Solving the Mysterious Case of "Connection Refused" Http Calls between .NET Controllers Running on Docker Containers

Are you tired of seeing the dreaded "Connection Refused" error when making HTTP calls between .NET controllers running on Docker containers? Do you feel like you’ve tried every solution under the sun, but the problem still persists? Fear not, dear developer, for we’re about to dive into the depths of this issue and emerge victorious with a comprehensive guide to solving this frustrating problem.

What’s Causing the "Connection Refused" Error?

Before we dive into the solutions, let’s take a step back and understand what’s causing this error in the first place. When you make an HTTP call from one .NET controller to another, the request is sent over the network, and the target controller needs to be reachable. If the target controller is not reachable, or if there’s an issue with the network configuration, the "Connection Refused" error is thrown.

Possible Causes:

• Firewall rules blocking the requests
• Incorrect container networking configuration
• Container ports not exposed correctly
• Controller not listening on the expected port
• DNS resolution issues

Step 1: Verify Container Networking Configuration

Let’s start by checking the container networking configuration. When you run your .NET controllers as Docker containers, you need to ensure that they’re connected to the same network. You can do this by creating a bridge network and attaching both containers to it.

docker network create my-network
docker run -d --name controller1 --network my-network -p 8080:80 controller1-image
docker run -d --name controller2 --network my-network -p 8081:80 controller2-image

In this example, we create a bridge network called "my-network" and attach both containers to it. This allows them to communicate with each other.

Step 2: Expose Container Ports Correctly

Now that we have our containers connected to the same network, let’s ensure that the container ports are exposed correctly. In your Dockerfile, you need to expose the port that your controller is listening on.

FROM mcr.microsoft.com/dotnet/core/sdk:3.1
WORKDIR /app
COPY . .
RUN dotnet restore
RUN dotnet publish -c Release
EXPOSE 80
CMD ["dotnet", "MyController.dll"]

In this example, we expose port 80, which is the default port that .NET controllers listen on.

Step 3: Verify Controller Configuration

Next, let’s verify that your controllers are configured to listen on the correct port. In your .NET controller code, make sure that you’re listening on the expected port.

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
    app.UseRouting();
    app.UseEndpoints(endpoints =>
    {
        endpoints.MapControllers();
    });
    app.Listen("http://0.0.0.0:80");
}

In this example, we’re listening on port 80, which is the default port.

Step 4: Verify DNS Resolution

Another common issue that can cause the "Connection Refused" error is DNS resolution. When you make an HTTP call to another controller, the DNS needs to resolve the hostname to the correct IP address.

To verify DNS resolution, you can use the following command:

docker exec -it controller1 ping controller2

This command will ping the other container using its hostname. If the DNS resolution is not working, you’ll see an error message.

Step 5: Check Firewall Rules

Finally, let’s check the firewall rules to ensure that they’re not blocking the requests. You can use the following command to check the firewall rules:

docker exec -it controller1 iptables -L

This command will list the current firewall rules. If you see any rules that are blocking the requests, you can use the following command to add a rule to allow incoming requests:

docker exec -it controller1 iptables -A INPUT -p tcp --dport 80 -j ACCEPT

In this example, we add a rule to allow incoming requests on port 80.

Conclusion

And there you have it, folks! By following these steps, you should be able to resolve the "Connection Refused" error when making HTTP calls between .NET controllers running on Docker containers. Remember to verify your container networking configuration, expose container ports correctly, verify controller configuration, verify DNS resolution, and check firewall rules.

By following these steps, you’ll be well on your way to creating a robust and scalable microservices architecture using .NET controllers and Docker containers.

Step	Description
1	Verify container networking configuration
2	Expose container ports correctly
3	Verify controller configuration
4	Verify DNS resolution
5	Check firewall rules

Remember, troubleshooting can be a tedious process, but by following these steps, you’ll be able to identify and resolve the issue quickly and efficiently.

Common Pitfalls to Avoid

Here are some common pitfalls to avoid when troubleshooting the "Connection Refused" error:

• Not exposing the correct port in the Dockerfile
• Not verifying DNS resolution
• Not checking firewall rules
• Not verifying controller configuration
• Not using the correct hostname or IP address when making the HTTP call

By avoiding these common pitfalls, you’ll be able to troubleshoot the issue quickly and efficiently.

Final Thoughts

In conclusion, resolving the "Connection Refused" error when making HTTP calls between .NET controllers running on Docker containers requires a thorough understanding of container networking, port exposure, controller configuration, DNS resolution, and firewall rules. By following the steps outlined in this article, you’ll be able to identify and resolve the issue quickly and efficiently.

Remember to stay calm, patient, and methodical when troubleshooting this issue. With practice and experience, you’ll become a master troubleshooter, and your .NET controllers will be communicating with each other in no time!

Happy troubleshooting, and see you in the next article!

Here are 5 Questions and Answers about “Connection Refused” HTTP calls between .NET controllers running on Docker containers:

Frequently Asked Question

Stuck with “Connection Refused” errors between your .NET controllers running on Docker containers? Fear not, we’ve got you covered!