Distributed application problem

[Paul Oliver]

Hi all,

I'm having a problem with a distributed application where my app ends
up running on two nodes.  I've set up a test application using
http://www.erlang.org/doc/design_principles/distributed_applications.html
as a guide.  The app is a simple dummy app that does nothing but
start.  The config files are as described in §9.2:

puzza@REDACTED:~/src/distr_test$ cat config/distr_test_cp[123].config
%%-*-erlang-*-
[
 {kernel,
  [{distributed, [{distr_test, 5000, [cp1@REDACTED, {cp2@REDACTED,
cp3@REDACTED}]}]},
   {sync_nodes_mandatory, [cp2@REDACTED, cp2@REDACTED]},
%   {sync_nodes_optional, [cp2@REDACTED, cp2@REDACTED]},
   {sync_nodes_timeout, 5000}
  ]
 }

].
%%-*-erlang-*-
[
 {kernel,
  [{distributed, [{distr_test, 5000, [cp1@REDACTED, {cp2@REDACTED,
cp3@REDACTED}]}]},
   {sync_nodes_mandatory, [cp1@REDACTED, cp3@REDACTED]},
%   {sync_nodes_optional, [cp1@REDACTED, cp3@REDACTED]},
   {sync_nodes_timeout, 5000}
  ]
 }

].
%%-*-erlang-*-
[
 {kernel,
  [{distributed, [{distr_test, 5000, [cp1@REDACTED, {cp2@REDACTED,
cp3@REDACTED}]}]},
   {sync_nodes_mandatory, [cp1@REDACTED, cp2@REDACTED]},
%   {sync_nodes_optional, [cp1@REDACTED, cp2@REDACTED]},
   {sync_nodes_timeout, 5000}
  ]
 }

].

I'm starting the three nodes using:

erl -sname cp1 -config config/distr_test_cp1 -pa ebin/
erl -sname cp2 -config config/distr_test_cp2 -pa ebin/
erl -sname cp3 -config config/distr_test_cp3 -pa ebin/

Then starting the app separately on all three nodes with
application:start(distr_test).  Now when I stop cp1 and cp2 the
application is transferred to cp3 as expected.  However, when I
restart cp1 and cp2 along with the application, I find that it's
running on both cp1 and cp3:

(cp1@REDACTED)2> application:which_applications().
[{distr_test,"Distribution Test","0.1"},
 {stdlib,"ERTS  CXC 138 10","1.17.1"},
 {kernel,"ERTS  CXC 138 10","2.14.1"}]
(cp1@REDACTED)3>

(cp2@REDACTED)2> application:which_applications().
[{stdlib,"ERTS  CXC 138 10","1.17.1"},
 {kernel,"ERTS  CXC 138 10","2.14.1"}]
(cp2@REDACTED)3>

(cp3@REDACTED)2> application:which_applications().
[{distr_test,"Distribution Test","0.1"},
 {stdlib,"ERTS  CXC 138 10","1.17.1"},
 {kernel,"ERTS  CXC 138 10","2.14.1"}]
(cp3@REDACTED)3>

I note that when I run start on cp1 it's a normal start rather than a
takeover.  Can anybody tell me what I'm doing wrong?

Regards,
Paul.