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Nirvana servers can be clustered
together to form part of a single logical server. This
can then be used to achieve HA (High Availability) etc.
For example if you want to set up a cluster running
across two different machines with Realm1 running
on host1.my-Channels.com and Realm2 running
on host2.my-Channels.com.
Firstly, you create a cluster with Realm1 and Realm2.
Then you create cluster channels and queues which ensures
these objects exist in both servers.
For information on how to achieve this, please review
the Nirvana Administration
Tool guide.
The next step is to setup your clients so that they
are configured to swap between Realm1 and Realm2 in
case of failures.
When you initialise a client session
with a Nirvana server you provide an array of RNAME
urls as the argument to the nSessionAttributes object.
This ensures that if you lose the connection to a particular
Nirvana Realm, the session will be automatically reconnected
to the next realm in the RNAME array.
Using the configuration above where cluster channels
exists on each Realm, disconnected clients will automatically
continue publishing/subscribing to the channel on the
newly connected realm.
For example, to use the two Realms described above
for failover you would use the following as your RNAME
value using a comma separated list of individual RNAMES
RNAME=nhp://host1.my-Channels.com:80,nsp://host2.my-Channels.com:9000
If all subscribers and publishers are configured in
this way then failover is provided in each of the following
scenarios.
scenario: subscriber loses connection to
a Realm
if a subscriber is consuming data from the sales channel
on Realm1 and loses its connection it will automatically
attempt to connect to its additional RNAMES (in this
case nsp://host2.yourdomain:9000) and resume consuming
from where it left off.
scenario: publisher loses connection to a
Realm
If a publisher loses a connection to its Realm it will
automatically reconnect to the alternative realm and
continiue publishing there. For more information on
HA configuration options please contact the my-Channels
support team who will be happy to outline the pros
and cons of the various HA configurations available.
scenario: publisher and subscriber are connected
to different realms.
As channels on Realm1 and Realm2 are cluster channels
events published to a sales channels on either Realm
will be passed to sales channel on the other realm.
As long as subscribers are consuming from a sales channel
on one of the realms they will receive all events. Thus
full guaranteed delivery is provided even if the publisher
is publishing to Realm1 and subscribers are consuming
from Realm2.
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