The ProxySG offers multiple configuration options that allow you to treat cached objects in a way that best suits your business model.
The following table lists the options that you can configure.
Table 8–2 Settings for Configuring the Object Caching Policy
Note: This feature is only available through the CLI.
Settings to Configure Object Caching Notes
Setting the maximum object cache size Determines the maximum object size to store in the ProxySG. All objects retrieved that are greater than the maximum size are delivered to the client but are not stored in the ProxySG. Default: 1024 MB
Section B: Configuring the HTTP Proxy Performance
Setting the TTL for negative responses in cache
Determines the number of minutes the SGOS stores negative responses for requests that could not be served to the client.
The OCS might send a client error code (4xx response) or a server error code (5xx response) as a response to some requests. If you configure the ProxySG to cache negative responses for a specified number of minutes, it returns the negative response in subsequent requests for the same page or image for the specified length of time. The ProxySG will not attempt to fetch the request from the OCS. Therefore, while server-side bandwidth is saved, you could receive negative responses to requests that might otherwise have been served by accessing the OCS. By default, the ProxySG does not cache negative responses. It always attempts to retrieve the object from the OCS, if it is not already in cache.
Default: 0 minutes Forcing freshness validation before
serving an object from cache
Verifies that each object is fresh upon access. Enabling this setting has a significant impact on performance because the HTTP proxy revalidates requested cached objects with the OCS before serving them to the client. This results in a negative impact on bandwidth gain. Therefore, do not enable this configuration unless absolutely required.
For enabling, select the Always check with source before serving object check box.
Default: Disabled Forcing HTTPS server certificate
validation
Always verifies the certificate of the OCS for HTTPS connections. For enabling, select the Verify server certificate for secure connections.
Default: Disabled Settings to Configure Object Caching Notes
Section B: Configuring the HTTP Proxy Performance
The above settings serve as defaults on the proxy. If you want a more granular caching policy, for example— setting the TTL for an object, use Blue Coat Content Policy Language (CPL). You can also use the VPM or CPL to bypass the cache or to prohibit caching for a specific domain or server. Refer to Volume 10: Content Policy Language Guide for more information.
Parsing HTTP meta tag headers Determines how HTTP meta tag headers are parsed in the HTML documents. The meta tags that can be enabled for parsing are:
• Cache-control meta tag
The sub-headers that are parsed when this check box is selected are: private, no-store, no-cache, max-age, s-maxage, must- revalidate, proxy-revalidate
• Expires meta tag
This directive parses for the date and time after which the document should be considered expired.
• Pragma-no-cache meta tag
This directive indicates that cached information should not be used and instead requests should be forwarded to the OCS.
Default: Disabled Allocating bandwidth on the HTTP
proxy for maintaining freshness of the objects in cache
Allows you to specify a limit to the amount of bandwidth the ProxySG uses to achieve the desired freshness. Blue Coat recommends letting the ProxySG manage bandwidth allocation, the default setting. For more information see, "Allocating Bandwidth to Refresh Objects in Cache" on page 135.
Default: Let the SG appliance manage refresh bandwidth.
Section B: Configuring the HTTP Proxy Performance
To set HTTP default object caching policy:
1. Review Table 8–2, for planning information and defaults.
2. From the Management Console, select Configuration > Proxy Settings > HTTP Proxy > Policies.
3. Set the maximum object cache size. In the Do not cache objects larger than field, enter the maximum object size to cache. The default is 1024 MB.
4. Set the negative response Time-to-Live. In the Cache negative responses for field, enter the number of minutes SGOS stores negative responses. The default is 0. 5. Force freshness validation. To always verify that each object is fresh upon
access, select the Always check with source before serving object check box. Enabling this setting has a significant impact on performance, do not enable this configuration unless absolutely required.
6. Force HTTPS server certificate validation. If you communicate with an origin content server (OCS) through HTTPS and want the OCS certificate to be verified, be sure that Verify server certificate for secure connections is selected. 7. Disable meta-tag parsing. The default is to parse HTTP meta tag headers in
HTML documents if the MIME type of the object is text/html. To disable meta-tag parsing, clear the check box for:
• Parse cache-control meta tag
The following sub-headers are parsed when this check box is selected:
private, no-store, no-cache, max-age, s-maxage, must-revalidate, proxy-revalidate.
• Parse expires meta tag
This directive parses for the date and time after which the document should be considered expired.
Section B: Configuring the HTTP Proxy Performance
• Parse pragma-no-cache meta tag
This directive indicates that cached information should not be used and instead requests should be forwarded to the OCS.
8. Click OK; click Apply.