Ok. Thank-you for pointing this. I have just tried it, and this work great even for nodes that are not properly power off (plug removed).
Ok. For the first check, I was using
bdr.bdr_test_remote_connectback(peer_dsn, local_dsn), getting the dsn from the bdr.bdr_nodes table; but using the
pg_stat_replication table is problably quicker and simpler.
Thank-you again,
Sylvain