MongoDB Atlas Too Many Connections Error

How to fix it

Try these in order — the most common fix is first.

1. 1. Reuse the client

   1. Create the MongoClient once outside the request handler and cache it across invocations
   Did this fix it? Yes No

2. 2. Limit the pool

   Copy steps
   1. Set maxPoolSize in the connection string, e.g. ?maxPoolSize=10
   2. Close unused connections and restart the app
   Did this fix it? Yes No

3. 3. Scale the cluster

   1. Edit Configuration and pick a larger tier with a higher connection limit
   Did this fix it? Yes No

Symptoms

'connection refused because too many open connections', spikes in the Connections chart, serverless functions timing out.

Why it happens

• New MongoClient created per request (serverless)
• Large connection pool across many instances
• Tier connection limit reached

This guide also covers

• mongodb atlas too many connections
• connection refused because too many open connections
• mongodb atlas connection limit

The same problem in other apps

All not loading, error messages & connection guides →

• Supabase Max Client Connections Reached (Supabase)
• Firebase auth/invalid-api-key Error (Firebase)

Other MongoDB Atlas errors

• MongoDB Atlas Connection Timed Out (IP Not Whitelisted)
• MongoServerSelectionError: Fix for MongoDB Atlas
• MongoDB Atlas Authentication Failed (bad auth)
• MongoDB querySrv ENOTFOUND / ECONNREFUSED Error
• MongoDB Atlas Free Tier (M0) Limits and Throttling
• MongoDB Atlas Cluster Paused (Resume or Auto-Pause)
• MongoDB Atlas Unexpected Bill: Why It's So High
• MongoDB Atlas AWS VPC Peering Not Connecting