when and where the cookie will be reset when server restart

[gokusleepy2]

I want to migrate the session data from the cookies to the redis. I decode and get the session data from cookie, then I store it with the key of session_id at redis. But, when the server restart under the config of redis_session_store, the cookie is reset by a new session_id。I don't know when and where the cookie was reset. How to keep the resetting cookie with the same session_id?