Скачать или смотреть Troubleshooting Docker-Compose: Can't Connect to Docker PostgreSQL Container? Here’s the Fix!

Struggling to connect your Docker-Compose application with a PostgreSQL database? Discover why it happens and how to solve the 'Unknown host exception' issue effectively in this comprehensive guide.
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Troubleshooting Docker-Compose: Can't Connect to Docker PostgreSQL Container? Here’s the Fix!

When working with Docker and Docker-Compose, it's not uncommon to run into connectivity issues between your application container and your PostgreSQL database container. One of the most frequently encountered problems is the application's inability to connect to the PostgreSQL database, even though everything seems to be configured correctly. If you're facing this issue, you're certainly not alone! In this guide, we'll dissect the problem and provide you with a practical solution.

The Problem: Can't Connect to PostgreSQL Container

In your setup, you have two containers: one for the PostgreSQL database and another for your application using Spring Boot. Your PostgreSQL container is configured to use port 5432, and you've set your application to depend on it. However, when you try to connect to the database with a JDBC URL, you receive an "Unknown host exception" error.

Configuration Overview

Here's a brief overview of your configurations:

PostgreSQL Container:

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

Application Container:

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

The JDBC Connection URL

You updated your connection settings in the Spring Boot application as follows:

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

However, even after making this change, your application still tries to connect to localhost:5432. This leads to confusion and results in connection errors.

The Solution: Switch to Host Network Mode

The issue here is likely related to how Docker manages networking between containers. When using bridge mode, each container is isolated, and communication occurs over names or IPs. However, changing the network_mode to host allows the containers to share the host's network stack, which can resolve communication issues.

Steps to Fix The Issue:

Update the Network Mode for Both Containers:
Change the network_mode from bridge to host in your PostgreSQL and application configurations as follows:

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

Remove the Expose Option:
Note that when using the host network mode, the expose option is ignored and won't be necessary.

Restart Your Containers:
After making these changes, don’t forget to restart your Docker containers to apply the new configurations.

Advantages of Using Host Network Mode

Simplicity: Since both containers share the network stack, they can communicate seamlessly without needing to rely on Docker networking.

Performance: There is often improved performance because there is no overhead of network isolation.

Conclusion

By changing the network_mode to host, you alleviate many of the connectivity issues you might face when using Docker-Compose with PostgreSQL. This method simplifies communication between your application and database.

If you're still facing challenges or have any questions regarding Docker and container management, feel free to reach out. Happy coding!