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Integrated caching

December 13, 2018
Contributed by:  S

The integrated cache provides in-memory storage on the NetScaler appliance and serves Web content to users without requiring a round trip to an origin server. For static content, the integrated cache requires little initial setup. After you enable the integrated cache feature and perform basic setup (for example, determining the amount of NetScaler appliance memory the cache is permitted to use), the integrated cache uses built-in policies to store and serve specific types of static content, including simple Web pages and image files. You can also configure the integrated cache to store and serve dynamic content that is usually marked as non-cacheable by Web and application servers (for example, database records and stock quotes).

Note: The term Integrated Cache can be interchangeably used with AppCache; note that from a functionality point of view, both terms mean the same.

When a request or response matches the rule (logical expression) specified in a built-in policy or a policy that you have created, the NetScaler appliance performs the action associated with the policy. By default, all policies store cached objects in and retrieve them from the Default content group, but you can create your own content groups for different types of content.

To enable the NetScaler appliance to find cached objects in a content group, you can configure selectors, which match cached objects against expressions, or you can specify parameters for finding objects in the content group. If you use selectors (which Citrix recommends), configure them first, so that you can specify selectors when you configure content groups. Next, set up any content groups that you want to add, so that they are available when you configure the policies. To complete the initial configuration, create policy banks by binding each policy to a global bind point or a virtual server, or to a label that can be called from other policy banks.

You can tune the performance of the integrated cache, using methods such as pre-loading cached objects before they are scheduled to expire. To manage the handling of cached data once it leaves the NetScaler appliance, you can configure caching-related headers that are inserted into responses. The integrated cache can also act as a forward proxy for other cache servers.

Note: Integrated caching requires some familiarity with HTTP requests and responses. For information about the structure of HTTP data, see Live HTTP Headers at “http://livehttpheaders.mozdev.org/.”

How integration cache works

The integrated cache monitors HTTP and SQL requests that flow through the NetScaler appliance and compares the requests with stored policies. Depending on the outcome, the integrated cache feature either searches the cache for the response or forwards the request to the origin server. For HTTP requests, the integrated cache feature can also serve partial content from the cache in response to single byte-range and multi-part byte-range requests.

Cached data can be compressed if the client accepts compressed content. You can configure expiration times for a content group, and you can selectively expire entries in a content group.

Data that is served from the integrated cache is a cache hit, and data served from the origin is a cache miss, as described in the following table.

Transaction Type Specification
Cache Hit Responses that the NetScaler appliance serves from the cache, including: Static objects, for example, image files and static Web pages, 200 OK pages, 203 Non-Authoritative Response pages, 300 Multiple Choices pages, 301 Moved Permanently pages, 302 Found pages, 304 Not Modified pages, These responses are known as positive responses. The NetScaler appliance also caches the following negative responses: 307 Temporary Redirect pages, 403 Forbidden pages, 404 Not Found pages, 410 Gone pages. To further improve performance, you can configure the NetScaler appliance to cache additional types of content.
Storable Cache Miss For a storable cache miss, the NetScaler appliance fetches the response from the origin server, and stores the response in the cache before serving it to the client.
Non-Storable Cache Miss A non-storable cache miss is inappropriate for caching. By default, any response that contains the following status codes is a non-storable cache miss: 201, 202, 204, 205, 206 status codes, All 4xx codes, except 403, 404 and 410, 5xx status codes

Note To integrate dynamic caching with your application infrastructure, use the NITRO API to issue cache commands remotely. For example, you can configure triggers that expire cached responses when a database table is updated.

To ensure the synchronization of cached responses with the data on the origin server, you configure expiration methods. When the NetScaler appliance receives a request that matches an expired response, it refreshes the response from the origin server.

Note Citrix recommends that you synchronize the times on the NetScaler appliance and the back-end server(s).

How dynamic cache works

Dynamic caching evaluates HTTP requests and responses based on parameter-value pairs, strings, string patterns, or other data. For example, suppose that a user searches for Bug 31231 in a bug reporting application. The browser sends the following request on the user’s behalf:

GET /mybugreportingsystem/mybugreport.dll?IssuePage&RecordId=31231&Template=view&TableId=1000

Host: mycompany.net

User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9) Gecko/2008052906 Firefox/3.0

Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8

Accept-Language: en-us,en;q=0.5

. . .

In this example, GET requests for this bug reporting application always contain the following parameters:

  • IssuePage
  • RecordID
  • Template
  • TableId

GET requests do not update or alter the data, so you can configure these parameters in caching policies and selectors, as follows:

  • You configure a caching policy that looks for the string mybugreportingsystem and the GET method in HTTP requests. This policy directs matching requests to a content group for bugs.
  • In the content group for bugs, you configure a hit selector that matches various parameter-value pairs, including IssuePage, RecordID, and so on.

Note: that a browser can send multiple GET requests based on one user action. The following is a series of three separate GET requests that a browser issues when a user searches for a bug based on a bug ID.

GET /mybugreportingsystem/mybugreport.dll?IssuePage&RecordId=31231&Template=view&TableId=1000

GET /mybugreportingsystem/mybugreport.dll?IssuePage&Template=viewbtns&RecordId=31231&TableId=1000

GET /mybugreportingsystem/mybugreport.dll?IssuePage&Template=viewbody&RecordId=31231&tableid=1000

To fulfill these requests, multiple responses are sent to the user’s browser, and the Web page that the user sees is an assembly of the responses.

If a user updates a bug report, the corresponding responses in the cache should be refreshed with data from the origin server. The bug reporting application issues HTTP POST requests when a user updates a bug report. In this example, you configure the following to ensure that POST requests trigger invalidation in the cache:

  • A request-time invalidation policy that looks for the string mybugreportingsystem and the POST HTTP request method, and directs matching requests to the content group for bug reports.
  • An invalidation selector for the content group for bug reports that expires cached content based on the RecordID parameter. This parameter appears in all of the responses, so the invalidation selector can expire all relevant items in the cache.

The following excerpt shows a POST request that updates the sample bug report.

POST /mybugreportingsystem/mybugreport.dll?TransitionForm HTTP/1.1\r\n

User-Agent: Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.0) Opera 7.23 [en]\r\n

Host: mybugreportingsystem\r\n

Cookie:ttSearch.134=%23options%3Afalse%23active%23owner%3Afalse%23unowned%3Afalse%23submitter%3Afalse%23incsub%3Atrue;

Cookie2: $Version=1\r\n

. . .

\r\n

ProjectId=2&RecordId=31231&TableId=1000&TransitionId=1&Action=Update&CopyProjectId=0&ReloadForm=0&State=&RecordLockId=49873+issues+in+HTTP&F43. . .

When the NetScaler appliance receives this request, it does the following:

  • Matches the request with an invalidation policy.
  • Finds the content group that is named in the policy.
  • Applies the invalidation selector for this content group and expires all responses that match RecordID=31231.

When a user issues a new request for this bug report, the NetScaler appliance goes to the origin server for updated copies of all the responses that are associated with the report instance, stores the responses in the content group, and serves them to the user’s browser, which reassembles the report and displays it.

Configure integrated cache

To use the integrated cache, you must install the license and enable the feature. After you enable the integrated cache, the NetScaler® appliance automatically caches static objects as specified by built-in policies and generates statistics on cache behavior. (Built-in policies have an underscore in the initial position of the policy name.)

Even if the built-in policies are adequate for your situation, you might want to modify the global attributes. For example, you might want to modify the amount of NetScaler appliance memory allocated to the integrated cache.

If you would like to observe cache operation before changing settings, see “Displaying Cached Objects and Cache Statistics.”

Note The NetScaler cache is an in-memory store that is purged when you restart the appliance.

To install integrated cache license

An integrated cache license is required. For information about licenses, see information about obtaining licenses topic.

Obtain a license code from Citrix, go to the command line interface, and log in.

At the command line interface, copy the license file to the /nsconfig/license folder.

Reboot the NetScaler appliance by using the following command:

reboot

To enable integrated caching: When you enable integrated caching, the NetScaler appliance begins caching server responses. If you have not configured any policies or content groups, the built in policies store cached objects in the Default content group.

At the command prompt, type one of the following commands to enable or disable integrated caching:

‘enable ns feature IC’

To configure global attributes for caching

Global attributes apply to all cached data. You can specify the amount of NetScaler memory allocated to the integrated cache, Via header insertion, a criterion for verifying that a cached object should be served, the maximum length of a POST body permitted in the cache, whether to bypass policy evaluation for HTTP GET requests, and an action to take when a policy cannot be evaluated.

The cache memory capacity is limited only by the memory of the hardware appliance. Also, any packet engine (the central distribution hub of all incoming TCP requests) in the nCore NetScaler appliance is aware of objects cached by other packet engines in the nCore NetScaler appliance.

Note: When the default global memory limit is set as 0 and the Integrated Caching (IC) feature is enabled, the appliance does not cache any objects. For caching, you must explicitly configure the global memory limit. However, if you enable “set aaa parameter enableStaticPageCaching” option, there will be some default memory configured in the appliance. This memory is insufficient for caching large Objects and so it is necessary to assign a higher memory limit for IC. You can perform this by configuring the “set cache parameter –memLimit” command. The new setting is applied only after you save the configuration and reboot the appliance.

You can modify the global memory limit configured for caching objects. However, when you update the global memory limit to a value lower than the existing value (for example, from 10 GB to 4 GB), if a higher amount of memory (greater than 4 GB) is already being used to cache objects, the NetScaler continues using that amount of memory.

This means that even though the integrated caching limit is configured to some value, the actual limit used can be higher. This excessive memory is however released when the objects are removed from cache.

The output of the show cache parameter command indicates the configured value (memory Usage limit) and the actual value being used (memory usage limit (active value)).

At the command prompt, type:

set cache parameter [-memLimit <MBytes>] [-via <string>] [-verifyUsing <criterion>] [-maxPostLen <positiveInteger>] [-prefetchMaxPending <positiveInteger>] [-enableBypass(YES|NO)] [-undefAction (NOCACHE|RESET)]

To enable integrated caching by using the GUI:

Navigate to System > Settings, click Configure Basic Features, and select Integrated Caching.

To configure global settings for caching by using the GUI:

Navigate to Optimization > Integrated Caching, click Change Cache Settings, and configure the global settings for caching.

To set up built-in content group, pattern set, and policies for Integrated Cache:

The NetScaler appliance includes a built-in integrated caching configuration that you can use for caching content. The configuration consists of a content group called ctx_cg_poc, a pattern set called ctx_file_extensions, and a set of integrated cache policies. In the content group ctx_cg_poc, only objects that are 500 KB or smaller are cached. The content is cached for 86000 seconds, and the memory limit for the content group is 512 MB. The pattern set is an indexed array of common file extensions for file-type matching.

The following table lists the built-in integrated caching policies. By default, the policies are not bound to any bind point. You must bind them to a bind point if you want the NetScaler appliance to evaluate traffic against the policies. The policies cache objects in the ctx_cg_poc content group.

Integrated caching policy name Policy rule
_cacheVPNStaticObjects HTTP.REQ.URL.SET_TEXT_MODE(IGNORECASE).CONTAINS_INDEX("ctx_file_extensions").BETWEEN(101,150)
_cacheTCPVPNStaticObjects HTTP.REQ.URL.ENDSWITH(".css")
_cacheOCVPNStaticObjects HTTP.REQ.URL.ENDSWITH(".pdf")
_cacheWFStaticObjects HTTP.REQ.URL.ENDSWITH(".js")
_mayNoCacheReq HTTP.RES.HEADER("Content-Type").CONTAINS("application/x-javascript")
_noCacheRest TRUE

Integrated caching

December 13, 2018
Contributed by:  S

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