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Administration Tip: Increasing
NNTP Reliability Using a
Master/Subordinate
Arrangement
Posted: October 02, 2001
Because Exchange 2000 clustering
does not support Network News Transfer Protocol
(NNTP) components, consider using a master/subordinate
(previously known as
master/slave) arrangement to increase NNTP reliability.
A master/subordinate
arrangement involves keeping newsgroup information
on more than one server. Keeping
newsgroup information on more than one server
reduces the impact in situations where a
server becomes unavailable. One possible configuration
would be to use one master
server and one or more subordinate servers. With
such a configuration, you can configure
your newsgroup DNS in two ways:
Configure DNS so that users access newsgroups
through a specific subordinate
server.
Configure DNS using round robin DNS so that users
access newsgroups through
any available subordinate server. Configuring
round robin DNS offers additional
reliability because users can continue to use
all newsgroup functionality even if one of
the subordinate servers becomes unavailable.
Note: When you
set up your NNTP master/subordinate arrangement,
configure a feed
from each subordinate server to the master server.
Do not configure any feeds between
subordinate servers.
For example, Contoso, Ltd., a fictitious company
that previously used only one server to
store newsgroup information, decides to use a
master/subordinate arrangement to
increase reliability. Contoso configures its master
news server
(mynewsserver.contoso.com) to point to three subordinate
news servers
(subordinate1.contoso.com, subordinate2.contoso.com,
and subordinate3.contoso.com).
Contoso also configures round robin DNS so that
users will gain access to newsgroups
through either subordinate1, subordinate2, or
subordinate 3. With this configuration,
when a Contoso user connects to the newsgroups
from his or her browser, he or she is
routed to one of the subordinate servers (for
example, subordinate1). When the user posts
a message to subordinate1, the message replicates
to the master server, and then the
master server replicates the message to subordinate2
and subordinate3. That new message
post is not available to any users (that is, the
message cannot be seen by any of Contoso's
users), until it successfully replicates to the
master server. After the replication occurs,each
subordinate server contains the same content.
Master Server or Subordinate Server Failure
If the master server becomes unavailable, users
can still view the messages within the
newsgroups. They can even create and submit new
posts. However, any new posts
created on any subordinate server while the master
server is unavailable will not be
available to any users. The new posts are not
available because the master server has not
replicated them to the subordinate servers. Each
subordinate server holds any pending
posts until the master server is available. After
the master is available, it accepts any
pending posts, and then replicates those messages
to the subordinate servers. After
replication occurs, each subordinate server contains
the same up-to-date content. In this
scenario, the only temporary interruption of service
to users is that newly posted
messages cannot be viewed.
If one of your subordinate servers becomes unavailable,
and if you configured your
NNTP to use round robin DNS, your users have full
newsgroup functionality because
they can connect to another available subordinate
server. In this scenario, remove the IP
address of the unavailable subordinate server
from your round robin DNS configuration.
After you remove the IP address of the unavailable
subordinate server from DNS, users
who connect to the newsgroups will be pointed
to one of the available subordinate
servers. If you do not remove the IP address of
the unavailable subordinate server, users
will continue to be routed to the unavailable
subordinate server. If any of your users were
connected to the subordinate server when it became
unavailable, they must restart their
browsers to continue using the newsgroups because
they may have cached information
specifying the now unavailable subordinate server.
When the subordinate server becomes
available again, you must reconfigure the NNTP
round robin DNS to include the IP
address of the subordinate server.
If one of your subordinate servers becomes unavailable
and your NNTP does not use
round robin DNS, your users who gain access to
newsgroups through that unavailable
subordinate server will lose all NNTP functionality.
In this scenario, you must change
your configuration so that users who access newsgroup
information on the unavailable
subordinate server can access newsgroups through
one of your other subordinate servers.
After the subordinate server is once again available,
reconfigure your NNTP access to the
subordinate server so that users can access newsgroups
through their original subordinate
server.
Master Server and Subordinate Server Newsgroup
Hierarchy
Considerations
When you use a master/subordinate arrangement,
keep in mind the following
considerations:
When creating newsgroup hierarchies, only newsgroups
that are created using
control messages will be automatically created
on the subordinate servers. For more information
about using control messages, see the Exchange
online documentation.
Newsgroups created by using System Manager or
by using the Rgroup.vbs
command at a command prompt do not replicate to
other subordinate servers until a
message is posted to the group on the master server.
For more information about
using Rgroup.vbs, see the Exchange online documentation.
Users cannot post messages on a subordinate server
until the newsgroup to which
they want to post has been replicated to that
subordinate server.
After you establish your newsgroup hierarchy,
you should replicate it to the subordinate
servers by doing one of the following:
Post a test message in the group
on the master server,
Create an identical hierarchy on each subordinate
server, or
Create your newsgroups using control messages.
For more information about NNTP
master/subordinate arrangements, see the
Exchange 2000 online documentation.
This tip is provided by the Microsoft
Exchange User Education team.
For additional information, see the Microsoft
TechNet Exchange site.
