Use custom logger in fab-backend

[Holzchopf]

Introduction

Acceptance Criteria

• Define log level at application/container start-up time (error, info, debug, ...)
• Log with custom format (incl. timestamp) that can be parsed with standard tooling https://betterstack.com/community/comparisons/logstash-alternatives/#1-better-stack

Open Questions

If possible, let logger handle the evaluation of the log level, avoid clustering the code with ifs if possible.

Context

#34

Implementation

Backend should know different log levels, e.g. in dev all notices are relevant, in prod only warnings and errors. Plus, errors should probably go to stderr.

Resources:

• https://logging.apache.org/log4j/1.x/apidocs/org/apache/log4j/PatternLayout.html
• https://github.com/iterate-ch/cyberduck/blob/master/defaults/src/main/resources/debug/log4j.xml
• https://stackoverflow.com/questions/7745885/log4j-logging-hierarchy-order