symfony 5.3 logfile could not be opened in append mode: Failed to open stream (docker)

Question

I have a rotating Logfile configured with monolog, which worked like a charm and suddenly I get error messages stating that the file cannot be created, when the frontend is calling my symfony backend, which runs in a alpine docker container. Creating logfiles while running my phpunit tests is causing no trouble at all.

This is my monolog configuration, which didn't change:

monolog:
    handlers:
        frontend:
            type: rotating_file
            path: "%kernel.logs_dir%/%kernel.environment%.frontend.log"
            level: error
            channels: [ frontend ]
            max_files: 3
        main:
            type: rotating_file
            path: "%kernel.logs_dir%/%kernel.environment%.log"
            level: debug
            channels: [ "!event", "!frontend", "!deprecation"  ]
            max_files: 3
        console:
            type: console
            process_psr_3_messages: false
            channels: [ "!event", "!doctrine", "!console", "!frontend", "!deprecation" ]

What I did was disabling sessions, which should have no influence on whether the system is able to create a file for writing.

Why can my server no longer write logfiles?

My permissions for my log folder are increased to 777 and the server runs as "root" in it's container:

e9dffe459185:/var/www/var# ll
total 8
drwxrwxr-x    6 root     root           192 Jul 22 15:07 ./
drwxr-xr-x   51 root     root          1632 Jul 23 10:16 ../
drwxrwxr-x    4 root     root           128 Jul 23 11:01 cache/
drwxrwxrwx    3 root     root            96 Jul 23 11:02 log/

Answer 1

Looks like the problem was fixed with an update of monolog:

Updating dependencies
Lock file operations: 0 installs, 1 update, 0 removals
  - Upgrading monolog/monolog (2.3.1 => 2.3.2)
Writing lock file
Installing dependencies from lock file (including require-dev)
Package operations: 0 installs, 1 update, 0 removals
  - Downloading monolog/monolog (2.3.2)
  - Upgrading monolog/monolog (2.3.1 => 2.3.2): Extracting archive

Looks like version 2.3.1 was buggy. Since the upgrade I don't have further problems.