Chapter 5. Intelligent Management 129
5.6.3 Concepts
The application edition management feature provides the following capabilities:
Rollout indicates policies that allow you to switch from one edition to another edition with
no loss of service.
Concurrent activation where multiple editions can be concurrently active for an extended
period.
A
validation mode to send selective traffic to verify the correct operation.
Rollout
Rollout activation activates one edition in place of another, ensuring an interruption-free
update in the process. Thus, all application requests are serviced during the rollout and none
are lost. This process ensures continuous application operation from the perspective of the
customers of that application. To do this, the application edition manager carefully
coordinates the activation of the edition and the routing of requests to the application.
During rollout, you make the following choices:
Soft or hard rollout
A soft rollout stops and starts only the application, whereas a hard rollout stops and starts
the application server. You might consider a hard rollout if an application must reload
native code.
Atomic or group rollout
An atomic rollout guarantees that two editions do not service requests at the same time,
whereas a group rollout does not make this guarantee. The atomic rollout can queue
requests briefly in the on-demand router to guarantee atomicity. A group rollout does not
queue requests.
Drainage interval
The drainage interval is the
maximum amount of time that the application edition manager
waits for sessions to expire before stopping an application server. During this interval, no
new sessions are established on the application server, but requests with affinity continue
to be routed to the application server. If all sessions expire before the completion of the
drainage interval, the application server is stopped and the rollout continues. Therefore,
this interval is the maximum time to wait, but the actual time might be much shorter,
depending on the active session count.
Replacement of one edition with another in a production environment requires certain
discipline in the evolution of the application. Because edition replacement happens while
application users are potentially accessing the previous application edition, the new edition
needs to be compatible with earlier versions. Thus, the new edition cannot add or change any
existing application interfaces, including essential behavior. New interfaces can be added. In
addition, existing interfaces can be algorithmically corrected and, in some cases, even
extended and remain compatible with existing application users.
130 WebSphere Application Server V8.5 Concepts, Planning, and Design Guide
Figure 5-6 shows an example of a group rollout scenario. In the diagram, a dynamic cluster is
created that consists of three servers. You first need to divide the cluster into groups, which
tells the application edition manager how many servers to update at the same time.
Performing a rollout to a group results in the servers in each group being upgraded to the new
edition at the same time. Each server in the group is quiesced, stopped, and reset.
Figure 5-6 Rollout policies
As the rollout is run in Figure 5-6, one server in the cluster is moved from Edition 1.0 to
Edition 2.0. During this time, the server does not receive user requests that are directed from
the on-demand router, and the server is stopped. All application requests are sent to the
servers that are running Edition 1.0. After the server that is running Edition 2.0 is available,
application requests are directed by the on-demand router to that server. Any servers that are
still running Edition 1.0 do not serve requests until the edition is updated to Edition 2.0.
Concurrent activation
Concurrent activation enables you to activate the same edition on different servers or
clusters. To use multiple editions concurrently, you must distinguish user requests from one
another so that the requests are sent to the application server that hosts the appropriate
edition. For example, if you introduce a new edition of an application, you might want only a
select group of users to test the edition.
When multiple editions of the same application are concurrently available to users, the
on-demand router needs information to differentiate between the active editions. Based on
that information, it then intelligently routes the request to the intended edition. You must
configure a routing policy that tells the on-demand router to which edition to route a request.
The routing policy is stored as part of the application metadata.

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