Generates a .appup file for the given application, start version, and upgrade version.

The appup file generated by make/5 is much simpler than that by similar appup generation tools, as make/5 does not use update instruction (which is called "synchronized code replacement"). Synchronized code replacement (which uses code_change/3) is risky because

• It's difficult to get it right, difficult to test.
• Suspending target processes entails traversing the whole supervision tree. All processes in the tree must respond to system messages in a timely manner.
  • Processes governed by some libraries might not properly handle system messages; if it's the case all OTP applications will be restarted by :init.restart().
  • Some process might not respond in a timely fashion; resulting in brutal kill of the unresponsive process.
  • Suspending handling of non-system messages might cause performance issues.

Therefore we simply don't use OTP's code change mechanism; to change data format of process state we

• implement callbacks to check/convert the data format version, or
• avoid hot code upgrade and replace the working instances with new ones.

On the other hand, make/5 automatically resolves interdependencies between changed modules (which other tools don't).

Parameters for make/5

• name : the application name as an atom
• v1 : the start version, such as "0.0.1"
• v2 : the upgrade version, such as "0.0.2"
• v1_dir: the path to the v1 artifacts (rel/<app>/lib/<app>-0.0.1)
• v2_dir: the path to the v2 artifacts (_build/prod/lib/<app>)