Outputting useful logs is a key part of building an observable service. What constitutes a useful log is subjective, but a good set of guidelines is that logs should contain timestamped information about key events in a system. A good logging system supports the notion of configurable log levels, so the amount of information sent to logs can be dialed up or down for a specific amount of time depending on the needs of engineers working with the system. For example, when testing a service against failure scenarios in production, it may be useful to turn up the log level and get more detail about events in the system.
The two most popular logging libraries for Java applications are Log4j (https://logging.apache.org/log4j/2.x/) and Logback (https://logback.qos.ch/). By default, both of these libraries will emit log entries in an unstructured format, usually...
