503 שירות אינו זמין

HTTP/1.1 503 Service Unavailable
Retry-After: 3600
Content-Type: application/json

{
    "error": "Service Unavailable",
    "message": "We're performing scheduled maintenance. Service resumes in 1 hour.",
    "retryAfter": 3600
}

HTTP/1.1 503 Service Unavailable
Retry-After: Wed, 21 Oct 2024 16:00:00 GMT

{
    "error": "Maintenance in Progress",
    "message": "Scheduled maintenance until 4:00 PM.",
    "resumeTime": "2024-10-21T16:00:00Z"
}

HTTP/1.1 503 Service Unavailable
Retry-After: 30

{
    "error": "Service Overloaded",
    "message": "Too many concurrent requests. Try again in 30 seconds."
}

app.get('/api/data', async function(request, response) {
    try {
        const data = await database.query('SELECT * FROM data');
        response.json(data);
    }
    catch(error) {
        response.status(503)
            .set('Retry-After', '60')
            .json({
                error: 'Service Unavailable',
                message: 'Database temporarily unavailable'
            });
    }
});

let ready = false;
let shuttingDown = false;

app.use(function(request, response, next) {
    if(!ready || shuttingDown) {
        return response.status(503).json({
            error: ready ? 'Shutting Down' : 'Starting Up',
            message: 'Service temporarily unavailable'
        });
    }
    next();
});

Retry-After: 60

Retry-After: Wed, 21 Oct 2024 16:00:00 GMT

const fs = require('fs');

app.use(function(request, response, next) {
    if(fs.existsSync('/var/www/maintenance.flag')) {
        const config = JSON.parse(fs.readFileSync('/var/www/maintenance.flag'));
        return response.status(503)
            .set('Retry-After', config.retryAfter)
            .json({
                error: 'Maintenance in Progress',
                message: config.message
            });
    }
    next();
});

echo '{"retryAfter": 3600, "message": "Scheduled maintenance"}' > /var/www/maintenance.flag

rm /var/www/maintenance.flag

async function fetchWithRetry(url, maxRetries = 3) {
    for(let attempt = 0; attempt < maxRetries; attempt++) {
        const response = await fetch(url);

        if(response.status !== 503) {
            return response;
        }

        const retryAfter = response.headers.get('Retry-After');
        let waitTime;

        if(retryAfter && /^\d+$/.test(retryAfter)) {
            waitTime = parseInt(retryAfter) * 1000;
        }
        else if(retryAfter) {
            waitTime = new Date(retryAfter).getTime() - Date.now();
        }
        else {
            waitTime = Math.pow(2, attempt) * 1000; // Exponential backoff
        }

        await new Promise(function(resolve) {
            setTimeout(resolve, waitTime);
        });
    }

    throw new Error('Service unavailable after retries');
}

app.get('/health', async function(request, response) {
    const checks = {
        database: await pingDatabase(),
        cache: await pingCache()
    };

    const healthy = Object.values(checks).every(Boolean);

    response.status(healthy ? 200 : 503)
        .set(healthy ? {} : { 'Retry-After': '60' })
        .json({ status: healthy ? 'healthy' : 'unhealthy', checks });
});