API call with max number of retries and exponential backoff in PHP

exponential-backoff.php

<?php

$retries = 0;  // Init the retries variable
$maxRetries = 5;  // Means we try max 6 times
$retry = false;  // Should we retry or not?
$initialWait = 1.0;  // Initial wait time in seconds

try {
    do {
        // If it is not the first try, calculate exponential backoff and wait
        if ($retries > 0) {
            $waitTime = pow(2, $retries);
            sleep($initialWait * $waitTime);
        }

        // Call the "risky" API function
        $result = callExternalAPI();  // Here we assume this function returns an HTTP status code if it fails

        // Retry if server error (5XX) or throttling error (429) occurred
        if ($result == 500 || $result == 503 || $result == 429) {
            $retry = true;
        } else {
            $retry = false;
        }

    } while ($retry && ($retries++ < $maxRetries));
} catch (Exception $e) {
    throw $e;
}

// If you get to here, your API call has succeeded