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Struggling to connect your ASP.NET Core application to MongoDB Atlas? Discover how to solve the 'No connection could be made because the target machine actively refused it' error with our step-by-step guide.
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This video is based on the question https://stackoverflow.com/q/63656860/ asked by the user 'Nikita Fedorov' ( https://stackoverflow.com/u/6188783/ ) and on the answer https://stackoverflow.com/a/63660197/ provided by the user 'Joe' ( https://stackoverflow.com/u/2282634/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Resolve MongoDB Connection Issues in ASP.NET Core: Active Refusal Error Explained

Connecting your ASP.NET Core application to a MongoDB Atlas cluster can sometimes lead to frustrating errors. One such error is “No connection could be made because the target machine actively refused it.” In this post, we will unpack what this error means and provide you with a structured solution to resolve it effectively.

Understanding the Error

When you attempt to connect to your MongoDB Atlas and face the above-mentioned error, it essentially indicates that the target machine (in this case, your MongoDB instance) has received your request but isn't allowing the connection on the defined port. This usually implies one of the following scenarios:

The MongoDB server is not running.

There is no service listening on the specified port.

There is a DNS issue causing misrouting of your connection.

Detailed Insights

When you see an error message that references a port (for example, <my_ip>:53), it's crucial to understand what that port is associated with:

Port 53 is typically used for DNS requests. If your application is trying to use this port, it's likely misconfigured regarding DNS resolution.

Diagnosing the Problem

To successfully diagnose the problem, we need to analyze a few key components:

1. Checking if the Target IP is Listening

Ensure that the IP address identified in the error message refers to your MongoDB Atlas instance and that the database is up and running.

Use tools like ping or telnet on the MongoDB server to confirm if the server is reachable and listening on the required port.

2. Local Environment Configuration

If you are not running a DNS server yet still see <my_ip>:53 in the error, examine your ASP.NET application’s configuration to see why it is using that particular IP for DNS resolution.

Check your network settings in your operating system to ensure no DNS hijacking or misconfiguration is happening.

Potential Solutions

Here are some steps to resolve the connection failure effectively:

1. Whitelist Your IP Address Correctly

Double-check your MongoDB Atlas security settings. Even if you believe you've whitelisted your IP, ensure that the IP you're executing tests from is actually included and correctly set in the MongoDB Atlas dashboard.

2. Change Your Connection String

Instead of using SRV URLs (mongodb+ srv://), try using the more traditional connection string format (mongodb://). Remove any SRV records temporarily to test if it resolves the connection issue. For example:

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3. Investigate DNS Configuration

If your ASP.NET application is incorrectly resolving the MongoDB IP, check your DNS settings to ensure they don’t conflict. Verify if your app is referencing a local DNS configuration which could lead to incorrect routing.

4. Upgrade MongoDB Drivers

Keep your MongoDB driver package versions updated to benefit from the latest patches and features. For instance:

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You can run a compatibility check for your ASP.NET Version and the MongoDB drivers.

Conclusion

Errors in connecting to MongoDB Atlas can be frustrating, but understanding the implications behind them can significantly ease troubleshooting. By dissecting the error message and inspecting your configuration, you can narrow down the problem effectively. As always, make sure to keep your environment updated and configured properly to avoid such issues in future development.

With these strategies, you should feel more confident in di