Chapter 4. Configuration and customization 151
3. Create a junction from WebSEAL server 2 to each back-end server and
specify the UUIDs identified in Step 2. Use create –s –u and add –u.
Handling an unavailable stateful server
You can use the use-new-stateful-on-error stanza entry in the [junction]
stanza of the WebSEAL configuration file to control how WebSEAL responds to a
stateful server that becomes unavailable.
When use-new-stateful-on-error is set to yes and the original server becomes
unavailable during a session, WebSEAL directs the user’s next request to a
new replica server on the same stateful junction. If a new replica server is
found on that stateful junction, and is responsive to the request, WebSEAL
sets a new stateful cookie on the user’s browser. Subsequent requests during
this same session are directed to this same new server.
When use-new-stateful-on-error is set to no (the default, to keep compatibility
with previous versions) and the original server becomes unavailable during a
session, WebSEAL does not direct the user’s subsequent requests to a new
replica server on the same stateful junction. Instead, WebSEAL returns an
error and attempts to access the same server for subsequent requests by the
user during this session.
4.8.4 Junction throttling
High demand WebSEAL environments usually rely on server clusters made up of
multiple machines hosting replicated content and applications. A replica server
environment allows you to take individual servers offline to perform regular
maintenance. The network load is redistributed across the remaining replicas,
allowing the user experience to proceed without disruption.
Junction throttling allows you to gradually take a junctioned back-end Web server
offline without interrupting the transactions of users with existing sessions. The
throttling action on a junction is particularly useful for allowing stateful sessions,
such as shopping cart transactions, to continue until completed.
Junction throttling accomplishes the following actions:
The throttled server continues to process current and subsequent requests
from users with sessions created before the throttle action was taken.
The throttled server blocks all requests from unauthenticated users and new
authenticated users and directs these requests to other available replica
servers on the same junction.
As the current users finish their sessions, the throttled server eventually
becomes idle and can be taken offline.