Custom rules for distributing requests

Using custom settings to direct requests

NetCache default settings for distributing outbound requests are highly efficient, and most organizations do not require custom settings. However, custom rules can be created to direct requests to hierarchy members or to origin servers that are local or remote to the NetCache appliance you are configuring. For example, custom rules can be set to

Direct requests of a specific type to a specific hierarchy member
Specify a backup host for failover

You define custom rules by creating forwarding rules on the Hierarchies - Forwarding Rules page (Setup tab > Hierarchies > Forwarding Rules).

Note
Logical roles must be assigned before custom rules are created.

Custom settings disable default forwarding

If you create a rule to handle a protocol-specific request, default forwarding for all related protocols is disabled. This means that in addition to creating a rule to direct a protocol to a specific member of the hierarchy, you must also create a rule to manage the remainder of HTTP, FTP, FTP over HTTP, Gopher, and Tunnel requests and all other supported protocols to other members of the hierarchy.

Ordering rules

NetCache executes rules in the order in which they are listed. If you create custom rules for directing requests, consider whether you need to modify the order of those rules to ensure that specific rules are executed before general rules. For example, if you create a custom rule to designate a backup host or a backup cluster, order the rule lower in the rules list than a primary host rule or cluster rule. This way, the backup rule is executed only if the primary rule fails

In another example, assume that you want all HTTPS requests to be tunneled to a specific host. List the custom rule that directs tunnel requests to a specific host before the more general noncacheable rule.

Custom settings for directing requests

Custom rule settings can be used to forward requests of a specific type to a specific hierarchy member.

In the following example, custom settings on NetCache A forward all HTTP requests to NetCache B and forward all requests for streaming media to NetCache C. Custom rule settings for HTTP, MMS, and RTSP disable automatic distribution for all protocols. This means that NetCache A must also be configured with a custom rule that specifies forwarding for FTP, Tunnel, and Gopher requests.

Custom settings for specifying primary host backup

Custom rule settings can be used to specify a backup host to support continuous connectivity if a primary host fails.

In the following example, NetCache B identifies NetCache D as a primary parent, and NetCache C as a secondary parent. NetCache A identifies NetCache C as a primary parent, and NetCache D as a secondary parent. If C goes down, D provides backup for C and handles requests for A. If D goes down, C provides backup for D and handles requests for B.

Custom settings to support failover

Custom rule settings can be used to provide failover if a connection to the Internet fails.

Direct monitor is a NetCache hierarchy feature that can be set up to monitor Internet connectivity using direct connections. Monitoring direct connections enables NetCache to detect and route around connectivity problems. NetCache uses TCP to establish connections to hosts specified in the NetCache configuration. When connection attempts to all hosts fail, the Internet connection is considered down, and NetCache fails over to the next forwarding rule for directing requests.

If NetCache fails to connect to a destination specified in a hierarchy forwarding rule, the next user-defined rule is evaluated. If NetCache is unable to connect using any of the forwarding rules, NetCache bypasses the hierarchy and retrieves the content directly from the Internet (known as the "direct" distribution method). You can disable failover on a per-rule basis to control traffic that should not fail over and ultimately be forwarded directly to the Internet.

In the following example, NetCache A and NetCache B are set up to monitor direct connections to the Internet. Each member of the hierarchy provides failover if one member loses connectivity.

Custom settings to support services

Custom rule settings can be used to define conditions for handling requests of a specific type.

In the following example, the parent resolves requests for Word documents, and then sends the files to an ICAP server where the content is scanned for virus contamination before being returned to the client. The ICAP server is configured separately on the parent cache and is not part of the hierarchy.