Docs Menu
Docs Home
MongoDB Atlas

Troubleshoot Connection Issues

On this page

  • Cluster Connect button is disabled
  • Connecting IP address not in IP Access List
  • Authentication to the cluster failed
  • Too many open connections to your cluster
  • Degraded performance in sharded clusters during spikes in connection counts
  • Attempting to connect from behind a firewall
  • Cluster Availability
  • MongoDB Compass Troubleshooting
  • Connection String Issues

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 MongoDB Community Resources.


Serverless instances don't support connecting via certain drivers or driver versions at this time. To learn more, see Serverless Instance Limitations.

Your cluster's Connect button may be disabled if your cluster is in the provisioning state. Your cluster 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 cluster, check that you added your host's IP address to the IP access list for your cluster'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 cluster, 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 cluster.

  • 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 cluster. 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 cluster 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 can generate an optimized SRV connection string for sharded clusters using the load balancers from your private endpoint service. When you use an optimized connection string, Atlas limits the number of connections per mongos between your application and your sharded cluster. The limited connections per mongos improve performance during spikes in connection counts.


Atlas doesn't support optimized connection strings for clusters that run on Google Cloud or Azure.

To learn more about optimized connection strings for sharded clusters behind a private endpoint, see Improve Connection Performance for Sharded Clusters Behind a Private Endpoint.

Atlas uses a CDN to serve content quickly. If your organization uses a firewall, add the following Atlas CDN host to the firewall's allow list to prevent issues accessing the Atlas UI:

Atlas clusters operate on port 27017. You must be able to reach this port to connect to your clusters. 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.


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 cluster, the cluster might be paused or deleted. Check that the cluster 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 and experience issues, see:

If you use a self-managed X.509 certificate or an auto-generated X.509 certificate managed by Atlas to authenticate to the MongoDB database, when you connect to MongoDB Compass, you must:

  1. In MongoDB Compass, choose Fill in connection fields individually.

  2. In the Authentication dropdown, select X.509.

  3. Select More Options.

  4. In the SSL dropdown, select Server and Client Validation.

  5. Add the same path to the downloaded Atlas-managed certificate, or the self-managed certificate (depending on which you use) to each of these fields: Certificate Authority, Client Certificate, and Client Private Key.

To learn more, see Connect to MongoDB in the MongoDB Compass documentation.

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 your password includes special characters, and you are using your password in a connection string URI, encode the special characters.

If you try to update a password with a special character that requires percent encoding, the following error message appears:

This password contains special characters which will be URL-encoded.


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

: / ? # [ ] @ ! $ & ' ( ) * , ; = %

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


Use the Select your language drop-down menu to set the language of the encoding example in this section.

1package main
3import (
4 "context"
5 "fmt"
6 "net/url"
8 ""
9 ""
10 ""
13func main() {
14 username := "<username>"
15 password := "<password>"
16 cluster := "<clusterName>"
17 authSource := "<authSource>"
18 authMechanism := "<authMechanism>"
20 uri := "mongodb+srv://" + url.QueryEscape(username) + ":" +
21 url.QueryEscape(password) + "@" + cluster +
22 "/?authSource=" + authSource +
23 "&authMechanism=" + authMechanism
25 client, err := mongo.Connect(context.TODO(), options.Client().ApplyURI(uri))
26 if err != nil {
27 panic(err)
28 }
29 defer client.Disconnect(context.TODO())
31 collection := client.Database("<dbName>").Collection("<collName>")
33 cursor, err := collection.Find(context.TODO(), bson.D{})
34 if err != nil {
35 panic(err)
36 }
38 var results []bson.D
39 if err = cursor.All(context.TODO(), &results); err != nil {
40 panic(err)
41 }
42 for _, result := range results {
43 fmt.Println(result)
44 }
1import com.mongodb.client.MongoClient;
2import com.mongodb.client.MongoClients;
3import com.mongodb.client.MongoCollection;
4import com.mongodb.client.MongoDatabase;
6import org.bson.Document;
9public class Encoding {
11 public static void main(String [] args){
13 try{
14 String username = URLEncoder.encode("<username>", "UTF-8");
15 String password = URLEncoder.encode("<password>", "UTF-8");
16 String cluster = "<clusterName>";
17 String authSource = "<authSource>";
18 String authMechanism = "<authMechanism>";
20 String uri = "mongodb+srv://" + username + ":" + password + "@" + cluster +
21 "/?authSource=" + authSource + "&authMechanism=" + authMechanism;
23 MongoClient mongoClient = MongoClients.create(uri);
25 MongoDatabase database = mongoClient.getDatabase("<dbName>");
26 MongoCollection<Document> collection = database.getCollection("<collName>");
28 collection.find().forEach(doc -> System.out.println(doc.toJson()));
30 } catch(Exception e){
31 System.err.println(e.getCause());
33 }
34 }
1const { MongoClient } = require("mongodb");
3const username = encodeURIComponent("<username>");
4const password = encodeURIComponent("<password>");
5const cluster = "<clusterName>";
6const authSource = "<authSource>";
7const authMechanism = "<authMechanism>";
9let uri =
10 `mongodb+srv://${username}:${password}@${cluster}/?authSource=${authSource}&authMechanism=${authMechanism}`;
12const client = new MongoClient(uri);
14async function run() {
15 try {
16 await client.connect();
18 const database = client.db("<dbName>");
19 const ratings = database.collection("<collName>");
21 const cursor = ratings.find();
23 await cursor.forEach(doc => console.dir(doc));
24 } finally {
25 await client.close();
26 }
1import pymongo
2from urllib.parse import quote_plus
4username = quote_plus('<username>')
5password = quote_plus('<password>')
6cluster = '<clusterName>'
7authSource = '<authSource>'
8authMechanism = '<authMechanism>'
10uri = 'mongodb+srv://' + username + ':' + password + '@' + cluster + '/?authSource=' + authSource + '&authMechanism=' + authMechanism
12client = pymongo.MongoClient(uri)
14result = client["<dbName"]["<collName>"].find()
16# print results
17for i in result:
18 print(i)


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).

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 cluster.

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, select an older version of the driver or Compass to use the Standard Connection String format. With Compass, don't set the SRV Record value, set the Hostname and Port values instead.


Google Cloud


Configure Security Features