Rails Semantic Logger replaces the Rails default logger with Semantic Logger, so that Rails, your application code, and many common gems all log through structured logging instead of plain text. When any large Rails application is deployed to production one of the first steps is to move to centralized logging, so that logs can be viewed and searched from a central location. That quickly falls apart when consuming human readable text logs: Log entries often span multiple lines (for example, stack traces), so unrelated lines end up interleaved in the centralized system. Complex regular expressions are needed to parse the text into machine readable fields for queries and alerts. Searches, alerts, and dashboards built on text are brittle: a small change to the logged text breaks them. Every log entry has a different format, making consistent searches difficult. Switching to structured logging, or logs in JSON format, makes centralized logging in testing and production far more powerful. Rails Semantic Logger also collapses the several lines Rails normally logs per request into a single structured "Completed" line, while keeping every field (controller, action, status, durations, and so on) searchable.
