The "official" PHP docker images use the same method for FPM (output redirection) to get worker logs into stdout so they can be ingested: https://github.com/docker-library/php/blob/d6838d8e45f6356d867dbc8ff8b3513492cba500/7.3/buster/fpm/Dockerfile#L230

This is also what we're using in our own MediaWiki PHP images that use the above as base.

This also relies on FPM's catch_workers_output and decorate_workers_output options to redirect workers' stdout and stderr into the main error log FPM is configured to use, without messing up the formatting of the messages logged by applayer. However, the latter param is only available from PHP 7.3 onwards.

https://pracucci.com/php-on-kubernetes-application-logging-via-unix-pipe.html provides two options for how php-fit could be set up to get the logs from worker processes.

The first option has a lot of drawbacks. The second option is what I proposed in my Gerrit comment.

Another option which occurs to me is to use a higher-numbered FD.

# /opt/php7.3/sbin/php-fpm -F 4>&1
[23-Sep-2020 10:05:20] NOTICE: fpm is running, pid 47854
[23-Sep-2020 10:05:20] NOTICE: ready to handle connections

# lsof -p 47855
...
php-fpm 47855 www-data    0u   CHR                1,3      0t0       5 /dev/null
php-fpm 47855 www-data    1u   CHR                1,3      0t0       5 /dev/null
php-fpm 47855 www-data    2u   CHR                1,3      0t0       5 /dev/null
php-fpm 47855 www-data    4u   CHR              136,2      0t0       5 /dev/pts/2

PHP does not close higher numbered FDs, it lets them be inherited by the worker process. Stdout is duplicated to FD 4, so when the worker writes to FD 4, it will appear to Kubernetes as if it came from stdout. I used FD 4 in this example to avoid conflict with limit.sh which uses FD 3 for a similar purpose.

@Joe says that application logs can go to logstash while php-fpm error logs will go to k8s. I want to say that the simplest way to send application logs to logstash is to use the logToClient option, which serializes log entries and sends them back to MediaWiki. This way, the configuration stays the same, and we don't need to port MediaWiki's custom logstash formatter. You lose log messages generated after the response is sent, but currently that's just temporary directory teardown failures which probably don't matter. For php-fpm error logs, we can start it with "php-fpm -F 2>&1", then logs go to php-fpm's stderr which is redirected to k8s's stdout.