diff --git a/README.md b/README.md
index 2cd783b..8ea464d 100644
--- a/README.md
+++ b/README.md
@@ -72,7 +72,13 @@ Deployment
    3. Run: `kgi-processing --connection-string=postgres://${POSTGRES_USER}:${POSTGRES_PASSWORD}@${POSTGRES_HOST}:${POSTGRES_PORT}/${POSTGRES_DB}?sslmode=disable`
 6. Run `api`
    1. Navigate to wherever you copied `api` to
-   2. Run: `npm run start`
+   2. Set the following environment variables:
+      1. POSTGRES_USER=username - which is the username for database connection.
+      2. POSTGRES_PASSWORD=password - which is the password for database connection.
+      3. POSTGRES_DB=database-name - which is the database to be used.
+      4. POSTGRES_HOST=database.example.com (optional) - which is the host of the database server (default: localhost).
+      5. POSTGRES_PORT=5432 (optional) - which is the port for database connection (default: 5432).
+   3. Run: `npm run start`
 7. Run `web`
    1. Navigate to wherever you copied `web` to
    2. Run: `npm install -g serve`
diff --git a/api/src/database.ts b/api/src/database.ts
index 236f27b..acc4cb7 100644
--- a/api/src/database.ts
+++ b/api/src/database.ts
@@ -2,11 +2,38 @@ import pg from "pg";
 import {AppConfig, Block, BlockHashById, BlocksAndEdgesAndHeightGroups, Edge, HeightGroup} from "./model";
 import { packageVersion } from "./version.js";
 
+/* database environment. */
+const postgres_user = process.env.POSTGRES_USER;
+const postgres_password = process.env.POSTGRES_PASSWORD;
+const postgres_host = process.env.POSTGRES_HOST ?? "localhost";
+const postgres_port = process.env.POSTGRES_PORT ?? "5432";
+const postgres_database = process.env.POSTGRES_DB;
+
+/* missing check. */
+if (!postgres_user) {
+    console.log("The POSTGRES_USER environment variable is required");
+    process.exit(1);
+}
+if (!postgres_password) {
+    console.log("The POSTGRES_PASSWORD environment variable is required");
+    process.exit(1);
+}
+if (!postgres_database) {
+    console.log("The POSTGRES_DB environment variable is required");
+    process.exit(1);
+}
+
 export default class Database {
     private pool: pg.Pool;
 
     constructor() {
-        this.pool = new pg.Pool();
+        this.pool = new pg.Pool({
+            user: postgres_user,
+            password: postgres_password,
+            host: postgres_host,
+            port: parseInt(postgres_port),
+            database: postgres_database,
+        });
     }
 
     withClient = async (func: (client: pg.PoolClient) => Promise<void>) => {
diff --git a/docker-compose.yaml b/docker-compose.yaml
index 511b68d..af7b9e7 100644
--- a/docker-compose.yaml
+++ b/docker-compose.yaml
@@ -25,11 +25,9 @@ services:
     depends_on:
       - postgres
     environment:
-      - PGUSER=${POSTGRES_USER}
-      - PGPASSWORD=${POSTGRES_PASSWORD}
-      - PGDATABASE=${POSTGRES_DB}
-      - PGHOST=localhost
-      - PGPORT=5432
+      - POSTGRES_USER=${POSTGRES_USER}
+      - POSTGRES_PASSWORD=${POSTGRES_PASSWORD}
+      - POSTGRES_DB=${POSTGRES_DB}
       - API_PORT=${API_PORT}
     command:
       - "npm"