Core Concepts →

📐 Configuration Schema

At its heart, App Config.json uses a strict JSON schema to define, validate, and enforce configuration structure across your application. Every config file is validated against a schema before deployment, preventing runtime errors caused by malformed or missing keys.

schema.json

{
  "$schema": "https://appconfig.json/schemas/v3",
  "type": "object",
  "required": ["app", "features"],
  "properties": {
    "app": {
      "type": "object",
      "properties": {
        "name": { "type": "string" },
        "port": { "type": "integer", "minimum": 1024 }
      }
    }
  }
}
                    

ℹ️ Schema Enforcement

Invalid configurations are rejected at the API gateway level. Your application will never receive a malformed payload.

🌍 Environment Overrides

App Config.json supports layered configuration. Define a base configuration, then apply environment-specific overrides without duplicating entire files. This follows the 12-factor app methodology for environment separation.

config.json

{
  "database": {
    "host": "localhost",
    "port": 5432,
    "pool_size": 5
  },
  // Environment overrides are merged at runtime
  "environments": {
    "production": {
      "database": {
        "host": "db.prod.internal",
        "pool_size": 25
      }
    }
  }
}
                    

💡 Pro Tip

Use .env variables inside config values with {{ENV_VAR}} syntax. They are resolved server-side before delivery.

⚡ Real-Time Sync

Configuration updates propagate to all connected instances via WebSocket channels with fallback to long-polling. Your application receives delta updates, not full payloads, minimizing bandwidth and latency.

When a config is published:

Server validates & encrypts the payload
Diff is calculated against the active version
Updates are broadcast to subscribed clients
Clients acknowledge receipt within ~50ms

⚠️ Network Resilience

If a client drops connection, it will automatically fetch the latest config on reconnection. No state is lost.

🔄 Versioning & Rollback

Every configuration change creates an immutable, timestamped version. You can inspect diffs, audit changes, and instantly rollback to any previous state without redeploying your application.

Terminal

$ appconfig versions list
✅ v12.4.1  (active)  published 2h ago by @dev_ops
📦 v12.4.0  published 1d ago by @sarah_k
📦 v12.3.9  published 3d ago by @ci_pipeline

$ appconfig rollback v12.4.0
🔙 Rolling back to v12.4.0...
✅ All 42 instances updated successfully.
                    

🔐 Secrets Management

Sensitive values (API keys, database passwords, JWT secrets) are stored separately from configuration and never logged or cached in plaintext. They are encrypted at rest using AES-256-GCM and transmitted via TLS 1.3.

Access is controlled via role-based policies. You can define who can view, edit, or inject secrets into specific environments.

📦 SDK Integration

Our first-party SDKs handle connection management, retry logic, and hot-reloading automatically. Supported runtimes include Node.js, Python, Go, Java, and Rust.

app.js (Node.js)

import { ConfigClient } from '@appconfig/sdk';

const client = new ConfigClient({
  project: 'my-app',
  environment: process.env.'NODE_ENV',
  apiKey: process.env.'AC_JWT'
});

await client.connect();

client.on('change', (config) => {
  console.log('Config updated:', config.features);
  app.reloadMiddleware(config);
});
                    