Administering Load Balancer

This section focuses on administering production environments and realistic test environments.

Enabling advisors to manage load balancing
Tuning is a critical part of getting the best performance from your Web site, but tuning involves analyzing performance data and determining the optimal server configuration. This determination requires considerable knowledge about the various components in the application server and their performance characteristics. The performance advisors encapsulate this knowledge, analyze the performance data and provide configuration recommendations to improve the application server performance. Therefore, the performance advisors provide a starting point to the application server tuning process and help you without requiring that you become an expert.
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 has failed.
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 for server maintenance windows
To remove a server from the Load Balancer configuration for any reason (updates, upgrades, service, etc.), you can use the dscontrol manager quiesce command.
Optimize connections with client-to-server affinity
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.
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.
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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Last updated: September 10, 2012 09:00 AM EDT
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