Brocade Virtual ADX Server Load Balancing Guide (Supporting ADX v03.1.00) - Manual (Page 232)

216 Brocade Virtual ADX Server Load Balancing Guide
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Boolean health checks
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Boolean health checks
Boolean health-check policies
You can configure a group of Layer 4 and Layer 7 health checks as a health-check policy and
associate the group with a specific application port on a real server.
1
Health-check policies enable
you to assess the health of any application port using the health-check mechanisms for ports
well-known to the Brocade Virtual ADX. In addition, health-check policies let you use multiple
checks with different parameters and base a port’s health on successful completion of all or any
one of the individual checks in the policy.
Depending on the conditions you specify when you configure a health-check policy, the Brocade
Virtual ADX will bring the application port on a server down in one of the following cases:
• Any one of the servers fails its health check (individual health checks combined using AND
condition) – In this case, all servers in the policy must pass their health checks. Otherwise, the
Brocade Virtual ADX considers all of the servers to have failed the health checks and brings
down the application on all servers that are checked by the policy.
• All of the servers fail their health checks (individual health checks combined using OR
condition) – In this case, an application port remains up as long as at least one of the servers
checked by the policy passes its health check.
For finer control, you can combine OR and AND conditions.
Health-check policy
Health-check policies consist of element-action expressions and logical expressions.
• An Element-action expression consists of the IP address of the server, the Layer 4 protocol
(TCP or UDP), and the application port on the server. For some applications, the element-action
expression can also include Layer 7 application-specific health check information.
• A Logical expression is a set of element-action expressions joined by the Boolean operators
OR, AND or NOT.
- To create a health-check policy that is successful if at least one of the applications passes
its health check, use OR.
- To configure a health-check policy that is successful only if the Brocade Virtual ADX
receives a successful reply from all servers and application ports in the policy, use the
operator AND.
- To configure a health-check policy that is successful if none of the elements responds to
the health check, use the operator NOT.
You can use the same element-action expressions in multiple logical expressions if desired. You
can configure up to 254 health-check policies.
1. Real servers include those added using the server real-name command and those added using
the server remote-name command. Generally, both types of servers are referred to as real
servers. An application port is a port that uses the TCP or UDP protocol. You associate
health-check policies with TCP or UDP ports on the real servers (not with physical ports on the
servers).