A common logging format is desirable for a few reasons (list may not be complete):
- to apply an index schema and enable proper type coercion when logs are indexed in Elasticsearch (related incident)
- to simplify the log messages and make them easier to reason about and query for
- to speed up searches
- to simplify de-duplication efforts
- to simplify detection and removal of useless logs
- to make the upgrade to newer versions of Elasticsearch possible (Single-type mapping per index enforced -- 6.x | 7.x)