Write a recursive exponential backoff service (ping) check.

expo.js

const http = require('http');

const RetryIntervals = [500, 1000, 4000];
const retryTries = 4;

function pingService(retryInterval, retryTry) {
	if(retryTry >= retryTries) {
		console.log(`ping not ok after ${retryTries} retries, giving up.`);
		return;
	}

	const opts = {
		host: 'sample.com',
		path: '/zzz'
	};

	const retry = function(retryInterval) {
		console.log(`retry after ${RetryIntervals[retryInterval]} seconds...`);
		setTimeout(function() {
			const newRetry = (retryInterval + 1 < RetryIntervals.length) ? retryInterval + 1 : retryInterval;
			pingService(newRetry, retryTry+1);
		}, RetryIntervals[retryInterval]);
	};

	const req = http.request(opts, (res) => {
		if(res.statusCode === 200) {
			console.log('ping ok!');
		}
		else {
			console.log('ping not ok!');
			retry(retryInterval);
		}
	});
	req.on('error', (e) => {
		console.log(`problem with request: ${e.message}`);
		retry(retryInterval);
	});
	req.end();
}


pingService(0, 0);