I’m building a docker image for a Symfony application. In this image, I want to stream the Symfony logs to stdout. So, similar to how nginx logs are configured, I added this line to my Dockerfile:
ln -sf /dev/stdout /var/www/project/app/logs/prod.log
Inside the container, I can see this:
$ ls /var/www/project/app/logs/ -l total 12 -rw-r--r-- 1 501 games 4473 Jul 21 08:36 dev.log lrwxrwxrwx 1 501 games 11 Jul 21 08:35 prod.log -> /dev/stdout
However, the app throws following error:
PHP Fatal error: Uncaught exception ‘UnexpectedValueException’ with message ‘The stream or file “/var/www/project/app/logs/prod.log” could not be opened: failed to open stream: No such file or directory’ in /var/www/project/app/cache/prod/classes.php:5808
Stack trace:
#0 /var/www/project/app/cache/prod/classes.php(5746): MonologHandlerStreamHandler->write(Array)
#1 /var/www/project/app/cache/prod/classes.php(5917): MonologHandlerAbstractProcessingHandler->handle(Array)
#2 /var/www/project/app/cache/prod/classes.php(6207): MonologHandlerFingersCrossedHandler->handle(Array)
#3 /var/www/project/app/cache/prod/classes.php(6276): MonologLogger->addRecord(500, ‘Fatal Error: Un…’, Array)
#4 /var/www/project/app/cache/prod/classes.php(1978): MonologLogger->log(‘critical’, ‘Fatal Error: Un…’, Array)
#5 /var/www/project/app/cache/prod/classes.php(2034): SymfonyComponentDebugErrorHandler->handleException(Object(SymfonyComponentDebugExceptionFatalErrorException), Array)
#6 [internal function]: SymfonyComponentDebugE in /var/www/project/app/cache/prod/classes.php on line 5808
Any suggestions ?
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Answer
With the help of Monolog, it is very easy to send logs to stdout/stderr. My examples are using stderr, but I think it’s the same with stdout.
Instead of defining a log file you just enter the preferred stream path
path: "php://stderr"
BUT you are not done yet. You also have to configure PHP accordingly. The workers have to catch the output of their processes and log this output again to their stderr.
PHP Configuration
#/etc/php/7.0/fpm/php-fpm.conf error_log = /proc/self/fd/2 #/etc/php/7.0/fpm/pool.d/www.conf catch_workers_output = yes
Symfony Configuration
# app/config/config_prod.yml monolog: handlers: main: type: fingers_crossed action_level: error handler: nested nested: type: stream path: "php://stderr" level: debug console: type: console
If you are using any process control system in a fat docker container you have to make sure that this system also logs to stdout (or stderr).
Example with supervisor:
[supervisord] nodaemon=true ;@see http://blog.turret.io/basic-supervisor-logging-with-docker/ ;we need the output from the controlled processes ;but this is only possible with lowered loglevel loglevel=debug
All in all make sure that:
- The application logs to stdout/stderr
- PHP catches workers output and logs to stderr
- optional: any process control system has to forward output of managed processes to stdout/stderr