3.  Master/slave replication

     INN supports a simple model of replicated news databases:  a single
master  host  pushes  out updates to its slaves.  The master is the only
host that receives articles -- this includes both outside newsfeeds  and
articles  written by local users.  The slaves only receive articles from
the master.

     No special work is required to set up a master host.

     A slave is set up by starting innd with the "-S" flag to  specify
the  name  or  IP  address  of  the master host.  This should be done by
modifying the "FLAG" variable in your _PATH_NEWSBOOT script.  If  innd
is  started  with  the  "-S"  flag it will pass this flag on to nnrpd.
This means that when anyone connects to the slave and  does  a  "POST"
command, nnrpd will connect to the master and offer the article.

     You must make sure that the slave's entry in the master's newsfeeds
file  sends  all  articles (e.g., don't have any exclusions).  Since the
nnrpd on the slave host will usually add its name to  the  Path  header,
you  should  add  "Ap"  to the flags field of the slave's entry on the
master.

     Once the slave has been set up it is necessary to have  the  master
feed it.  This is done by using an extension to the NNTP protocol.  This
extension, the "XREPLIC" command, is documented in innd.8.   In  order
to  do  this  you  will  have to set up a newsfeeds entry for the slave.
This should be a standard entry except that you will need to  have  both
the  filename and the replication information written int the batchfile.
To do this, put "WnR" in the flags field of the entry.

     When you want to actually send the articles to the slave  site  you
will  have  to specify the "-S" flag in your innxmit command.  Current
versions of nntplink use the "-x" flag.

     When running as a  slave,  innd  is  very  paranoid  about  staying
synchronized  with  its  master.   Most noticeably, you should make sure
that all newgroup and rmgroup control messages are  handled  identically
on both systems.

     Finally, note that postings made  on  the  slave  (via  nnrpd)  are
actualy  sent to the innd on the master, so the slave must be treated as
a sending host, not a newsreading host.