HTTP 503 Service Unavailable

What is HTTP 503 Service Unavailable?

The 503 (Service Unavailable) status code indicates that the server is currently unable to handle the request due to a temporary overload or scheduled maintenance which will likely be alleviated after some delay. The response should include a Retry-After header indicating when the service is expected to be available again.

Common Use Cases

• Server maintenance mode
• Traffic overload or spikes
• Application deployment in progress
• Resource exhaustion (connections, threads)

// Laravel - maintenance mode (php artisan down)
// Automatically returns 503 with Retry-After

// Custom 503 for traffic spikes
return response()->json([
    'error' => 'Service unavailable',
    'retry_after_seconds' => 30,
], 503)
->header('Retry-After', 30);