This section focuses on administering production environments and realistic test environments.
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.
The high availability feature involves the use of a second Dispatcher machine. The first Dispatcher machine performs load balancing for all the client traffic as it does in a single Dispatcher configuration. The second Dispatcher machine monitors the "health" of the first, and takes over the task of load balancing if it detects that the first Dispatcher machine has failed.
Use encapsulation forwarding when the back-end server is not located on the same network segment or if you are using virtualization technology and need to forward packets that are otherwise unable to be forwarded.
To remove a server or service from the Load Balancer configuration for any reason (updates, upgrades, service, etc.), you can use the dscontrol manager quiesce command.
The Load Balancer affinity feature maps a client IP address to a back-end server. Affinity is established once a packet's destination IP address matches the cluster, the destination port matches the Load Balancer port, and the source IP address matches.
Built into the Linux kernel is a firewall facility called ipchains. When Load Balancer and ipchains run concurrently, Load Balancer sees packets first, followed by ipchains. This allows the use of ipchains to harden a Linux Load Balancer machine, which could be, for example, a Load Balancer machine that is used to load balance firewalls.
Load Balancer posts entries to a server log, a manager log, a metric monitor log (logging communications with Metric Server agents), and a log for each advisor you use.
Load Balancer now supports forwarding and processing ICMP messages to improve the robustness of connection protocols and permit Load Balancer to receive ICMP fragmentation messages.
Use rules-based load balancing to fine tune when and why packets are sent to which servers. Load Balancer reviews any rules you add from first priority to last priority, stopping on the first rule that it finds to be true, then load balancing the traffic between any servers associated with the rule. It already balances the load based on the destination and port, but using rules expands your ability to distribute connections.
Load Balancer provides user exits that trigger scripts that you can customize. You can create the scripts to perform automated actions, such as alerting an Administrator when servers are marked down by the manager or simply record the event of the failure.