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To Upgrade Components Without Loss of Service
In a clustered environment, a rolling upgrade redeploys an application with a
minimal loss of service and sessions. A session is any artifact, that can
be replicated, for example:
HttpSession
SingleSignOn
ServletTimer
DialogFragment
Stateful session bean
You can use the load balancer and multiple clusters to upgrade components
in GlassFish Server without any loss of service. A component can be,
for example, a JVM machine, the GlassFish Server software, or a web application.
A rolling upgrade can take place under light to moderate loads. The
procedure requires about 10-15 minutes for each GlassFish Server instance.
Applications must be compatible across the upgrade. They must work correctly during
the transition when some instances are running the old version and other instances
are running the new version. The old version and the new version
must have the same shape of serializable classes that form object graphs that
are stored in sessions (for example, nontransient instance variables) . If the
shape of these classes must change, the application developer must ensure that correct
serialization behavior occurs. If the application is not compatible across the upgrade,
the cluster must be stopped for a full redeployment.
This approach is not possible if the application upgrade involves a change
to the application database schema.
Caution - To prevent the risk of version mismatch when a session fails over,
upgrade all instances in a cluster at the same time. Otherwise a
session might fail over to an instance where different versions of components are
running.
Perform this task on each cluster separately. A cluster acts as a
safe boundary for session failover for instances in the cluster. Sessions in
one cluster can never fail over to sessions in another cluster. Therefore, the
risk of version mismatch is avoided.
- Stop the cluster.
- Upgrade the component in that cluster.
- Start the cluster.
See Also
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To Enable or Disable an Application That Is Deployed to a Cluster
To Enable or Disable Load Balancing for an Application That Is Deployed to a Cluster
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