Disabling And Enabling Real Servers; Health Checks For Real Servers - Radware Alteon Application Manual

Alteon Application Switch Operating System Application Guide
Server Load Balancing

Disabling and Enabling Real Servers

If you need to reboot a server, ensure that new sessions are not sent to the real server and that
current sessions are not discarded before shutting down the server, using one of the following
methods:
• Use the following command with the n (none) option to suspend connection assignments to the
real server:
>> # /oper/slb/dis <real server number> n
When the current session count on your server falls to zero, you can shut down your server.
• If you have configured persistence on the real server, use the following command with the p
(persistent) option to suspend connection assignments (except for persistent http 1.0 sessions)
to the real server:
>> # /oper/slb/dis <real server number> p
When the current session count on your server falls to zero and when persistent sessions for the
real server have aged out (refer to the persistence parameters you have set for this real server),
you can shut down your server. For more information, see
• When maintenance is complete, use the following command to enable the real server:
>> # /oper/slb/ena <real server number>
Alteon resumes assignment of connections to this real server immediately.
Table 21 compares the behavior of the
commands:
Behavior
Clearing all old sessions
immediately after executing
command
Allowing persistent HTTP
1.0 sessions
The grace option is enabled only if the real server is in "failed" state and not in "disabled" state
(failed by health check). For example, consider HTTP service when the grace option is enabled. After
handling client requests for some time, the real server is marked failed by the health check, but the
remaining sessions to the real server are still kept to maintain previous connections from client to
the real server.

Health Checks for Real Servers

Determining the health for each real server is a basic function for SLB. By default, Alteon checks the
health of a real server using ICMP.
Once servers are attached to groups which, in turn, are attached to services, Alteon checks the
availability of the services running on the server using the health checks configured for the group.
However, it is possible to override this behavior and configure for each real server its own health
checks.
Alteon checks the availability of real servers using timers defined in the health check. However, it is
possible to override timers per real server. The following example illustrates how the health check
interval and the number of retries can be changed:
176
>> # /oper/slb/dis
Table 21: Disabling Commands Behavior
>> # /oper/slb/dis
No
Yes/No
Persistence, page 583.
and
>> # /cfg/slb/dis
>> # /cfg/slb/dis
Yes
N/A
Document ID: RDWR-ALOS-V2900_AG1302