Administering Load Balancer
This section focuses on administering production environments and realistic test environments.
Subtopics
Enabling advisors to manage load balancing
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.Configuring high availability
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 failed.Using NAT forwarding to forward traffic
Using Network Address Translation (NAT) Dispatcher capability removes the limitation for the backend servers to be on a locally attached network. With the NAT forwarding method, Dispatcher load balances the incoming request to the server. The server returns the response to Dispatcher. The Dispatcher machine then returns the response to the client.Use encapsulation forwarding to forward traffic across network segments
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.Quiesce servers or services for maintenance windows
To remove a server or service from the Load Balancer configuration for any reason (updates, upgrades, service, etc.), you can use the dscontrol(or cbrcontrol) manager quiesce command. You cannot use quiesce in the Site Selector component.Restricting incoming traffic with ipchains and iptables
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.Logging with Load Balancer
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.Support for ICMP forwarding and messaging
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.Configure rules to manage traffic to busy or unavailable servers
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.Optimize connections with client-to-server affinity
Use the affinity feature to map a client IP address to a back-end server.Sample scripts to generate alerts and record server failure
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.


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