Скачать или смотреть Troubleshooting FastAPI Connection Issues in Docker: Failed to connect to localhost port 8383

Are you facing connection issues with your FastAPI server running in a Docker container? This guide provides a step-by-step solution to resolve the `Failed to connect to localhost port 8383` error.
---
This video is based on the question https://stackoverflow.com/q/74917684/ asked by the user 'e-e' ( https://stackoverflow.com/u/2543424/ ) and on the answer https://stackoverflow.com/a/74917700/ provided by the user 'e-e' ( https://stackoverflow.com/u/2543424/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: FastAPI server running inside Docker container: Failed to connect to localhost port 8383 after 0 ms: Connection refused

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Troubleshooting FastAPI Connection Issues in Docker

Running a FastAPI server in a Docker container can sometimes lead to frustrating connection issues, especially when deployed on cloud infrastructure like AWS EC2. If you've encountered the error message Failed to connect to localhost port 8383 after 0 ms: Connection refused, you're not alone—this is a common issue that can usually be resolved with the right configuration. Here’s a clear and organized guide to help you troubleshoot and fix this problem.

Understanding the Problem

Server Setup: You have an EC2 instance with a containerized FastAPI server that successfully starts and indicates it's listening on 0.0.0.0:8383.

Successful Access from Within: You can SSH into the instance and access the FastAPI root endpoint using curl http://localhost:8383.

Failed Access from Host: When trying to curl the same endpoint from the host machine, you receive a connection error, indicating that the port is not openly accessible.

Possible Causes

This behavior suggests that while the server is running inside the Docker container, the port used by the FastAPI application is not published correctly to the host.

Solution Steps

1. Understanding Docker Port Binding

The main reason for the Connection refused error is that merely using the --expose flag in your docker run command does not make ports available to the host machine. The --expose flag merely documents the port but does not publish it.

Correct Command

To correctly bind the port so it can be accessed externally from your host machine, use the -p option instead of --expose. Your run command should look like this:

[[See Video to Reveal this Text or Code Snippet]]

In this command:

-p 8383:8383: The first 8383 refers to the host port, and the second 8383 refers to the container port. This setup allows incoming traffic on port 8383 from the host to be forwarded to port 8383 in your Docker container.

2. Check Your Dockerfile Configuration

Ensure your Dockerfile is configured correctly for the FastAPI server to listen on the intended port. Here’s a simplified example based on your provided Dockerfile:

[[See Video to Reveal this Text or Code Snippet]]

This configuration allows your FastAPI server to listen on the specified port within the container.

3. Verify Nginx Configuration

For those using Nginx as a reverse proxy, ensure that your Nginx configuration routes requests correctly to the FastAPI application. Your configuration should contain:

[[See Video to Reveal this Text or Code Snippet]]

4. Restart Docker

After making changes to your Docker run command or Nginx configuration, it may be beneficial to stop and restart your Docker containers. This guarantees that all changes take effect.

Command to Restart

Simply run:

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

By following these steps, you should be able to successfully resolve the Failed to connect to localhost port 8383 error when running a FastAPI server inside a Docker container.

Remember that using the -p option to publish your ports is crucial for making your services accessible outside the container. With proper configuration of both Docker and Nginx, you will ensure a smooth deployment of your FastAPI application on your EC2 instance.



For further assistance, don’t hesitate to reach out or check the FastAPI and Docker documentation for more advanced configurations. Happy coding!