Скачать или смотреть How to Fix PostgreSQL Connection Errors in Docker Containers

Learn how to resolve connection errors when using PostgreSQL with Python in Docker containers. This guide offers step-by-step instructions to fix your setup.
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This video is based on the question https://stackoverflow.com/q/69662587/ asked by the user 'civy' ( https://stackoverflow.com/u/5726268/ ) and on the answer https://stackoverflow.com/a/69662728/ provided by the user 'Máté Tősér' ( https://stackoverflow.com/u/13184919/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Troubleshooting PostgreSQL Connection Errors in Docker Containers

Setting up a development environment using Docker can be incredibly powerful and flexible. However, it is not uncommon to experience issues when trying to connect to a database from another container. In this post, we will explore a common problem: connecting to a PostgreSQL database from a Python container using Docker, along with the required solution.

The Problem: Connection Refused Error

Imagine this situation: you have two Docker containers set up to work together:

Container 1: PostgreSQL instance to hold data

Container 2: A Python-based Jupyter notebook for querying the database

You've configured everything correctly, built your Docker containers, and are trying to establish a connection from your Python container to your PostgreSQL database. However, upon executing your connection code, you receive the following error message:

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

This error message indicates that the Python container is unable to connect to the PostgreSQL instance running in another container. But why is that?

Understanding the Cause

In your Docker setup, you are trying to connect to PostgreSQL using the hostname 0.0.0.0. However, this IP address is not appropriate for inter-container communication. The key takeaway here is that 0.0.0.0 refers to all addresses on the local machine, and it does not correctly route the request to the PostgreSQL container.

Instead, you should use the service name defined in your docker-compose.yml file. In your case, this name is db. Docker Compose automatically sets up a network between the services, allowing them to communicate using their service names as hostnames.

The Solution: Correcting the Hostname

To solve this connection problem, you will need to modify your connection string in your Python code. Change the hostname from 0.0.0.0 to the service name db:

Updated Connection Code

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

Wrapping Up

Now, when you run your updated connection code, it should successfully establish a connection to the PostgreSQL database. Here’s a recap of what you learned:

Use the service name defined in your Docker Compose file to connect between containers.

0.0.0.0 is not suitable for inter-container communication; use the service name instead.

By following these steps, you should be able to troubleshoot and resolve the connection issues between your PostgreSQL and Python containers in Docker effectively. Happy coding!