gistfile1.rb

module MyNamespace
  class MyApp < Sinatra::Base
    ...

    after do
      $APP_LOG.info "do some logging here"
      ...
    end
    
    error do
      $APP_LOG.error "#{$!.message}: #{$@.join("\n")}"
      raise $! # yeah, yeah... I would do something else here, but this is just an example
    end

    ...
  end
end