useUnifiedTopology: true causes ECONNREFUSED.

[skavan]

Hi,

Bit of a mongo newbie, so forgive me if I use the wrong descriptive language.

"mongodb": "^3.6.4",
"mongoose": "^5.11.15",
 node: 14.15.4

Brand new install of mongoDB on a windows machine (A) with a db and collections.
It works fine...and a webapp (not mine) that displays data from the db , on this same machine (A) also works well...and proves that all is well on the mongoDB end.

But, I have a development machine (B) where I am writing a node app to access the data on Machine A (it is on the same segment). I am running into a strange problem.

Up until yesterday, it was working fine. I could happily access mongo on Machine A from node on Machine B (with useUnifiedTopology=true

But then, I decided to migrate my mongoDB to a one-node replicaSet to take advantage of the "watch" function. The process seems to have worked on the mongodb side. That webapp I referenced above is happily working, as is Compass. I see the oplog.rs and replset.* entries on the mongoDB instance.

But on my remote development machine (B), I can no longer connect to mongoDB on machine A, UNLESS I set useUnifiedTopology to false. When set to false, everything works (with the deprecation warning). That includes the collection.watch().on functionality. So the replication set seems to be working.

But when useUnifiedTopology=true, I get a DB connection error: MongooseServerSelectionError: connect ECONNREFUSED 127.0.0.1:27017.

BTW Compass works fine on the development machine.

My barebones code is below. I have tried a million variants, like wrapping the connection in an await - but all to no avail. What am I missing? Or is it a bug?

import mongoose from "mongoose";

const url = "mongodb://192.168.1.xxx:27017/MyDbName";

var options = {
  keepAlive: true,
  useNewUrlParser: true,
  useUnifiedTopology: false,
  connectWithNoPrimary: true
}

mongoose.connect(url, options);  

var db = mongoose.connection;

db.on("error", console.error.bind(console, "DB connection error:"));

db.once("open", function () {
  console.log("DB connection successful");
});

[skavan]

Of course, after hours and hours of searching, I just found the solution in another issue.
Hopefully it will help others: #9836 (comment)
append ?directConnection=true to the url.
Still feels like a bug or at least a doc change to me -- but what do I know.

[vkarpov15]

This sounds like an issue with replica set host names: https://mongoosejs.com/docs/connections.html#replicaset-hostnames . Typically this issue is because the machine running MongoDB has a hostname that is something the client can't reach.

directConnection=true means you aren't connecting to a replica set, you're connecting directly to one mongod server. Which may be fine for your use case, but defeats the point of having a replica set.