Add start_distribution to kernel environment

[josevalim]

Sometimes you may want to start Erlang without any
of its distribution services. This commit adds an
environment configuration that allows so.

Because the servers we don't start here are a subset
of the servers not started on minimal mode, we do
have a guarantee that the system can still operate
as the system operates without those apps on minimal
mode.

[josevalim]

@sirihansen now that OTP 22-rc.1 is out, do you have any thoughts on this PR? I would love to get this on OTP 22 because it would be essential to allow us to configure releases with Elixir itself. Thank you.

[sirihansen]

It would be really good to have some kind of test for this, to make sure we don't break it later on. Unless you have better ideas yourself, you could try either of

• test_server:start_node/3 with Type=peer. This starts a node which communicates back over a tcp connection without trying to connect via erlang distribution. The drawback in this case is that you cannot talk to it afterwards without setting up an own communication way - i mean, to verify that it worked (which children exist under kernel_sup, maybe).
• os:cmd/1 and print what you want to verify to stdout (which is then returned by os:cmd/1).

[josevalim]

• os:cmd/1 and print what you want to verify to stdout (which is then returned by os:cmd/1)

I assume something like done here?

otp/erts/emulator/test/distribution_SUITE.erl

Lines 824 to 827 in a94b54d

	Str = os:cmd(ct:get_progname()
	++ " -noshell -pa "
	++ proplists:get_value(data_dir, Config)
	++ " -s run"),

Thanks @sirihansen!

[josevalim]

@sirihansen pushed a test with os:cmd.

[sirihansen]

Thanks! It'll run in tests over the weekend.

[sirihansen]

The test runs nicely, but I just realized that it is in the emulator test and not in kernel (which is the affected application). Would you mind moving it to kernel_config_SUITE instead? (and please remove the comment here: https://github.com/erlang/otp/blob/master/lib/kernel/test/kernel_config_SUITE.erl#L62).

[josevalim]

@sirihansen done.

[vans163]

If we are going this way would like to add a note about EPMD, which presents problems as its always started by erlang as a daemon if its not running. This leads to weird behavior in things like supervised containers, as EPMD is part of the process tree, and when the VM dies, the supervisor still keeps thinking the tree is alive.

[josevalim]

@vans163 you can pass -start_epmd false in such cases. Or explicitly start it before out of the tree. Is that not enough?

[vans163]

@josevalim its not because you also need to shim the EPMD implementation or you get an error when running a node with -start_epmd false, Protocol 'inet_tcp': register/listen error: econnrefused.