Logging

Servus automatically logs every service call with its arguments, outcome, and duration. No instrumentation code needed in your services.

What gets logged

Every call produces two log lines — one when it starts, one when it finishes:

Successful call

INFO  Calling Treasury::TransferGold::Service with args: {:from_account=>1, :to_account=>2, :gold_dragons=>50}
INFO  Treasury::TransferGold::Service succeeded in 0.013s

Business failure

INFO  Calling Treasury::TransferGold::Service with args: {:from_account=>1, :to_account=>1, :gold_dragons=>50}
WARN  Treasury::TransferGold::Service failed in 0.008s with error: Cannot transfer to the same account

Validation error

ERROR Treasury::TransferGold::Service validation error: "fifty" is not of type integer

Guard failure

WARN  Treasury::TransferGold::Service guard failed: Account must not be frozen

Event emission

INFO  Event :gold_transferred emitted with payload: {:transferred=>50, :from_balance=>950, :to_balance=>550}

Uncaught exception

ERROR Treasury::TransferGold::Service uncaught exception: ActiveRecord::RecordNotFound - Couldn't find Account with 'id'=999

Log levels

Outcome	Level	When
Call started	info	Every call, with arguments
Success	info	Call completed successfully, with duration
Business failure	warn	failure(...) returned, with error and duration
Guard failure	warn	Guard threw :guard_failure, with error message
Event emission	info	Event emitted via emits DSL, with payload
Validation error	error	Schema validation failed (arguments or result)
Uncaught exception	error	Exception raised and not handled by rescue_from

Logger configuration

Servus uses Rails.logger when available, otherwise Logger.new($stdout). Control the log level through Rails configuration:

# config/environments/production.rb
config.log_level = :warn  # Hides info-level call and success logs

Custom logging inside services

The automatic logging covers the lifecycle — call, outcome, duration. If you need to log something specific inside your call method, use Rails.logger (or whatever logger your app uses) as you normally would. Servus doesn't replace or wrap your application's logger.

def call
  Rails.logger.info("Transferring #{@gold_dragons} gold dragons from #{from_account.id} to #{to_account.id}")

  from_account.withdraw!(@gold_dragons)
  to_account.deposit!(@gold_dragons)

  success(transferred: @gold_dragons, from_balance: from_account.balance, to_balance: to_account.balance)
end

Sensitive data

Arguments are logged at info level. In production, either:

1. Set the log level to :warn to suppress argument logging entirely
2. Use Rails parameter filtering: config.filter_parameters += [:password, :ssn]
3. Pass IDs instead of full objects: Service.call(user_id: 1) not Service.call(user: user_object)