4. Upgrade when Erlang/OTP has Changed
4 Upgrade when Erlang/OTP has Changed
4.1 Introduction
As of Erlang/OTP 17, most applications deliver a valid application upgrade file (appup). In earlier releases, a majority of the applications in Erlang/OTP did not support upgrade. Many of the applications use the restart_application instruction. These are applications for which it is not crucial to support real soft upgrade, for example, tools and library applications. The restart_application instruction ensures that all modules in the application are reloaded and thereby running the new code.
4.2 Upgrade of Core Applications
The core applications ERTS, Kernel, STDLIB, and SASL never allow real soft upgrade, but require the Erlang emulator to be restarted. This is indicated to the release_handler by the upgrade instruction
