Скачать или смотреть Resolving nginx Docker Compose Error: Host Not Found in Upstream "app"

Discover how to fix the `nginx` "host not found" error in Docker Compose setups with our comprehensive guide.
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Troubleshooting Nginx Docker Compose Error: Host Not Found in Upstream "app"

When working with Docker Compose, developers can occasionally encounter issues that can be confusing and time-consuming to resolve. One such problem is the error message:

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This error typically arises when setting up Nginx as a reverse proxy for a web application container, often indicating that the Nginx server is unable to locate the specified upstream application. In this guide, we will explore what causes this error and how you can efficiently solve it.

Understanding Your Setup

In your setup, you have:

A web application running on Node.js.

An Nginx server configured to reverse proxy requests to the application.

Here's a brief outline of your configuration files:

Dockerfile

The Dockerfile is used for building your Node.js application. It performs several steps, such as installing dependencies and building the application.

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Nginx Configuration (default.conf)

This is the Nginx configuration that sets up the server to listen on multiple ports and handle SSL:

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Docker Compose File

Your docker-compose.yml defines the services and how they interact:

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Fixing the Error

Now, let’s tackle the error you’re encountering.

1. Update the proxy_pass Directive

In your Nginx configuration (default.conf), you need to modify the proxy_pass directive from https://app:3000 to http://app:3000. This change is crucial because SSL termination happens at Nginx itself, and your application is still using HTTP:

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2. Modify the Docker Compose Configuration

Since the links parameter is deprecated in Docker Compose, it's preferable to use depends_on to ensure that Nginx starts after the application service. Here’s the updated docker-compose.yml file:

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Conclusion

By following the outlined changes to both your Nginx configuration and Docker Compose setup, you should be able to resolve the issue of the “host not found” error. Always ensure that the protocol used in the proxy_pass statement aligns with how your services communicate.

If you encounter further issues, double-check your service names and ensure that all configurations are saved before restarting your Docker containers with docker-compose up.

With this knowledge, you’ll be more equipped to handle similar issues in the future and maintain a smooth-running environment with Docker and Nginx.