Logging Design

[rumpelsepp]

I will update this from time to time.

Currently we use a homegrown logging implementation which served its purpose very well, but we should really move to an implementation which uses python's logging module. Using this we just gain the ability to log to multiple files and the console at once. For this I started #191.

We also have a specification which defines all the JSON fields in the log records. This is important, since a design goal of gallia is comprehensive and machine readable logging. I am unhappy with the current spec, thus I suggest a change.

Penlog

• Drop all the formatting specs. The specification should only specify what is in the JSON log record and what is its purpose.
• Add a version field and set it to version 2 for the current spec.
• Drop the message type. There is already a tags field. We should use this instead and define some special tags for gallia that the formatter could use; for instance result, read, write, ….
• Specify that the ISO timestamp must contain timezone information. We discussed a lot that our database logging should store timestamps; thus let's be consistent and enforce this in the logging as well.
• Provide a user friendly interface for changing the log level: -v for DEBUG and -vv for TRACE.

Open for discussion

• Delete PENLOG_LOGLEVEL?
• Which loglevel in the logfile? Always TRACE? Configurable?