Mongoose opening too many Mongodb connections - node.js

Question

I am new to mongoose/mongodb and would like some help on making database connections. I am observing that my express/next app is opening too many connections causing an alert on my Atlas hosted MongoDB.
I am making connections using mongoose(version 5.12.3) in a pretty standard way. Haven't defined any pool size (understand mongoose standard is 5) or timeout related issues. The connection is made twice - once for the application queries and second as a part of Mongo session store. I am just running 5 such node servers.
What I observed is - after reaching threshold, I killed each node server, one at a time. Still my atlas was showing some 23 connections. So I completely removed the network access to my node server and yet it took a while to come to zero. Then I started 2 of my node processes and I suddenly saw number of connections jumping to 60. As I do more and more activities on my node server, I just see this count ever increasing. And sometimes, without good reason, it shows a sudden dip. Also it's not that I have time consuming queries. Although I haven't measured time, generally the client side result is shown within a flash of a second. I am also not closing the connection on SIGTERM/SIGKILL.
I have following specific questions:
What are the recommended connection parameters for production usage?
Should I be closing connection on SIGTERM/SIGKILL?
What is the reason, for my 5 node processes, Atlas now shows about 70+ connections? The number varies with time - possibly correlated to user actions.
Is it that the number just kept on adding upon each bounce/restart of my node server and hence one fine day it reached threshold?
Below is code I use:
To create mongoose connection for queries:
mongoose.connect(process.env.INRMONGODB,
{useNewUrlParser: true, useUnifiedTopology: true, useFindAndModify: false, useCreateIndex: true},
(err) => {
if (err) {
console.log(err, "MONGODB CONNECTION ERROR");
return false;
}
console.log("Mongoose Is Connected");
}
);
As a part of sessionStore:
app.use(session({
secret: process.env.SESSION_SECRET,
saveUninitialized: false,
resave: false,
rolling: false,
name: process.env.COOKIENAME,
cookie: sessionCookieOptions,
store: new MongoStore({
uri: process.env.INRMONGODB, ttl: 2000, autoRemove: 'interval', autoRemoveInterval: 20, // In minutes
hash: {
salt: process.env.SALTSECRET,
algorithm: 'sha1'
}
})
}));
I also tried adding mongoose connection event handlers to see if anywhere any disconnection is happening - but that is not the case. Please guide.

Answer 1

Well, I would use the existing connection for the MongoStore.
mongoose.connect(process.env.MONGO_CONNECTION_URL, { useNewUrlParser: true, useCreateIndex:true, useUnifiedTopology: true, useFindAndModify : true });
const connection = mongoose.connection;
connection.once('open', () => {
console.log('Database connected...');
}).catch(err => {
console.log('Connection failed...')
});
// Session store
let mongoStore = new MongoDbStore({
mongooseConnection: connection,
collection: 'sessions'
})
You might have look at my project where, I have used these things.
Project source code