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 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 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 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.