[COUCHDB-2970] config:set("log","level",...) fails to change lager backend levels

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 2.0.0
• Component/s: Logging
• Assignee: Jay Doane
• Reporter: Jay Doane
• Created: 17/Mar/16 00:29
• Updated: 17/Mar/16 16:50
• Resolved: 17/Mar/16 09:27

Description

The following remsh session shows that at first, both config log level and lager_file_backend levels are the same (info), but after we use config to change the level to notice, the lager level remains at info:

(cloudant@db1.v)26> config:get("log","level").
"info"
(cloudant@db1.v)27> gen_event:which_handlers(lager_event).
[{lager_file_backend,"/var/log/cloudant/cloudant.log"},
 lager_backend_throttle]
(cloudant@db1.v)28> lager:get_loglevel({lager_file_backend,"/var/log/cloudant/cloudant.log"}).
info
(cloudant@db1.v)29> config:set("log","level","notice",false).
ok
(cloudant@db1.v)30> lager:get_loglevel({lager_file_backend,"/var/log/cloudant/cloudant.log"}).
info

The problem occurs because https://github.com/apache/couchdb-couch-log-lager/blob/master/src/couch_log_lager.erl#L67 obtains the handlers from application:get_env(lager, handlers), which returns the a structure defined in sys.config, but it should use gen_event:which_handlers(lager_event), which returns the actual list of handlers:

(cloudant@db1.v)31> application:get_env(lager, handlers).                                
{ok,[{lager_file_backend,
         [{file,"/var/log/cloudant/cloudant.log"},
          {formatter,lager_default_formatter},
          {formatter_config,
              [date," ",time," [",severity,"] ",node," ",pid," ",message,
               "\n"]}]}]}
(cloudant@db1.v)32> gen_event:which_handlers(lager_event).                               [{lager_file_backend,"/var/log/cloudant/cloudant.log"},
 lager_backend_throttle]