How to Connect Two Docker Containers with MongoDB and Python

Learn how to connect two Docker containers, one running a MongoDB database and the other using Python with PyMongo. Follow our step-by-step solution to solve connection issues effectively.
---
This video is based on the question https://stackoverflow.com/q/71299758/ asked by the user 'Slava Bugz' ( https://stackoverflow.com/u/12039847/ ) and on the answer https://stackoverflow.com/a/71299985/ provided by the user 'Belly Buster' ( https://stackoverflow.com/u/10490683/ ) 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: Connecting two containers MongoDB + Python project

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.
---
Connecting Two Docker Containers with MongoDB and Python

Connecting two Docker containers can sometimes be challenging, especially when one container is running a MongoDB database, and another is using Python to interact with it. If you've encountered connection errors while trying to reach your MongoDB from your Python application, you're not alone! In this guide, we will explore how to successfully connect these two components within Docker, understand the common mistakes, and offer a clear solution.

The Problem

A user reached out with a specific issue: they were unable to connect from one Docker container (the Python application) to another (the MongoDB container). While the connection worked perfectly from the host machine, attempts to connect from one container to the other resulted in errors like:

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

This can be frustrating, but don't worry—this issue is easier to resolve than you might think!

Understanding the Setup

In their Docker setup, the user was utilizing a docker-compose.yaml file, which is standard practice for defining and running multi-container Docker applications. Here’s a concise breakdown of their setup:

Network: A shared bridge network was defined to enable communication between the containers.

Services: Two services were specified — one for the application (Python) and another for MongoDB.

Ports: MongoDB was set up to expose port 27017.

Here's a simplified version of the configuration:

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

The Solution

The key issue here is that while running inside Docker containers, you cannot use localhost to refer to the MongoDB service. Instead, you should use the name of the service as defined in the docker-compose.yaml file. This is how Docker networks containers effectively.

Step-by-Step Fix

Modify Connection String: In your Python application, change the connection string within your get_connection function. Replace localhost with the service name mongo.

Here's the modified code:

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

Rebuild and Restart Containers: After making the changes, you'll need to rebuild the Docker containers to ensure they use the updated code. This can be done with the following commands:

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

Test the Connection: Once the containers are up and running, test your connection from the Python application to see if the issue has been resolved.

Conclusion

By simply using the correct service name (mongo in this case) instead of localhost, you can successfully connect your Python application container to your MongoDB container. This approach is crucial when working within a multi-container environment like Docker.

If you're facing similar connection issues or have further questions, feel free to comment below. Happy coding!