clear gitlab container registry image in gitlab.com ... taken from https://gitlab.com/gitlab-org/gitlab-ce/issues/25322#note_54099611

clear-gitlab-container-registry.php

<?php
/**
 * Created by: pckofstad
 */

$GITLAB_CI_TOKEN=
$REPO = "{user}/{project}
$REGISTRY_ID = 11111; // only way i found this was to inspect the calls done from the webpage

$TAGS_TO_WHITELIST = ['dev', 'master'];
$AGE_OF_CONTAINERS_TO_KEEP = '1 day';   // using php strtotime function
$BASE_URL = 'https://gitlab.com/';

$DEBUG = false;


// Variables
$FETCH_HEADER_URL = $BASE_URL . $REPO . '/container_registry';
$FETCH_TAGS_URL = $BASE_URL . $REPO . '/registry/repository/' . $REGISTRY_ID . '/tags?format=json';
$TAG_DELETE_URL = $BASE_URL . $REPO . '/registry/repository/' . $REGISTRY_ID . '/tags/';

$header = [];

// Setup header that is needed to do delete tag calls.
function setupProperHeaders()
{
    global $GITLAB_CI_TOKEN, $header, $FETCH_HEADER_URL;

    $ch = curl_init();
    $options = [
        CURLOPT_URL => $FETCH_HEADER_URL,
        CURLOPT_RETURNTRANSFER => 1,
        CURLOPT_HEADER => 1,
        CURLOPT_HTTPHEADER => ['PRIVATE-TOKEN: ' . $GITLAB_CI_TOKEN]
    ];
    curl_setopt_array($ch, $options);
    $response = curl_exec($ch);

    $header_size = curl_getinfo($ch, CURLINFO_HEADER_SIZE);
    $header_text = substr($response, 0, $header_size);
    $body_text = substr($response, $header_size);
    curl_close($ch);

    $headers = [];
    foreach (explode("\r\n", $header_text) as $i => $line) {
        if ($i === 0) {
            $headers['http_code'] = $line;
        } else {
            $data = explode(': ', $line);
            if (count($data) == 2) {
                list ($key, $value) = $data;
                $headers[$key] = $value;
            }
        }
    };
    preg_match_all('/<meta *.*csrf-token*.* content="(.*|\n*?)" * \/>/'
        , $body_text
        , $regexOut
        , PREG_PATTERN_ORDER
        , 0);

    $X_CSRF_TOKEN = $regexOut[1][0];

    $COOKIE = $headers['Set-Cookie'];
    $header = [
        'X-CSRF-Token: ' . $X_CSRF_TOKEN,
        'Accept: application/json, text/plain, */*',
        'Cookie: ' . $COOKIE,
        'X-Requested-With: XMLHttpRequest',
        'PRIVATE-TOKEN: ' . $GITLAB_CI_TOKEN
    ];
}

// Wrapper for curl requests
function curlWrapper($url, $header = [], $asDeleteRequest = false)
{
    global $DEBUG;

    $ch = curl_init();
    $options = [
        CURLOPT_URL => $url,
        CURLOPT_USERAGENT => 'Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; .NET CLR 1.1.4322)',
        CURLOPT_RETURNTRANSFER => 1,
        CURLOPT_CONNECTTIMEOUT => 15,
        CURLOPT_TIMEOUT => 5,
    ];
    curl_setopt_array($ch, $options);

    if ($asDeleteRequest) {
        curl_setopt($ch, CURLOPT_CUSTOMREQUEST, "DELETE");
    }

    if (!empty($header)) {
        curl_setopt($ch, CURLOPT_HTTPHEADER, $header);
    }

    if (!empty($username)) {
        curl_setopt($ch, CURLOPT_USERPWD, $username . ':' . $password);
    }

    $data = curl_exec($ch);
    $httpcode = curl_getinfo($ch, CURLINFO_HTTP_CODE);

    if (empty($data) && $DEBUG) {
        $error = curl_error($ch);
        $errorno = curl_errno($ch);
        echo PHP_EOL . 'ERROR - ' . $error . ' --- ' . $errorno;
    }
    curl_close($ch);

    if ($httpcode >= 200 && $httpcode < 300) {
        return $data;
    }
    return false;
}

// taken from http://jeffreysambells.com/2012/10/25/human-readable-filesize-php
function human_filesize($bytes, $decimals = 2)
{
    $size = array('B', 'kB', 'MB', 'GB', 'TB', 'PB', 'EB', 'ZB', 'YB');
    $factor = floor((strlen($bytes) - 1) / 3);
    return sprintf("%.{$decimals}f", $bytes / pow(1024, $factor)) . @$size[$factor];
}

// --- Script startes here --- //

$i = 0;
$all_tags = [];
echo PHP_EOL . "Retrieving tags";
while (true || $i > 100) {
    $i += 1;

    $retrived_tags = json_decode(curlWrapper($FETCH_TAGS_URL . '&page=' . $i,
        ['PRIVATE-TOKEN: ' . $GITLAB_CI_TOKEN]));

    if (empty($retrived_tags)) {
        break;
    }

    echo '.';
    $all_tags = array_merge($all_tags, $retrived_tags);
}


if (!empty($all_tags)) {
    echo PHP_EOL . "Registry list fetched " . count($all_tags) . ' found';
}

if (count($all_tags) == 0) {
    echo " - Nothing found" . PHP_EOL;
    return;
}

setupProperHeaders();
$newest_timestamp_to_keep = strtotime('-' . $AGE_OF_CONTAINERS_TO_KEEP);

$deletedCount = 0;
$total_size = 0;
foreach ($all_tags as $tag) {
    if (empty($tag->name) || in_array($tag->name, $TAGS_TO_WHITELIST)) {
        continue;
    }

    $tag_date = date_create_from_format('Y-m-d\TH:i:s.u+T', $tag->created_at);
    $test = empty($tag->created_at) ? '' : $tag_date->getTimestamp();
    if (!empty($tag->created_at) && $newest_timestamp_to_keep < $tag_date->getTimestamp()) {
        continue;
    }


    echo PHP_EOL . "Trying to delete " . $tag->name . ' - created at ' . $tag->created_at;
    $call = curlWrapper($TAG_DELETE_URL . $tag->name, $header, true);

    // returns empty call if sucess, null if failed
    if ($call == '') {
        echo " - deleted ";
        $deletedCount++;
        $total_size += $tag->total_size;
    }
}

if ($deletedCount == 0) {
    echo PHP_EOL . PHP_EOL . "None of the tags was set to be deleted" . PHP_EOL;
} else {
    echo PHP_EOL . PHP_EOL . "You deleted: " . $deletedCount . " - Cleaned up: " . human_filesize($total_size) . PHP_EOL;
}

// end for script
?>