Скачать или смотреть How to Resolve the Issue of Your .NET Core API Not Responding in a Docker Container

Learn how to troubleshoot and fix the common issue of an ASP.NET Core API not responding when run in a Docker container using step-by-step guidance and solutions.
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This video is based on the question https://stackoverflow.com/q/69425200/ asked by the user 'GPGVM' ( https://stackoverflow.com/u/1278561/ ) and on the answer https://stackoverflow.com/a/69426208/ provided by the user 'Camilo Terevinto' ( https://stackoverflow.com/u/2141621/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Resolve the Issue of Your .NET Core API Not Responding in a Docker Container

If you're a developer transitioning to containerized applications, you may run into scenarios where your API, while functioning correctly in local development environments, fails to respond when packed into a Docker container. This is a common issue, particularly when working with ASP.NET Core applications. In this guide, we'll dive into a specific case where an ASP.NET Core API built with Visual Studio responds in its local environment but not in a Docker setting, and provide solutions to resolve it.

The Problem: API Not Responding in Docker

You have created a basic API in ASP.NET Core that works perfectly when run directly from Visual Studio (VS 2019). However, when you attempt to access it through Postman after deploying it within a Docker container through Docker Desktop, it doesn't respond to your requests, leaving you puzzled.

API Details

Your API is basic yet effective, returning "Alive" when accessed via a specific HTTP GET request. The immediate issue you faced was that even though the container was running, it did not respond when you sent a request to http://localhost:5150/HealthCheck/basic using Postman.

Understanding Docker Networking and Ports

When deploying your API to a Docker container, the way services communicate over networks changes. Here are the key points to understand:

Docker Binding: By default, ASP.NET Core services may listen on port 80, especially when not explicitly defined, which can lead to confusion when trying to access them externally.

Exposed Ports: When you declared ports: "5150:5150" in your Docker Compose file, you meant for the service to be accessible on port 5150; however, this only works correctly if the application inside the container is set to listen on this same port.

The Solution: Step-by-Step Guide

To resolve the issue of your API not responding in Docker, follow these steps:

1. Understanding Default Port Configuration

By examining your Docker inspect command output, you found that ASP.NET Core was defaulting to listen on port 80 via the environment variable:

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

This automatic port assignment can lead to confusion since your launchSettings.json suggests a different port for debugging in Visual Studio.

2. Updating the ENTRYPOINT Command

You need to explicitly tell your application to listen on the desired port (5150). Update the ENTRYPOINT in your Dockerfile as follows:

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

This command configures your ASP.NET Core application to handle requests on port 5150, matching your Docker port binding.

3. Rebuilding Your Docker Image

To ensure that your changes take effect, you will need to rebuild your Docker containers with the following commands:

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

Using the --no-cache option ensures that Docker rebuilds your images entirely, reflecting any changes you've made. --force-recreate makes sure the containers are recreated, enforcing your updates.

4. Testing with Postman

Once your container is running again, retest by sending a request to http://localhost:5150/HealthCheck/basic using Postman. You should receive the expected "Alive" response, indicating successful functionality.

Conclusion

Working with Docker can be tricky, especially when transitioning from a local development environment to containerized deployments. By following the steps outlined above, you can troubleshoot the issue of your ASP.NET Core API not responding when run in a Docker container. The keys are understanding Docker’s networking behavior, configuring your application to listen on the correct