Rack middleware that makes sure requests don't get a dead Sequel connection

sequel_reconnector.rb

class SequelReconnector
  RETRY_LIMIT = 10 # Match this to your connection pool size.
  
  def initialize(app, db)
    @app = app
    @db  = db
  end
  
  def call(env)
    retries   = 0
    connected = false
    
    begin
      @db.synchronize do
        @db.run(@db.select(1).sql)
        connected = true
        @app.call(env)
      end
    rescue Sequel::DatabaseDisconnectError
      if connected || retries > RETRY_LIMIT
        raise
      else
        if retries > 0
          @db.loggers.each do |logger|
            logger.warn("SequelReconnector: Retrying connection...")
          end
        end
        
        retries += 1
        
        retry
      end
    end
  end
end