Self-Hosting PostgreSQL on RHEL with Docker and Nginx Reverse Proxy

Learn how to set up PostgreSQL in a Docker container on a RHEL VM, configure Nginx as a reverse proxy, and make your database accessible from another machine securely. This guide covers each step from creating a Docker Compose setup for PostgreSQL to configuring firewalls and security settings.

Prerequisites

• Docker installed on the RHEL VM.
  You can follow the official Docker documentation for installation on RHEL:
  👉 Install Docker Engine on RHEL

Steps

1. Create a Directory Structure

   Organize your PostgreSQL setup by creating a services directory and a subdirectory for PostgreSQL.

   mkdir -p services/postgres
   cd services/postgres

2. Create the docker-compose.yml File

   This file defines the Docker services for PostgreSQL.

   touch docker-compose.yml
   vi docker-compose.yml

   Add the following configuration to the docker-compose.yml file:

   version: '3.9'
   
   services:
     postgres:
       image: postgres:latest
       container_name: postgresql
       environment:
         POSTGRES_USER: postgres
         POSTGRES_PASSWORD: postgres
         POSTGRES_DB: testdb
       ports:
         - "5432:5432"
       volumes:
         - pgdata:/var/lib/postgresql/data
       mem_limit: 3g      # Limit memory usage to 3 GB
       cpus: 1.5          # Limit to 1.5 CPUs
   
   volumes:
     pgdata:

   • This configuration pulls the latest PostgreSQL image and sets environment variables for the user, password, and database name.
   • The ports section maps port 5432 on the host to port 5432 in the container, allowing external connections.
   • The pgdata volume ensures data persists even if the container is removed.

3. Configure the Firewall

   Allow traffic through the firewall for the PostgreSQL and Nginx proxy ports.

   sudo firewall-cmd --add-port=5432/tcp --permanent
   sudo firewall-cmd --add-port=9856/tcp --permanent

4. Enable Network Connections for Nginx (TCP Streams)

   Since we’re using Nginx’s TCP stream module, we need to adjust SELinux settings to allow such connections. Run the following command:

   sudo setsebool -P nis_enabled 1

   This enables the nis_enabled boolean, which allows services like Nginx to establish outbound TCP connections — necessary for proxying PostgreSQL connections.

5. Reload the Firewall

   Reload the firewall to apply these changes.

   sudo firewall-cmd --reload

6. Start PostgreSQL with Docker Compose

   Bring up the PostgreSQL container in detached mode using the Docker Compose plugin (note the space between docker and compose):

   sudo docker compose up -d

   This command uses the Docker Compose plugin (recommended for modern Docker installations) to start the PostgreSQL container in the background.

7. Access PostgreSQL

   Confirm that PostgreSQL is running by accessing it from within the container:

   sudo docker exec -it postgresql psql -U postgres -d testdb

   This command opens an interactive psql session connected to the testdb database as the postgres user.

8. Install Nginx

   Install Nginx if it is not already installed.

   sudo yum install nginx

9. Configure Nginx as a TCP Proxy

   Nginx can act as a reverse proxy, forwarding requests on port 9856 to PostgreSQL’s port 5432.

   • Create a configuration file for the proxy setup using sudo to ensure proper permissions:

     sudo touch /usr/share/nginx/modules/postgres.conf
     sudo vi /usr/share/nginx/modules/postgres.conf

   • Add the following configuration:

     stream {
         server {
             listen 9856;
             proxy_connect_timeout 60s;
             proxy_pass localhost:5432;
         }
     }

10. Restart Nginx

    Apply the new configuration by restarting Nginx:

    sudo systemctl restart nginx

11. Test the Connection

    Verify that Nginx is successfully forwarding requests by using nc (netcat) from another machine or your VM:

    nc -vz <your_private_ip> 9856

    Replace <your_private_ip> with the actual private IP address of your RHEL VM. This command will check if the connection to the PostgreSQL service is being forwarded correctly through Nginx.

12. Open Port 9856 in VM's Security Settings

    Make sure that your VM's network security settings (e.g., security groups, ingress rules) allow access to port 9856.

13. Connect from Another Machine

    From a different VM or machine, connect to PostgreSQL using the Nginx proxy:

    psql -h <your_host> -p 9856 -U postgres -d testdb

    Replace <your_host> with the IP address of your VM. This command should establish a remote connection to the PostgreSQL instance hosted in Docker.

Summary

With these steps, you have successfully set up a PostgreSQL database in a Docker container on RHEL, configured Nginx as a reverse proxy to forward external traffic, and opened necessary ports. This setup ensures that your database is accessible securely and can handle incoming connections from other machines on the network.