wait-for-elasticsearch.php

#!/usr/bin/env php
<?php

declare(strict_types=1);

namespace WaitForElasticsearch;

use InvalidArgumentException;
use UnexpectedValueException;
use function curl_close;
use function curl_exec;
use function curl_getinfo;
use function curl_init;
use function error_log;
use function getenv;
use function is_string;
use function microtime;
use function sprintf;
use function usleep;
use const CURLINFO_HTTP_CODE;
use const CURLOPT_HEADER;
use const CURLOPT_RETURNTRANSFER;
use const CURLOPT_TIMEOUT_MS;
use const CURLOPT_URL;

// Note: this is a dependency-less file that only relies on ext-curl to function. We do not want any dependencies in
//       here, since the system may not yet be in functional state at this stage.
(static function () : void {
    $elasticsearch = getenv('ELASTICSEARCH_URL');

    if (! is_string($elasticsearch)) {
        throw new InvalidArgumentException('Missing "ELASTICSEARCH_URL" environment variable');
    }

    $timeLimit     = (float) (getenv('ELASTICSEARCH_WAIT_TIMEOUT_SECONDS') ?: 60.0);
    $retryInterval = (int) ((((float) getenv('ELASTICSEARCH_RETRY_INTERVAL_SECONDS')) ?: 0.5) * 1000000);
    $start         = microtime(true);
    $elapsedTime   = static function () use ($start) : float {
        return microtime(true) - $start;
    };
    $remainingTime = static function () use ($elapsedTime, $timeLimit) : float {
        return $timeLimit - $elapsedTime();
    };

    while ($remainingTime() > 0) {
        $curl = curl_init();

        // @see https://www.elastic.co/guide/en/elasticsearch/reference/current/cluster-health.html
        curl_setopt($curl, CURLOPT_HEADER, 0);
        curl_setopt($curl, CURLOPT_TIMEOUT_MS, 500);
        curl_setopt($curl, CURLOPT_RETURNTRANSFER, true);
        curl_setopt(
            $curl,
            CURLOPT_URL,
            $elasticsearch . sprintf('/_cluster/health?wait_for_status=yellow&timeout=%ds', (int) $timeLimit)
        );

        $response = curl_exec($curl);

        $errorCode    = curl_errno($curl);
        $errorMessage = curl_error($curl);
        $statusCode   = curl_getinfo($curl, CURLINFO_HTTP_CODE);

        curl_close($curl);

        if ($errorCode === 0) {
            /** @noinspection ForgottenDebugOutputInspection */
            error_log(sprintf('ElasticSearch connection succeeded after %.2f seconds', $elapsedTime()));

            if ($statusCode === 200) {
                /** @noinspection ForgottenDebugOutputInspection */
                error_log(sprintf(
                    'ElasticSearch status is (at least) yellow after %.2f seconds with response: %s',
                    $elapsedTime(),
                    $response
                ));

                return;
            }

            /** @noinspection ForgottenDebugOutputInspection */
            error_log(sprintf(
                'ElasticSearch status is pending after %.2f seconds with response code %d',
                $elapsedTime(),
                $statusCode
            ));
        }

        if ($errorCode !== 0) {
            /** @noinspection ForgottenDebugOutputInspection */
            error_log(sprintf(
                'Failed to contact ElasticSearch: curl error "%s", code %d, retrying for another %.2f seconds',
                $errorMessage,
                $errorCode,
                $remainingTime()
            ));
        }

        usleep($retryInterval);
    }

    throw new UnexpectedValueException(sprintf('Failed to connect to Elasticsearch after %.2f seconds', $elapsedTime()));
})();