How to Connect

Connecting with Node.js
Connecting with Python
Connecting with PHP
Connecting with Go
Connecting with Java
Connecting with psql
Connecting with pgAdmin

Connecting with Node.js

This guide walks you through the process of connecting a Node.js application to a Hydra database using the pg package. You’ll learn how to set up the environment, configure the connection, and run a simple SQL query.

Variables

To connect to a Hydra database, the following parameters are required. You can find these details in the Elestio service overview page of your Hydra service.

Variable	Description	Purpose
`USER`	Hydra (PostgreSQL) username	Identifies the database user with access privileges
`PASSWORD`	Hydra password	Authenticates the user against the Hydra database
`HOST`	Hostname of the Hydra instance	Specifies the server address of the database
`PORT`	Port for Hydra (usually 5432)	Specifies the network port for connections
`DATABASE`	Name of the Hydra database	Specifies which database to access

These values can usually be found in the Elestio service overview details as shown in the image below, make sure to take a copy of these details and add it to the code moving ahead.

Prerequisites

Install Node.js and NPM
- Check if Node.js is installed:

node -v
npm -v

- If not, download and install it from https://nodejs.org.
Install the pg Package
- Hydra is PostgreSQL-compatible, so use the pg package:

npm install pg --save

Code

Once all prerequisites are set up, create a new file named hydra.js and add the following code.

const { Client } = require("pg");

// Database connection configuration
const config = {
  host: "HOST",
  user: "USER",
  password: "PASSWORD",
  database: "DATABASE",
  port: PORT,
  ssl: {
    rejectUnauthorized: false, // Only if Hydra requires SSL (check Elestio settings)
  },
};

// Create a new client instance
const client = new Client(config);

// Connect to the Hydra database
client.connect((err) => {
  if (err) {
    console.error("Connection failed:", err.stack);
    return;
  }

  console.log("Connected to Hydra");

  // Run a test query
  client.query("SELECT version()", (err, res) => {
    if (err) {
      console.error("Query failed:", err.stack);
    } else {
      console.log("Hydra/PostgreSQL Version:", res.rows[0].version);
    }

    // Close the connection
    client.end((err) => {
      if (err) console.error("Error closing connection:", err.stack);
    });
  });
});

To execute the script, open the terminal or command prompt and navigate to the directory where hydra.js. Once in the correct directory, run the script with the command

node hydra.js

If successful, you’ll see:

Connected to Hydra
Hydra/PostgreSQL Version: PostgreSQL 14.13 (Debian 14.13-1.pgdg120+1) on x86_64-pc-linux-gnu, compiled by gcc (Debian 12.2.0-14) 12.2.0, 64-bit

Connecting with Python

This guide explains how to connect a Python application to a Hydra database using the psycopg2-binary package. It covers environment setup, configuration, and execution of a simple query to test connectivity.

Variables

To connect to a Hydra database, you only need one environment variable — the connection URI.

Variable	Description	Purpose
`HYDRA_URI`	Full Hydra (PostgreSQL-compatible) connection string from the Elestio service overview	Provides all credentials and connection details in a single URI

A typical URI format looks like:

postgresql://<USER>:<PASSWORD>@<HOST>:<PORT>/<DATABASE>

You can find the details needed in the URI from the Elestio service overview details. Copy and replace the variables carefully in the URI example provided above.

Prerequisites

Install Python

Check if Python is installed:

python --version

If not installed, download it from https://python.org.

Install psycopg2-binary

Install the PostgreSQL driver for Python:

pip install psycopg2-binary

Code

Once all prerequisites are set up, create a new file named hydra.py and add the following code and replace the HYDRA_URI with actual link or in environment setup as you wish:

import psycopg2
import os

def get_db_version():
    try:
        # Use the Hydra URI from environment variable
        connection_uri = os.getenv('HYDRA_URI', 'POSTGRESQL_URI')
        db_connection = psycopg2.connect(connection_uri)
        db_cursor = db_connection.cursor()
        db_cursor.execute('SELECT VERSION()')
        db_version = db_cursor.fetchone()[0]
        return db_version

    except Exception as e:
        print(f"Database connection error: {e}")
        return None

    finally:
        if 'db_cursor' in locals():
            db_cursor.close()
        if 'db_connection' in locals():
            db_connection.close()

def display_version():
    version = get_db_version()
    if version:
        print(f"Connected to Hydra: {version}")

if __name__ == "__main__":
    display_version()

🔐 Tip: Save your URI in an .env file or set it in your terminal session like this:

export HYDRA_URI=postgresql://user:password@host:port/database

To execute the script, open the terminal or command prompt and navigate to the directory where hydra.py. Once in the correct directory, run the script with the command

python hydra.py

If the connection is successful, you’ll see:

Connected to Hydra: PostgreSQL 14.13 (Debian 14.13-1.pgdg120+1) on x86_64-pc-linux-gnu, compiled by gcc (Debian 12.2.0-14) 12.2.0, 64-bit

Connecting with PHP

This guide explains how to connect a PHP application to a Hydra database using the PDO extension. It covers setting up prerequisites, configuring the connection URI, and running a test SQL query.

Variables

To connect to a Hydra database, you only need one environment variable — the connection URI.

Variable	Description	Purpose
`HYDRA_URI`	Full Hydra connection string from Elestio	Encodes all connection info in one URI

A typical URI looks like this:

postgresql://<USER>:<PASSWORD>@<HOST>:<PORT>/<DATABASE>

You can find the details needed in the URI from the Elestio service overview details. Copy and replace the variables carefully in the URI example provided above.

Prerequisites

Install PHP

Check if PHP is installed:

php -v

If not, download and install PHP from: https://www.php.net/downloads.php

Code

Once all prerequisites are set up, create a new file named hydra.php and add the following code and replace the HYDRA_URI with actual link or in environment setup as you wish:

<?php
$db_url = getenv("HYDRA_URI") ?: "postgresql://user:password@host:port/database";
$db_parts = parse_url($db_url);
$db_name = ltrim($db_parts['path'], '/');
$dsn = "pgsql:host={$db_parts['host']};port={$db_parts['port']};dbname={$db_name}";

try {
    $pdo = new PDO($dsn, $db_parts['user'], $db_parts['pass']);
    $version = $pdo->query("SELECT VERSION()")->fetchColumn();
    echo "Connected to Hydra: " . $version . PHP_EOL;
} catch (PDOException $e) {
    echo "Connection failed: " . $e->getMessage() . PHP_EOL;
}

To execute the script, open the terminal or command prompt and navigate to the directory where hydra.php. Once in the correct directory, run the script with the command

export HYDRA_URI=postgresql://user:password@host:port/database

Navigate to the directory containing hydra.php and run:

php hydra.php

If successful, you’ll see output like:

Connected to Hydra: PostgreSQL 14.13 (Debian 14.13-1.pgdg120+1) on x86_64-pc-linux-gnu, compiled by gcc (Debian 12.2.0-14) 12.2.0, 64-bit

Connecting with Go

This guide walks you through setting up a Go application to connect to a Hydra database, using the PostgreSQL-compatible lib/pq driver, and running a basic query to verify the connection.

Variables

To connect to a Hydra database, you only need one environment variable — the connection URI. This URI contains all the necessary information like username, password, host, port, and database name.

Variable	Description	Purpose
`HYDRA_URI`	Full Hydra (PostgreSQL-compatible) connection string from the Elestio service overview	Provides all credentials and connection details in a single URI

A typical URI format looks like:

postgresql://<USER>:<PASSWORD>@<HOST>:<PORT>/<DATABASE>

You can find the details needed in the URI from the Elestio service overview details. Copy and replace the variables carefully in the URI example provided above.

Prerequisites

Install Go
- Check if Go is installed:

go version

- If not, download and install Go: https://go.dev/dl/
Install pq Driver

go get github.com/lib/pq

Code

Once all prerequisites are set up, create a new file named main.go and add the following code, and replace the HYDRA_URI with actual link or in environment setup as you wish:

package main

import (
	"database/sql"
	"fmt"
	"log"
	"os"

	_ "github.com/lib/pq"
)

func getDBConnection(connStr string) (*sql.DB, error) {
	db, err := sql.Open("postgres", connStr)
	if err != nil {
		return nil, fmt.Errorf("failed to open database connection: %v", err)
	}

	if err := db.Ping(); err != nil {
		return nil, fmt.Errorf("failed to ping database: %v", err)
	}

	return db, nil
}

func main() {
	// Get the Hydra connection string from environment variable
	connStr := os.Getenv("HYDRA_URI")
	if connStr == "" {
		log.Fatal("HYDRA_URI environment variable not set")
	}

	db, err := getDBConnection(connStr)
	if err != nil {
		log.Fatal(err)
	}
	defer db.Close()

	query := "SELECT current_database(), current_user, version()"
	row := db.QueryRow(query)

	var dbName, user, version string
	if err := row.Scan(&dbName, &user, &version); err != nil {
		log.Fatal("Failed to scan row:", err)
	}

	fmt.Printf("Connected to Hydra\nDatabase: %s\nUser: %s\nVersion: %s\n", dbName, user, version)
}

Set your Hydra URI as an environment variable:

export HYDRA_URI=postgresql://user:password@host:port/database

To execute the script, open the terminal or command prompt and navigate to the directory where main.go. Once in the correct directory, run the script with the command

go run main.go

If successful, you’ll see output like:

Connected to Hydra
Database: elestio
User: postgres
Version: PostgreSQL 14.13 (Debian 14.13-1.pgdg120+1) on x86_64-pc-linux-gnu, compiled by gcc (Debian 12.2.0-14) 12.2.0, 64-bit

Connecting with Java

This guide shows how to connect your Java app to a Hydra database using the PostgreSQL JDBC driver, parse command-line arguments, and run a basic query.

Variables

To connect to a Hydra database, the following parameters are required. You can find these details in the Elestio service overview page of your Hydra service.

Variable	Description	Purpose
`USER`	Hydra (PostgreSQL) username	Identifies the database user with access privileges
`PASSWORD`	Hydra password	Authenticates the user against the Hydra database
`HOST`	Hostname of the Hydra instance	Specifies the server address of the database
`PORT`	Port for Hydra (usually 5432)	Specifies the network port for connections
`DATABASE`	Name of the Hydra database	Specifies which database to access

These values can usually be found in the Elestio service overview details as shown in the image below, make sure to take a copy of these details and add it to the code moving ahead.

Prerequisites

Install Java & JDBC driver

Check if Java is installed by running:

java -version

If not installed, install it first and then download and install JDBC driver from https://jdbc.postgresql.org/download/ or if you have Maven installed, run the following command with updated version of the driver:

mvn org.apache.maven.plugins:maven-dependency-plugin:2.8:get \  
  -Dartifact=org.postgresql:postgresql:42.7.5:jar \
  -Ddest=postgresql-42.7.5.jar

Code

Once all prerequisites are set up, create a new file named HydraPg.java and add the following code:

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.HashMap;
import java.util.Map;

public class HydraPg {

    static class Config {
        String host, port, database, username, password;

        Config(String host, String port, String database, String username, String password) {
            this.host = host;
            this.port = port;
            this.database = database;
            this.username = username;
            this.password = password;
        }

        String getJdbcUrl() {
            return String.format("jdbc:postgresql://%s:%s/%s?sslmode=require", host, port, database);
        }

        boolean isComplete() {
            return host != null && port != null && database != null && username != null && password != null;
        }
    }

    static Map<String, String> parseArgs(String[] args) {
        Map<String, String> map = new HashMap<>();
        for (int i = 0; i < args.length - 1; i += 2) {
            map.put(args[i], args[i + 1]);
        }
        return map;
    }

    public static void main(String[] args) {
        try {
            Class.forName("org.postgresql.Driver");

            Map<String, String> argMap = parseArgs(args);
            Config cfg = new Config(
                argMap.get("-host"),
                argMap.get("-port"),
                argMap.get("-database"),
                argMap.get("-username"),
                argMap.get("-password")
            );

            if (!cfg.isComplete()) {
                System.err.println("Missing required arguments. Example usage:");
                System.err.println("java -cp postgresql-42.7.5.jar:. HydraPg -host <HOST> -port <PORT> -database <DB> -username <USER> -password <PASS>");
                return;
            }

            try (Connection conn = DriverManager.getConnection(cfg.getJdbcUrl(), cfg.username, cfg.password)) {
                System.out.println("Connected to Hydra database successfully.");

                Statement stmt = conn.createStatement();
                ResultSet rs = stmt.executeQuery("SELECT current_database(), current_user, version()");

                while (rs.next()) {
                    System.out.println("Database: " + rs.getString(1));
                    System.out.println("User: " + rs.getString(2));
                    System.out.println("Version: " + rs.getString(3));
                }

                rs.close();
                stmt.close();
            }

        } catch (ClassNotFoundException e) {
            System.err.println("PostgreSQL JDBC driver not found.");
            e.printStackTrace();
        } catch (SQLException e) {
            System.err.println("Connection or query error:");
            e.printStackTrace();
        }
    }
}

To execute the script, open the terminal or command prompt and navigate to the directory where HydraPg.java. Once in the correct directory, run the script with the command (Update the variables with actual values acquired from previous steps).

javac HydraPg.java

java -cp postgresql-42.7.5.jar:. HydraPg -host HOST -port PORT -database DATABASE -username USERNAME -password PASSWORD

If the connection is successful, the terminal will display output similar to:

Connected to Hydra database successfully.
Database: elestio
User: postgres
Version: PostgreSQL 14.13 (Debian 14.13-1.pgdg120+1) on x86_64-pc-linux-gnu, compiled by gcc (Debian 12.2.0-14) 12.2.0, 64-bit

Connecting with psql

This guide explains how to connect to a Hydra database using the psql command-line tool. It walks through the necessary setup, connection process, and execution of a simple SQL query.

Variables

To connect to a Hydra database, you only need one environment variable — the connection URI.

Variable	Description	Purpose
`HYDRA_URI`	Full Hydra connection string from Elestio	Encodes all connection info in one URI

A typical URI looks like this:

postgresql://<USER>:<PASSWORD>@<HOST>:<PORT>/<DATABASE>

You can find the details needed in the URI from the Elestio service overview details. Copy and replace the variables carefully in the URI example provided above.

Prerequisites

While following this tutorial, you will need to have psql already installed; if not head over to https://www.postgresql.org/download/ and download it first.

Connecting to Hydra

Open your terminal and run the following command to connect to your Hydra database using the full connection URI:

psql HYDRA_URI

If the connection is successful, you’ll see output similar to this. Here it will show you the database you tried to connect to, which in this case is Elestio:

psql (17.4, server 14.13 (Debian 14.13-1.pgdg120+1))
SSL connection (protocol: TLSv1.3, cipher: TLS_AES_256_GCM_SHA384, compression: off, ALPN: none)
Type "help" for help.

elestio=#

To ensure you're connected correctly, run this command inside the psql prompt:

SELECT version();

You should receive output like the following:

version
---------------------------------------------------------------------------------------------------------------------
PostgreSQL 16.8 (Debian 16.8-1.pgdg120+1) on x86_64-pc-linux-gnu, compiled by gcc (Debian 12.2.0-14) 12.2.0, 64-bit
(1 row)

Connecting with pgAdmin

pgAdmin is a widely used graphical interface for Hydra that allows you to manage, connect to, and run queries on your databases with ease.

Variables

To connect using pgAdmin, you'll need the following connection parameters. When you deploy a Hydra service on Elestio, you also get a pgAdmin dashboard configured for you to use with these variables. These details are available in the Elestio service overview page:

Variable	Description	Purpose
`USER`	pgAdmin username	Identifies the pgAdmin user with access permission.
`PASSWORD`	pgAdmin password	Authentication key for the `USER`.

You can find these values in your Elestio project dashboard under Admin section.

Prerequisites

Make sure the Hydra service is correctly deployed on Elestio and you are able to access the Admin section like the one in the image above.

Setting Up the Connection

Launch pgAdmin from the Admin UI URL and log in with the credentials acquired in the steps before.
Click on "Create" and select "Server…" from the dropdown, or find Add New Server from the quick links
In the General tab:
- Enter a name for your connection (e.g., Trial pgAdmin Connection).
Go to the Connection tab and enter the following details:
- Host name/address: HOSTNAME
- Port: PORT
- Maintenance database: DATABASE
- Username: USERNAME
- Password: PASSWORD