If you write the code within the `gen_server` guidelines, state migration is supported by `code_change`: http://www.erlang.org/doc/man/gen_server.html#Module:c

If you write the code within the `gen_server` guidelines, state migration is supported by `code_change`: http://www.erlang.org/doc/man/gen_server.html#Module:code_change-3 http://www.erlang.org/doc/man/gen_server.html#Module:code_ch... For example: http://stackoverflow.com/questions/1840717/achieving-code-swapping-in-erlangs-gen-server http://stackoverflow.com/questions/1840717/achieving-code-sw... BTW, You can even support downgrade. :)