Hello!

In this video, we’ll discuss how to troubleshoot common connection issues when trying to connect to MongoDB Atlas by using a Java driver.

Before we begin, it’s important to remember that it’s common to experience connectivity issues when learning how to connect your application to MongoDB.

Connectivity issues may stem from systems put in place to protect our database, like IP access restrictions. MongoDB has a lot of resources to help you understand and address these issues.

Let’s examine a few examples of connection issues that you may experience.

First, when your application connects to an Atlas cluster, the connecting application’s host IP address must be configured in Atlas.

If the host is not included in the Atlas clusters’ IP Access List, the driver reports an error that it cannot connect.

To see this in action, let’s navigate to the Network Access panel and delete all of the allowed IP addresses. The Network Access panel will now be empty, like this:

Now, use a terminal session on the application’s host IP to connect to your cluster. It will return a connection error.

To fix the issue, navigate back to the Network Access panel and add your current IP address.

Now try connecting again in the terminal. The standard output will look like this:

Congratulations! You fixed a common connection error caused by incorrect configuration on the IP Access List.

Another common connection issue is caused by an invalid connection string format.

The Atlas connection string that we specify within our application must be a valid MongoDB connection URI.

If the connection URI contains embedded credentials that use any of the characters shown here, we must percent-encode the credential characters to get a valid URI.

For example, if a password is this , the percent-encoded equivalent would be this .

An incorrect username and/or password will result in authentication errors.

Common causes of this type of error are

unencoded special characters in the password or undefined users in the default admin database.

If users are defined in a different database, then the authSource parameter must be included in the connection string URI.

Another potential source of errors is firewall misconfiguration.

By default, MongoDB listens on port 27017. If your firewall restricts access to this port, then you won't be able to connect to your MongoDB cluster or instance. This can be resolved by opening port 27017 on your firewall.

Errors can also result from too many open connections. Atlas sets limits for concurrent incoming connections to a database deployment. The limit is dependent on the cluster tier.

If you try to connect when you are at this limit, MongoDB will display an error stating that the connection was refused because there are too many open connections.

To resolve this, you can try: Restarting your application, closing any open connections to your database that are not currently in use, scaling your cluster to a higher tier to support more connections, or limiting the number of connections in the connection pool by using the maxPoolSize connection string option.

Applications that fail to close unused connections allow open connections to pile up and eventually exceed the connection limit. To avoid this issue, make sure that your Java application calls the MongoClient.close() method.

Well done!

In this video, you learned how to troubleshoot some of the most common issues when connecting to a MongoDB Atlas cluster. These include: Atlas IP access restrictions, invalid connection string format, incorrect authentication, fiirewall misconfiguration, and unclosed connections.

All of these issues can result in errors when trying to connect to MongoDB from your application.