Mongoose too many connection and commands - node.js

Question

I'm here to request help with mongo/mongoose. I use AWS lambda that accesses a mongo database and I'm having problems sometimes my connections reach the limit of 500. I'm trying to fix this problem and I did some things like this https://dzone.com/articles/how-to-use-mongodb-connection-pooling-on-aws-lambd and https://www.mongodb.com/blog/post/optimizing-aws-lambda-performance-with-mongodb-atlas-and-nodejs. That basically is to use a singleton-like and set context.callbackWaitsForEmptyEventLoop = false, which indeed helped but is still, rarely, open 100 connections in less than a minute, it looks like there is some connection that is not being reused even tho our logs show that they are being reused. So I realized a weird behavior, whenever mongoatlas shows me an increased number of commands, my mongo connections increase heavily. The first chart is operations and the second is the connections.
Looking at operations, there are too many commands and just a few queries. I have no idea what are those commands, my theory is that those commands are causing the problem but I did not find anything that explained what is the difference between query and command exactly for me to know if that is a valid theory or not. Another thing is, how to choose correctly the number of pool size, we have really simple queries.
Here is our singleton class because maybe this is what we are doing wrong:
class Database {
options: [string, mongoose.ConnectionOptions];
instance?: typeof mongoose | null;
constructor(options = config) {
console.log('[DatabaseService] Created database instance...');
this.options = options;
this.instance = null;
}
async checkConnection() {
try {
if (this.instance) {
const pingResponse = await this.instance.connection.db.admin().ping();
console.log(`[DatabaseService] Connection status: ${pingResponse.ok}`);
return pingResponse.ok === 1;
}
return false;
} catch (error) {
console.log(error);
return false;
}
}
async init() {
const connectionActive = await this.checkConnection();
if (connectionActive) {
console.log(`[DatabaseService] Already connected, returning instance`);
return this.instance;
}
console.log('[DatabaseService] Previous connection was not active, creating new connection...');
this.instance = await mongoose.connect(...this.options);
const timeId = Date.now();
console.log(`Connection opened ${timeId}`);
console.time(`Connection started at ${timeId}`);
this.instance?.connection.on('close', () => {
console.timeEnd(`Connection started at ${timeId}`);
console.log(`Closing connection ${timeId}`);
});
return this.instance;
}
async getData(id: string) {
await this.init();
const response = await Model.findOne({ 'uuid': id });
return response;
}
}
I hope that is enough information. My main question is if my theory of commands causing too many connections is possible and what are exactly commands because every explanation that I found look like is the same than query.

Answer 1

Based on the comment written by Matt I have changed my init function and now my connections are under control.
async init() {
if (this.instance) {
console.log(`[DatabaseService] Already connected, returning instance`);
return this.instance;
}
console.log('[DatabaseService] Previous connection was not active, creating new connection...');
this.instance = await mongoose.connect(...this.options);
const timeId = Date.now();
console.log(`Connection opened ${timeId}`);
console.time(`Connection started at ${timeId}`);
this.instance?.connection.on('close', () => {
console.timeEnd(`Connection started at ${timeId}`);
console.log(`Closing connection ${timeId}`);
});
return this.instance;
}