Health check intermittently fails during repeated PDF conversions #1648

Context

Our application uses Gotenberg to generate PDF files from DOCX documents.

In some cases, the application needs to generate a large number of PDFs sequentially. Before each conversion, it performs a request to the /health endpoint to check that the Gotenberg service is still available.

Description

When generating PDFs sequentially, the /health endpoint intermittently fails after several conversions, even though the Gotenberg service is still available.

The issue usually occurs after around 10–15 PDF conversions.

The PDF conversions themselves are performed sequentially: I wait for a PDF conversion to complete before starting the next one.

Reproduction

I tested the following Gotenberg versions:

8.28: issue not reproducible
8.29 → 8.36: issue reproducible

A minimal reproduction script is provided below.

The reproduction script assumes that a Gotenberg service is available at http://pdf:3000. The DOCX file used for the conversion is attached here: input.docx.

<?php

require_once 'External/autoload.php';

use GuzzleHttp\Client;

$client = new Client();
$url = 'http://pdf:3000';
$file = __DIR__ . '/input.docx';

for ($i = 1; $i <= 100; $i++) {
    echo "$i: health check... ";

    try {
        $client->get("$url/health", ['timeout' => 30]);
        echo "OK\n";

        $client->post("$url/forms/libreoffice/convert", [
            'multipart' => [[
                'name' => 'files',
                'contents' => fopen($file, 'r'),
                'filename' => 'file.docx',
            ]],
        ]);

        echo "   conversion OK\n";
    } catch (\Throwable $e) {
        echo "FAILED\n";
        echo $e::class . ': ' . $e->getMessage() . "\n";
        exit(1);
    }
}

Expected behavior

The /health endpoint should consistently return a successful response while the Gotenberg service is available, including when PDF conversions are performed sequentially.

Actual behavior

After several PDF conversions, the /health request can fail even though the Gotenberg service is still available.

The issue is intermittent, but typically occurs after around 10–15 conversions.

Adding a retry around the /health request allows the process to continue successfully, but it also forces us to wait for a potentially unnecessary amount of time before retrying.

Adding a sleep between PDF conversions does not appear to improve the situation.

Analysis

The issue appears to have been introduced in 8.29, since the same reproduction does not fail with 8.28 but does fail with versions up to 8.36.

The fact that retrying the /health request immediately succeeds makes me suspect a regression affecting the health check behavior under repeated conversion requests.

Do you know what might have changed in 8.29 that could explain this behavior? Is this a known issue?

Any feedback or insight would be greatly appreciated. Thank you very much for your help and for taking the time to look into this.