Скачать или смотреть Solving the Docker Postgres Connection Issues on Non-Standard Ports

Learn how to troubleshoot Docker Postgres connection problems when using non-standard ports. Understand the differences between internal and external connections in Docker setup.
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Solving the Docker Postgres Connection Issues on Non-Standard Ports

Running a Postgres database within a Docker container can simplify many aspects of application deployment. However, you might encounter some issues when trying to connect to Postgres on non-standard ports. In this guide, we’ll explore the question:

Why can I connect to Postgres on port 5432 from other containers but not on port 5433?

Understanding Ports in Docker

Before diving into the solution, it’s essential to understand how Docker handles networking, especially when it comes to ports.

Two Types of Ports in Docker

Exposed Ports: These are intended for internal container communication.

Mapped Ports: These are used for external access from the host machine to the container.

When you define ports in your Docker Compose file, you might see something like this:

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

Here’s what this means:

The first port number (before the colon) is the port on your host machine.

The second number (after the colon) is the port inside the Docker container.

Why Can't You Connect on Port 5433?

The problem arises from a common misconception about how Docker manages connections between containers. When other containers try to connect to the Postgres database, they do not use the mapped (host) port, but rather the internal port of the service.

Key Points to Remember:

Internal Connections: Other containers only need to reference the service's running port, which is 5432 in your case. Thus, even if you've mapped it to 5433 on the host, internal connections ignore this mapping.

No Need for Ports in Internal Networking: As containers operate with their unique private IP addresses, there’s no need for port remapping for internal communication.

Solution to the Problem

If you are trying to connect between containers in your Docker setup, always use the internal port number:

Steps to Follow:

Use Port 5432 for Internal Connections: Adjust your connection in any other container to point to port 5432 since it is the internal port that the Postgres service listens to.

Accessing from Outside: If you want to connect to your Postgres database from outside of Docker (e.g., from your local machine), you can use port 5433 directly, which will be forwarded to the Postgres service running inside the container on port 5432.

Example Connection String

When connecting from another Docker container, use:

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

Here, proj-database is your container name, your_username is your Postgres username, and your_database is the name of your database.

Conclusion

Understanding the concept of port mapping in Docker is crucial for effective communication between containers and external access. When working with Docker containers, remember to always use the internal port for connections between containers. By following these guidelines, you can resolve connection issues effectively and streamline your development process with Docker and Postgres.

For any inquiries or further assistance, feel free to leave a comment below!