Docs Menu

Troubleshoot Connection Issues

On this page

This page outlines common connection issues and possible resolutions.

To learn more about connecting to an Atlas cluster, see the Get Started with Atlas tutorial.


If you are an enterprise customer looking for support, file a ticket. For community support, visit Community Support Resouces.

Serverless Instances are in Preview

Serverless instances are in preview and do not support connecting via certain drivers or driver versions at this time. To learn more, see Serverless Instance Limitations.

Your database deployment's Connect button may be disabled if your database deployment is in the provisioning state. Your database deployment needs to provision when it is first deployed. Clusters also must provision when you scaled them up or down. The provisoning process can take up to 10 minutes, after which the Connect button will become enabled.

Before connecting to your Atlas database deployment, check that you added your host's IP address to the IP access list for your database deployment's project. Atlas allows client connections only from IP addresses and CIDR address ranges in the IP access list.

To connect to Atlas, you must authenticate with a MongoDB database user. To create a database user for your database deployment, see Configure Database Users.

If you have created a user and are having trouble authenticating, try the following:

  • Check that you are using the correct username and password for your database user, and that you are connecting to the correct database deployment.
  • Check that you are specifying the correct authSource database in your connection string.
  • If you have a special character in your password, see Special characters in connection string password.

Atlas sets limits for concurrent incoming connections to a database deployment. For clusters, this is based on the cluster tier. If you try to connect when you are at this limit, MongoDB displays an error stating connection refused because too many open connections.

For a detailed comparision of cluster tiers and their maximum concurrent connections, see Connection Limits and Cluster Tier.

  • Close any open connections to your database deployment not currently in use.
  • Scale your cluster to a higher tier to support more concurrent connections.
  • Restart your application.
  • To prevent this issue in the future, consider using the maxPoolSize connection string option to limit the number of connections in the connection pool.

To learn how to fix this issue, see Fix Connection Issues.

Atlas database deployments operate on port 27017. You must be able to reach this port to connect to your database deployments. Additionally, ensure that the appropriate ports are open for the following:

  • For sharded clusters, grant access to port 27016.
  • For BI Connector, grant access to port 27015.

You can check your ability to reach a port using the third-party Outgoing port tester.


To check your ability to reach port 27017, visit

If you can't access these ports, check your system firewall settings and ensure that they are not blocking access to these ports.

If you are using a mongodb+srv:// connection string and your driver or shell can't find the DNS host of the Atlas database deployment, the database deployment might be paused or deleted. Check that the database deployment exists. If this is a paused cluster, you can resume the cluster if necessary.


Atlas automatically pauses idle M0 clusters after 60 days with no connections.

If you use MongoDB Compass to connect to your cluster, refer to the Compass Connection Errors for additional resources.

See also: Connection Refused using SRV Connection String

The connection string format you use to connect to Atlas depends on several factors, including:

Verify your connection string in a test environment before putting it into production.

If you have special characters in your password, you must encode those characters if using your password in a connection string URI.


The following characters must be converted using percent encoding if included in a username or password:

: / ? # [ ] @

If your password in plain-text is p@ssw0rd'9'!, you would need to encode your password as:


Do not encode special characters in your password if you are using your password outside of a connection string URI (for example, pasting it into mongosh or MongoDB Compass).

If you see this error message, your driver is likely out of date. For instructions on updating your driver, refer to your specific Driver Documentation.

When you use the DNS seed list connection string format to connect to Atlas, you might see the following error:

DNSHostNotFound: Failed to look up service “<MongoDB service name>”

This error may occur when using the default DNS server that your ISP provides. That DNS server might not support SRV lookups that the DNS seed list connection string format uses.

To resolve the issue, you can try changing your DNS configuration to use a public DNS server.


You can configure your network settings to use Google Public DNS instead of your ISP's DNS servers.

After you update your network settings to use a public DNS server, connect to the database deployment.

If running Ubuntu 18.04 and using the DNS seed list connection string format (mongodb+srv://) to connect to Atlas from one of the MongoDB Database Tools (mongodump, mongorestore, etc), you might see the following error:

lookup on cannot unmarshal DNS message

If so, use one of the following connection options instead:

When using the DNS seed list connection string format (mongodb+srv://) with a driver or Compass, you may receive in the following error:

Error: querySrv ECONNREFUSED _mongodb._tcp.<SRV Record>

To remedy this issue, use the Standard Connection String format with Compass or that driver. With Compass, don't set the SRV Record value, set the Hostname and Port values instead.

Give Feedback
MongoDB logo
© 2021 MongoDB, Inc.


  • Careers
  • Legal Notices
  • Privacy Notices
  • Security Information
  • Trust Center
© 2021 MongoDB, Inc.