Advisors are software agents that work within Load Balancer to
provide information about the load on a given server. A different advisor
exists for each standard protocol (HTTP, SSL, and others). Periodically, the
Load Balancer base code performs an advisor cycle, during which it individually
evaluates the status of all servers in its configuration.
Before you begin
Advisors are agents within Load Balancer. Their purpose is to assess
the health and loading of server machines. They do this with a proactive client-like
exchange with the servers. Advisors can be considered as lightweight clients
of the application servers.
By writing your own advisors for the Load
Balancer, you can customize how your server machines’ load is determined.
For
more information on how advisors work, read Advisors.
When using IPv6 protocols: If you are using IPv6 protocol
on your machine and want to use advisors, you must modify the protocol file.
To enable IPv6, insert the following line in the protocol file:
ipv6-icmp 58 IPv6-ICMP # IPv6 interface control message protocol
The protocol file is in the following directory:
The product provides several protocol-specific advisors for the
most popular protocols. However, it does not make sense to use all of the
provided advisors with Load Balancer. Load Balancer also supports the concept
of a “custom advisor” that allows users to write their own advisors.
Limitation
on using advisors with bind-specific server applications:
- In order to use advisors on bind specific servers, start two instances
of the server: One instance to bind on the cluster@port and
the other instance to bind on the server@port.
To determine if the server is bind specific, issue the netstat
-an command and look for the server@port.
If the server is not bind specific, the result from this command will be 0.0.0.0:80.
If the server is bind specific, you will see an address such as 192.168.15.103:80.
If using arp publish instead of
the ifconfig alias command, Load Balancer will support
the use of advisors when load-balancing servers with bind-specific server
applications when they are binding to the cluster IP address.
About this task
You can start an advisor for a particular port across all clusters
(group advisor). Or, you can choose to run different advisors on the same
port, but on different clusters (cluster specific advisor).
Note: If Load
Balancer is running on a computer with multiple network adapter cards, you
cannot force the source IP address of the packet to a specific address when
you want the advisor traffic to flow over a particular adapter.