Plain Ruby on Rack, no framework. How do its logs land on Laravel Cloud?

Writes at a given severity to STDOUT. Levels below LOG_LEVEL are dropped. The block form is only evaluated if the level is enabled. The app's formatter adds the request id.

LOGGER = Logger.new($stdout, level: :info)
LOGGER.info "message"
LOGGER.debug { expensive_string }

The closest thing stdlib Logger has to tags: a progname per logger instance, printed on every line.

billing = Logger.new($stdout, progname: "billing")
billing.info "message"

The most used structured logging gem outside Rails. Supports named loggers, payload hashes, tags and timing blocks. It writes from a background thread by default. Set LOG_FORMAT=json for JSON output.

logger = SemanticLogger["Checkout"]
SemanticLogger.tagged("billing") do
  logger.info("Charged card", user_id: 42)
  logger.measure_info("Called API") { ... }
end

One Apache-style line per request. Rack writes it to rack.errors by default, which Puma points at STDERR. Change it with ACCESS_LOG=stdout|off. Pick a status to see how the platform treats it.

use Rack::CommonLogger
# 1.2.3.4 - - [12/Oct/2026:02:23:12 +0000] "GET /status?code=503 HTTP/1.1" 503 - 0.0004

Every Rack server gives the app an error stream in env["rack.errors"]. Puma connects it to STDERR, and frameworks often write warnings to it.

env["rack.errors"].puts "message"

Passing an exception object to the logger. Stdlib prints the message, class and backtrace as one multi-line entry. SemanticLogger records it as a structured exception.

rescue => e
  LOGGER.error(e)
  SemanticLogger["Demo"].error("Caught an error", e)

With no framework, Puma catches the error and writes a one-line summary to STDERR. In production there's no backtrace. It returns a bare 500, so use the browser back button to return.

raise RuntimeError, "boom"

Logs from a thread after the response has gone, so there's no request id. This is how plain Ruby apps usually do background work.

Thread.new { LOGGER.info "message" }

Writes straight to the process streams. Checks whether the platform captures both, and whether it treats stderr as errors.

$stdout.puts "message"
$stderr.puts "message"
warn "message"