Working config for synchronous stream replication with both nodes on same host

== Hot standby ==

/etc/postgresql/10/main2/pg_hba.conf
host    replication     all             ::1/128                 md5
host    replication     all             127.0.0.1/32            md5
host    replication     repuser         ::1/0                   md5
host    replication     repuser         0.0.0.1/0               md5
local   replication     repuser                                 peer

/etc/postgresql/10/main2/postgresql.conf
wal_level = replica
#synchronous_commit = on
max_replication_slots = 12
synchronous_standby_names = 'main'
hot_standby = on
log_min_messages = warning
log_connections = on
log_statement = 'ddl'
log_replication_commands = on
lc_messages = 'C.UTF-8'

/etc/postgresql/10/main2/recovery.conf
standby_mode = 'on'
primary_conninfo = 'application_name=main2 host=localhost user=repuser port=5432 password=<plain text>'

== master ==
/etc/postgresql/10/main/pg_hba.conf
host    replication     all             ::1/128                 md5
host    replication     all             127.0.0.1/32            md5
host    replication     repuser         ::1/0                   md5
host    replication     repuser         0.0.0.1/0               md5
local   replication     repuser                                 peer

/etc/postgresql/10/main/postgresql.conf
wal_level = replica
#synchronous_commit = on
archive_mode = off
max_wal_senders = 12
max_replication_slots = 12
synchronous_standby_names = 'main2'
hot_standby = on
wal_receiver_timeout = 60s
log_min_messages = warning
log_connections = on
log_statement = 'ddl'
log_replication_commands = on
lc_messages = 'C.UTF-8'

/etc/postgresql/10/main/recovery.conf
standby_mode = 'off'
primary_conninfo = 'application_name=main host=localhost user=repuser port=5433 password=<plain text>'