"MongoError: server selection failed" after upgrading from 5.9.19 to 5.9.20

[amit777]

Do you want to request a feature or report a bug?
bug

What is the current behavior?
My app crashed with this stack trace:

    at Mongos.selectServer (/opt/app/backend/node_modules/mongodb/lib/core/topologies/mongos.js:1176:14)
    at Mongos.selectServer (/opt/app/backend/node_modules/mongodb/lib/topologies/topology_base.js:342:32)
    at executeWithServerSelection (/opt/app/backend/node_modules/mongodb/lib/operations/execute_operation.js:137:12)
    at executeOperation (/opt/app/backend/node_modules/mongodb/lib/operations/execute_operation.js:75:7)
    at Cursor._initializeCursor (/opt/app/backend/node_modules/mongodb/lib/core/cursor.js:540:7)
    at Cursor._initializeCursor (/opt/app/backend/node_modules/mongodb/lib/cursor.js:185:11)
    at nextFunction (/opt/app/backend/node_modules/mongodb/lib/core/cursor.js:743:10)
    at Cursor._next (/opt/app/backend/node_modules/mongodb/lib/core/cursor.js:201:5)
    at Cursor._read (/opt/app/backend/node_modules/mongodb/lib/core/cursor.js:340:10)
    at Cursor.Readable.read (_stream_readable.js:468:10)    at resume_ (_stream_readable.js:982:12)
    at processTicksAndRejections (internal/process/task_queues.js:84:21)

If the current behavior is a bug, please provide the steps to reproduce.

I'm still investigating why this would happen since other apps we created are working fine after the upgrade.

What is the expected behavior?
There should be no error connecting.

What are the versions of Node.js, Mongoose and MongoDB you are using? Note that "latest" is not a version.

5.9.20

Other environment notes:

• MongoDB 4.2.7 sharded cluster
• Node v12.18.1
• My app is connecting to mongos connected on localhost:27018
• Downgrading mongoose seems to fix the problem reliably.

[amit777]

Here are my connection options:

"db": "mongodb://localhost:27018/app"
      
"dbOptions": {
        "native_parser": true,
        "poolSize": 10
      }

[amit777]

In one of my modules i'm calling mongoose.connect(). I think we are calling this multiple times in different parts of the code.

[und3rs]

I'm on simillar situation.
After updating mongoose from 5.9.19 to 5.9.20, mongoose cannot connect to mongoDB.
Obviously, every thing is OK if I just do downgrade mongoose to 5.9.19.

• MongoDB 4.2 sharded cluster
• Multiple MONGOS like this. (mongodb://host1,host2,host3)

[vkarpov15]

Thanks for reporting, will investigate and see if we can repro this issue on a multi-mongos setup.

[amit777]

I was able to fix my issue by removing some extraneous connect code in one of my models

[vkarpov15]

I haven't been able to repro this, but this comment makes it highly probable that this issue is due to the fix for #9107 . We'll revert those changes.