dotnetcore console app : rabbitmq with docker Connection refused 127.0.0.1:5672

2 min read 06-10-2024

dotnetcore console app : rabbitmq with docker Connection refused 127.0.0.1:5672

"Connection Refused" - Troubleshooting RabbitMQ with Docker in .NET Core Console Applications

The Problem:

You're building a .NET Core console application that uses RabbitMQ for message queuing, running everything within Docker containers. You've configured everything correctly, but when you try to connect to your RabbitMQ container, you're met with the dreaded "Connection Refused" error on port 5672.

The Scenario:

Let's imagine you have a simple .NET Core console application (like the one below) that sends a message to a RabbitMQ queue. The application and RabbitMQ are both running in separate Docker containers:

using RabbitMQ.Client;

public class Program
{
    public static void Main(string[] args)
    {
        var factory = new ConnectionFactory() { HostName = "rabbitmq" };
        using var connection = factory.CreateConnection();
        using var channel = connection.CreateModel();

        channel.QueueDeclare(queue: "hello",
                             durable: false,
                             exclusive: false,
                             autoDelete: false,
                             arguments: null);

        string message = "Hello from .NET Core!";
        channel.BasicPublish(exchange: "",
                             routingKey: "hello",
                             basicProperties: null,
                             body: Encoding.UTF8.GetBytes(message));

        Console.WriteLine(" [x] Sent {0}", message);
        Console.ReadLine();
    }
}

Your Dockerfile for the RabbitMQ container might look like this:

FROM rabbitmq:3-management

EXPOSE 5672 15672

You run both containers and you can see the RabbitMQ management interface running on port 15672, but your application throws the error: System.Net.Sockets.SocketException: No connection could be made because the target machine actively refused it 127.0.0.1:5672.

Understanding the Issue:

The root of the problem is often a network configuration issue within Docker. Here's why:

Docker Networking: By default, Docker containers are isolated from each other and from the host machine's network. This means that your .NET Core application can't directly reach the RabbitMQ container on its default port (5672).
Container Communication: To enable communication between containers, you need to use a Docker network. Docker networks allow containers to communicate with each other by creating a virtual network within the Docker environment.

The Solution:

Define a Docker Network: Create a shared network that both containers will join. This ensures they can talk to each other.

version: '3.7'

services:
  rabbitmq:
    image: rabbitmq:3-management
    ports:
      - "15672:15672"
    networks:
      - my-network 
  dotnetcore-app:
    build: .
    networks:
      - my-network
networks:
  my-network:
    driver: bridge

Connect Containers to the Network: In your docker-compose.yml file, link both your RabbitMQ and application containers to the my-network network you created.
Update Hostname: Modify your .NET Core application code to connect to the RabbitMQ container using its hostname within the network. Instead of HostName = "rabbitmq" use HostName = "rabbitmq" (the service name defined in docker-compose.yml)

Additional Insights:

Other Docker Networking Options: Docker provides various networking options beyond the simple bridge network, like overlay and macvlan, each with specific use cases.
Docker Compose for Orchestration: Docker Compose simplifies running multi-container applications. It lets you define your application's services, networks, and volumes in a single file, making it easier to manage and deploy.
Debugging Tools: When faced with networking errors, use tools like docker network inspect, docker logs, and docker exec to inspect the network configuration and container logs for clues about the problem.

Conclusion:

"Connection Refused" errors in Dockerized .NET Core applications using RabbitMQ are often caused by improper network configuration. By understanding Docker's network isolation and utilizing shared networks, you can ensure seamless communication between your application and RabbitMQ containers. Remember to use tools like Docker Compose and Docker network commands for easy configuration and troubleshooting.