Number of active connections on the server reached

Question

I am working with mongodb and nodejs. I have mongodb hosted on Atlas.

My backend had been working perfectly but now it is sometimes getting stuck and when I see the analytics on mongodb atlas it shows maximum number of active connections reached to 100.

Can someone please explain why this is happening? Can I reboot the connections and make it 0?

@Stennie I have used mongoose to connect to database

Here is my configuration file

const mongooseOptions = {
  useNewUrlParser: true,
  autoReconnect: true,
  poolSize: 25,
  connectTimeoutMS: 30000,
  socketTimeoutMS: 30000
} 

exports.register = (server, options, next) => {
  defaults = Hoek.applyToDefaults(defaults, options)

  if (Mongoose.connection.readyState) {
    return next()
  }

  if (!Mongoose.connection.readyState) {
    server.log(`${process.env.NOED_ENV} server connecting to ${defaults.url} ${defaults.url}`)

    return Mongoose.connect(defaults.url, mongooseOptions).then(() => {
      return next() // call the next item in hapi bootstrap
    })
  }
}