[erlang-questions] Release upgrade of an app without a top supervisor

[Roberto Ostinelli]

If anyone else needs a solution for this, here is mine.
First, build your release upgrade package as you normally would. I use
rebar, so I issue:

$ rebar generate-appups previous_release=myapp-1.4.6

Modify your .appup files as needed, then generate the upgrade package:

$ rebar generate-upgrade previous_release=myapp-1.4.6

Then, open up the upgrade package, and look for the relup file
releases/1.5.0/relup.
In your relup instructions, before the point_of_no_return instruction
ensure to load the setup app:

{load_object_code,{setup,"1.5.0",[setup,setup_gen,setup_lib]}},

Just after the point_of_no_return, ensure to stop it:

{apply,{application,stop,[setup]}},

Finally, after all the other instructions ensure to start it:

{apply,{application,start,[setup,permanent]}}


Now, on a live system, check which applications are live:

1> application:which_applications().
[{myapp,"My App.","1.4.6"},
 {exometer_core,"Code instrumentation and metrics collection package.",
                "1.4.6"},
 {setup,"Generic setup application for Erlang-based systems","1.4.6"},


Then proceed to the normal upgrade:

2> release_handler:unpack_release("myapp_1.5.0").
3> release_handler:install_release("1.5.0").
4> release_handler:make_permanent("1.5.0").


Check applications again:

5> application:which_applications().
[{setup,"Generic setup application for Erlang-based systems","1.5.0"},
 {myapp,"My app.","1.5.0"},
 {exometer_core,"Code instrumentation and metrics collection package.",
                "1.5.0"},

You can see that it upgraded successfully.

Hope this can help somebody else.

Best,
r.
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