Alteon Application Switch Operating System Application Guide
Health Checking
Document ID: RDWR-ALOS-V2900_AG1302
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To enable the slow start mode of a real server in a group
Enter the following command:
DSR Health Checks
Direct Server Return (DSR) health checks are used to verify the existence of a server-provided
service where the server replies directly back to the client without responding through the virtual
server IP address. In this configuration, the server will be configured with a real server IP address
and virtual server IP address. The virtual server IP address is configured to be the same address as
the user's virtual server IP address. When DSR health checks are selected, the specified health
check is sent originating from one of Alteon's configured IP interfaces, and is destined to the virtual
server IP address with the MAC address that was acquired from the real server IP address's Address
Resolution Protocol (ARP) entry.
Alteon lets you perform health checks for DSR configurations. For more information, see
. Alteon can verify that the server correctly responds to requests made to
the virtual server IP address as required in DSR configurations. To perform this function, the real
server IP address is replaced with the virtual server IP address in the health check packets that are
forwarded to the real servers for health checking. With this feature enabled, the health check will fail
if the real server is not properly configured with the virtual server IP address.
Note:
The DSR VIP health check (cfg/slb/group/viphlth) is enabled by default. This has no
effect on the health check unless the real server is configured with DSR.
Advanced Group Health Check
Alteon lets you configure an expression to fine-tune the selected health check for a real server
group. For example, you have configured a real server group with four real servers. Two of the real
servers handle the contents of the Web site and the other two real servers handle audio files. If the
two content servers fail due to traffic distribution, then you want the two audio servers to fail.
However, you want the audio servers up if at least one of the content servers is up.
The advanced group health check feature lets you create a boolean expression to health check the
real server group based on the state of the virtual services. This feature supports two boolean
operators: AND and OR. The two boolean operators are used to manipulate TRUE/FALSE values as
follows:
•
OR operator (|)—A boolean operator that returns a value of TRUE if either or both of its
operands are TRUE. This is called an inclusive OR operator.
•
AND operator (&)—A boolean operator that returns a value of TRUE if both of its operands are
TRUE.
Using parenthesis with the boolean operators, you can create a boolean expression to state the
health of the server group. The following two boolean expressions show two examples with real
servers 1, 2, 3, and 4 in two different groups:
>> Main# /cfg/slb/group <group_number>/slowstr <value_in_seconds>
