Log management on Docker - docker

Question

I want to send STDOUT log from Docker container to fluentd.
But, when one container outputs access logs and error logs, logs are mixed.
example
# rails access log
2017-04-07 12:10:01 +0000 6a51e389e724: {"log":"I, [2017-04-07T12:10:01.825923 #7] INFO -- : Started GET \"/users/new\" for 172.21.0.1 at 2017-04-07 12:10:01 +0000","container_id":"6a51e389e724c67be4e714402b69da192db4a304cbfdf638594de6cff9774c23","container_name":"/app","source":"stdout"}
# rails error log
2017-04-07 12:10:01 +0000 6a51e389e724: {"container_id":"6a51e389e724c67be4e714402b69da192db4a304cbfdf638594de6cff9774c23","container_name":"/app","source":"stdout","log":"E, [2017-04-07T12:10:01.830039 #7] ERROR -- : Invoke logger error"}
# rails access log
2017-04-07 12:10:03 +0000 6a51e389e724: {"log":"I, [2017-04-07T12:10:01.825923 #7] INFO -- : Started POST \"/users/create\" for 172.21.0.1 at 2017-04-07 12:10:01 +0000","container_id":"6a51e389e724c67be4e714402b69da192db4a304cbfdf638594de6cff9774c23","container_name":"/app","source":"stdout"}
Can I add a label for each log type?
Please tell me if you have a good solution.
Thanks you and best regards.

Answer 1

As your app's access and error logs are sent to STDOUT of container, then you have no way to separate them by logging driver. As solution you can send access log to STDOUT, error log to STDERR of container, then later differentiate logs by "source" field of each json message (this can be done if you connect fluentd to elasticsearch+kibana).