Docker – How to send error-message to Graylog from Symfony-app, inside Kubernetes-cluster

A couple of docker-containers, running inside a Kubernetes Cluster:

PHP
Nginx
MySQL
Redis

There is a Graylog-instance (version 3), that listens to the stdout and stderr from those containers.

In the PHP-container, there is a Symfony-application, that uses Monolog to log errors, info, warnings and notices and what-not. Monolog usually logs to a file, defined in /config/packages/prod/monolog.yaml like this:

monolog:
    handlers:
        main:
            type: fingers_crossed
            action_level: error
            handler: nested
            excluded_http_codes: [404, 405]
        nested:
            type: rotating_file
            path: "%kernel.logs_dir%/%kernel.environment%.log"   # <-- Here
            level: debug

My operations-department said:

Graylog cannot see any files inside the containers. That is just how it works

My question

How do I set it up, so all my errors, warnings, notices, info, etc., is to be found in Graylog?

Solution attempt 1: Get Monolog-logger to print to the console

I’ve tried doing all kinds of backflips in /config/packages/prod/monolog.yaml, to get code like this:

// src/Controller/YourController.php
namespace AppController;

use PsrLogLoggerInterface;
...

class YourController extends AbstractController
{
    public function yourAction(LoggerInterface $logger): Response
    {
        $logger->info('This is an informational log');
        return new Response('Check the logs!');
    }
}

to write logs to stdout or stderr. But nothing is printed in the stdout.

My (best) attempts:

        console:
            type:   console
            process_psr_3_messages: false
            channels: ['!event', '!doctrine', '!console']

        syslog_handler:
            type: syslog
            level: debug

Solution attempt 2: Just use error_log()

The error_log('my message')-function does output to the console. Yay!
It feels dumb though, that I have this huge logging-library (Monolog), when I in the end just use error_log() anyway.

Plus, I would like for all errors and warnings to be caught and sent to Graylog – and not just my own inserted error_log-statements.

Another part of this is that this is an example of my output, when I use error_log():

projectname-php-1         | NOTICE: PHP message: ZZZ ErrorLogStatement: Error.log().
projectname-nginx-1       | 2023/09/22 12:56:17 [error] 10#10: *20 FastCGI sent in stderr: "PHP message: ZZZ ErrorLogStatement: Error.log()" while reading response header from upstream, client: 172.20.0.1, server: symfony.local, request: "GET /my-custom-endpoint?test_case=all_logs HTTP/1.1", upstream: "fastcgi://172.20.0.5:9000", host: "127.0.0.1:8200"
projectname-nginx-1       | 172.20.0.1 - - [22/Sep/2023:12:56:17 +0000] "GET /my-custom-endpoint?test_case=all_logs HTTP/1.1" 200 35 "-" "PostmanRuntime/7.32.3" "-"
projectname-php-1         | 172.20.0.6 -  22/Sep/2023:12:56:02 +0000 "GET /index.php" 200

Which means that both my Nginx-container and my PHP-container outputs the error, which adds a lot of redundant lines in my Graylog. I can filter these, but still! It’s messy.

Solution attempt 3: "Link" my error-log to stdout

I found this suggestion here: Make a Docker application write to stdout.

Which would be to "link" the rotating error-log file, to stdout (and then maybe remove the rotating of that file).

So I tried to run this:

ln -sf /dev/stdout /var/www/docroot/var/log/my-log-file.log

But I ran into this error:

The stream or file: "/var/www/docroot/var/log/prod-2023-09-22.log" could not be opened in append mode: failed to open stream: No such file or directory.

And even if I got that to work… It seems hacky and not like the right approach. So I stopped trying to get this to work.

Solution attempt 4: Send errors from Monolog to Graylog via it’s API

This would be the ideal solution. I was just hoping for a simpler solution.
But this is what I’m fiddling with now.