Description:
------------
On Dockerfile, the official distribution of php have this configuration : 

[global]
error_log = /proc/self/fd/2 

; if we send this to /proc/self/fd/1, it never appears
access.log = /proc/self/fd/2

seems related to this configuration : 

catch_workers_output boolean
Redirect worker stdout and stderr into main error log. If not set, stdout and stderr will be redirected to /dev/null according to FastCGI specs. Default value: no.

With this configuration, we can't really parse log file (or monitor log) because access log & php fpm stdout & error log in not separated.

see dockerfile maintainer response : https://github.com/docker-library/php/issues/358#issuecomment-271033464

So there is 2 issues here : 
- access log won't write to docker special files : /dev/stdout
- fpm main log with catch_workers_output = yes output stdout & stderr on the same log file, maybe we need a new configuration options in order to have workers output error to stderr & fpm master process std*** to std***