Level "100" is not defined, use one of: 100, 200, 250, 300

Pls describe why we need this change

I am also having this error, see attached screenshot.
My configuration: core 8.9.2, drupal/monolog 2.0.0-beta1 and monolog/monolog 2.1.0

The patched #2 fixes the error.

RTBC +1

The problem is they are defined as strings in the services file, but they should be defined as integers instead. The setLevel method does this in Monolog\Logger:

if (is_string($level)) {
  // Contains chars of all log levels and avoids using strtoupper() which may have
  // strange results depending on locale (for example, "i" will become "İ" in Turkish locale)
  $upper = strtr($level, 'abcdefgilmnortuwy', 'ABCDEFGILMNORTUWY');
  if (defined(__CLASS__.'::'.$upper)) {
    return constant(__CLASS__ . '::' . $upper);
  }

  throw new InvalidArgumentException('Level "'.$level.'" is not defined, use one of: '.implode(', ', array_keys(static::$levels)));
}

So it assumes it's a constant defined on the class instead of the log level we want. Please commit this for beta2.

Committed and pushed to 2.x, thanks!

I'm going to release a beta2.

The issue still exist in beta 2, See #6.

It does not, for me beta2 works fine without a patch. So if you still see the problem your probably not on beta2.

Seems that there is a different, possibly related error.

I'm seeing this:
Level "monolog.level.debug" is not defined, use one of: 100, 200, 250, 300, 400, 500, 550, 600

Checked the values on services.monolog.yml and they are integers, also checked the version in composer and I'm on beta 2.

"name": "drupal/monolog",
                "url": "https://git.drupalcode.org/project/monolog.git",
                "url": "https://ftp.drupal.org/files/projects/monolog-2.0.0-beta2.zip",
                "monolog/monolog": "^2.0.0"

Is a problem on my side?
Should I open a new bug, or it is related to the old one?

Still the error appears on beta2 version:

Level "monolog.level.debug" is not defined, use one of: 100, 200, 250, 300, 400, 500, 550, 600, DEBUG, INFO, NOTICE, WARNING, ERROR, CRITICAL, ALERT, EMERGENCY

Will find out the reason why it is appearing, if valid can reopen this bug.

This issue was reproducible only when using composer drupal/core and not while using drupal/core-recommended

So it should be related or because of some vendor library.

I had also encounter this issue after I updated to drupal 9.x.
The problem was that inside the site specific services.yml (Eg: monolog.services.yml) the configuration

services:
  monolog.handler.rotating_file:
    class: Monolog\Handler\RotatingFileHandler
    arguments: ['private://logs/debug.log', 10, '%monolog.level.debug%']

had "monolog.level.debug" instead of "%monolog.level.debug%".
Hope it helps.

#15 works... sort of.
It works AFTER monolog is installed, but it breaks on install/uninstall with the error:

You have requested a non-existent parameter "monolog.level.debug".

If I switch it back to 'monolog.level.debug', then I can install/uninstall.
This is causing some issues with deployments. I think this issue should be reopened.

UPDATE: Just figured out that combining patch from #2 and #15 fixes both the notice and install/uninstall.

I am having the issue when installing the module if I have handler defined like this:

services:
  monolog.handler.rotating_file:
    class: Monolog\Handler\RotatingFileHandler
    arguments: ['private://logs/drupal.log', 10, '%monolog.level.debug%']

The error I am getting
You have requested a non-existent parameter "monolog.level.debug".