community here (https://www.mongodb.com/community/forums/t/no-way-to-avoid-replicasetnoprimary-errors/243498). I've also been in contact with MongoDB support and they said that there are no problems with the Mongo cluster itself. Moreover, upon further research, it seems that this is a common problem when trying to connect to MongoDB from Vercel. For example, here (https://www.mongodb.com/community/forums/t/intermittently-getting-mongoserverselectionerror-error-on-my-next-js-vercel-deployment/242470). I'd like to solve this problem, or at the very least, not have my entire app crash with a 500 due to the error, as it currently does. Please help.</div>

Durran_Jordan · 2023-12-20T21:02:55.783Z

What version of the driver are you using?

Frank_Apap · 2023-12-20T22:12:24.743Z

I’m using 5.9.1, in the latest version of my code I see that when the issue occurs the “serverClosed” event runs at basically the same time (or at least outputs it logs).

Frank_Apap · 2023-12-22T13:37:20.299Z

So I think my theory is correct. I just had an example where a request that does not even use the database errors out with the following logs associated with it:

serverHeartbeat issue (might not be an error): {"connectionId":"ac-mxrxhwn-shard-00-02.ss9fyeo.mongodb.net:27017","duration":318996,"failure":{}}
serverClosed! ServerClosedEvent {
  topologyId: 0,
  address: 'ac-mxrxhwn-shard-00-02.ss9fyeo.mongodb.net:27017'
}
serverHeartbeat issue (might not be an error): {"connectionId":"ac-mxrxhwn-shard-00-00.ss9fyeo.mongodb.net:27017","duration":318982,"failure":{}}
serverClosed! ServerClosedEvent {
  topologyId: 0,
  address: 'ac-mxrxhwn-shard-00-00.ss9fyeo.mongodb.net:27017'
}
serverHeartbeat issue (might not be an error): {"connectionId":"ac-mxrxhwn-shard-00-01.ss9fyeo.mongodb.net:27017","duration":318981,"failure":{}}
serverClosed! ServerClosedEvent {
  topologyId: 0,
  address: 'ac-mxrxhwn-shard-00-01.ss9fyeo.mongodb.net:27017'
}
Unhandled Promise Rejection 	{"errorType":"Runtime.UnhandledPromiseRejection","errorMessage":"MongoServerSelectionError: Server selection timed out after 10000 ms","reason":{"errorType":"MongoServerSelectionError","errorMessage":"Server selection timed out after 10000 ms","reason":{"type":"ReplicaSetNoPrimary","servers":{},"stale":false,"compatible":true,"heartbeatFrequencyMS":10000,"localThresholdMS":15,"setName":"atlas-1327c9-shard-0","maxElectionId":null,"maxSetVersion":null,"commonWireVersion":0,"logicalSessionTimeoutMinutes":null},"stack":["MongoServerSelectionError: Server selection timed out after 10000 ms","    at Timeout._onTimeout (/var/task/node_modules/mongodb/lib/sdam/topology.js:278:38)","    at listOnTimeout (node:internal/timers:569:17)","    at process.processTimers (node:internal/timers:512:7)"]},"promise":{},"stack":["Runtime.UnhandledPromiseRejection: MongoServerSelectionError: Server selection timed out after 10000 ms","    at process.<anonymous> (file:///var/runtime/index.mjs:1276:17)","    at process.emit (node:events:529:35)","    at emit (node:internal/process/promises:149:20)","    at processPromiseRejections (node:internal/process/promises:283:27)","    at processTicksAndRejections (node:internal/process/task_queues:96:32)","    at runNextTicks (node:internal/process/task_queues:64:3)","    at process.processTimers (node:internal/timers:509:9)"]}
Error: Runtime exited without providing a reason

Willis_Chou1 · 2024-04-21T10:51:15.909Z

Hey, I am facing the same issue. I can’t find any solution and mongodb support suggests me find something here