Скачать или смотреть Troubleshooting Docker Compose Service Connection Issues: Resolving ECONNREFUSED Errors

Discover how to troubleshoot connection issues between Docker Compose services, specifically resolving the `ECONNREFUSED` error when making API calls.
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Understanding ECONNREFUSED Errors in Docker Compose

When working with Docker Compose, you may encounter various issues, one of which is the dreaded ECONNREFUSED error. This problem often arises when one service tries to connect to another that is not running or is unreachable. In this guide, we will explore a specific scenario involving a web server that attempts to communicate with an API server, leading to connection difficulties.

The Problem

In our example, we have a development environment set up using Docker Compose, which runs multiple services. Below is a simplified version of the docker-compose.yml file:

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In this configuration:

The webserver handles a BullMQ queue and communicates with a Redis service.

The apiserver is expected to respond to HTTP requests on port 8383.

However, a connection error arises when the webserver tries to request an endpoint on the apiserver using the URL http://apiserver:8383/endpoint. The error generated is:

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This indicates that the attempt to connect to the apiserver failed because it couldn't establish a connection.

Solution: Diagnose and Resolve the Issue

Step 1: Verify Service Status

The first step in troubleshooting is to check whether the apiserver is actually running and accepting connections. You can do this by following these steps:

Access the Redis container: Use SSH to enter the Redis container.

Attempt to connect to the API server:

Use a command like wget to test connectivity:

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If you receive a message indicating "Connection refused", it suggests that the apiserver is not running.

Step 2: Check Docker Startup Messages

In this case, it turns out that the underlying issue was related to the server's resource allocation. The apiserver was killed by Docker because it was consuming too much memory. Therefore, no connections could be established because the server was not operational.

To view the startup messages for your services, use the command:

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Look for any error messages or indications that the apiserver has been stopped or killed.

Step 3: Adjust Resource Allocation

If you find that the apiserver is being killed due to resource constraints:

Consider increasing memory limits in your Docker configuration:

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Step 4: Restart Services

After making any necessary adjustments, ensure all services are restarted so the new configurations take effect:

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Conclusion

Connection issues between services in Docker Compose are common and can often be traced back to one service not running or being unreachable. In this scenario, we learned that the ECONNREFUSED error stemmed from the apiserver being killed due to memory usage. By checking logs and ensuring adequate resources are allocated, we can resolve these errors effectively.

If you ever find yourself facing similar issues, remember to check your service's status, examine startup logs, and adjust resource allocations as needed. Happy coding!