ResponseCache policy

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Caches data from a backend resource, reducing the number of requests to the resource. As apps make requests to the same URI, you can use this policy to return cached responses instead of forwarding those requests to the backend server. The ResponseCache policy can improve your API's performance through reduced latency and network traffic.

You'll likely find ResponseCache most useful when backend data used by your API is updated only periodically. For example, imagine you have an API that exposes weather report data refreshed only every ten minutes. By using ResponseCache to return cached responses between refreshes, you can decrease the number of requests reaching the backend. This also reduces the number of network hops.

For general purpose short-term caching, considering using the Populate Cache policy. That policy is used in conjunction with the Lookup Cache policy (for reading cache entries) and the Invalidate Cache policy (for invalidating entries).

Samples

http://{org_name}-test.apigee.net/weather/forecastrss?w=23424778

<ResponseCache name="ResponseCache">
    <CacheKey>
        <KeyFragment ref="request.queryparam.w" />
    </CacheKey>
    <ExpirySettings>
        <TimeoutInSeconds>600</TimeoutInSeconds>
    </ExpirySettings>
</ResponseCache>

http://{org_name}-test.apigee.net/weather/forecastrss?w=23424778

'http://{org_name}-test.apigee.net/weather/forecastrss?w=23424778' -H "bypass-cache:true"

<ResponseCache name="ResponseCache">
    <CacheKey>
        <KeyFragment ref="request.queryparam.w" />
    </CacheKey>
    <!-- Explicitly refresh the cached response -->
    <SkipCacheLookup>request.header.bypass-cache = "true"</SkipCacheLookup>
    <ExpirySettings>
        <TimeoutInSeconds>600</TimeoutInSeconds>
    </ExpirySettings>
</ResponseCache>

Element reference

The element reference describes the elements and attributes of the policy.

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<ResponseCache async="false" continueOnError="false" enabled="true" name="Response-Cache-1">
    <DisplayName>Response Cache 1</DisplayName>
    <Properties/>
    <CacheKey>
        <Prefix/>
        <KeyFragment ref="request.uri" />
    </CacheKey>
    <Scope>Exclusive</Scope>
    <ExpirySettings>
        <ExpiryDate/>
        <TimeOfDay/>
        <TimeoutInSeconds ref="flow.variable.here">300</TimeoutInSeconds>
    </ExpirySettings>
    <CacheResource>cache_to_use</CacheResource>
    <CacheLookupTimeoutInSeconds/>
    <ExcludeErrorResponse/>
    <SkipCacheLookup/>
    <SkipCachePopulation/>
    <UseAcceptHeader/>
    <UseResponseCacheHeaders/>
</ResponseCache>

<ResponseCache> attributes

<ResponseCache async="false" continueOnError="false" enabled="true" name="Response-Cache-1">

The following table describes attributes that are common to all policy parent elements:

<DisplayName> element

Use in addition to the name attribute to label the policy in the management UI proxy editor with a different, natural-language name.

<DisplayName>Policy Display Name</DisplayName>

<CacheKey> element

Configures a unique pointer to a piece of data stored in the cache.

Cache keys are limited to a size of 2 KB.

<CacheKey>
    <Prefix>string</Prefix>
    <KeyFragment ref="variable_name" />
    <KeyFragment>literal_string</KeyFragment>
</CacheKey>

<CacheKey> constructs the name of each piece of data stored in the cache. The key is often set using a value from entity headers or query params. In those cases, you would have the element's ref attribute specify a variable containing the key value.

At runtime, <KeyFragment> values are prepended with either the <Scope> element value or <Prefix> value. For example, the following results in a cache key of UserToken__apiAccessToken__<value_of_client_id>:

<CacheKey>
    <Prefix>UserToken</Prefix>
    <KeyFragment>apiAccessToken</KeyFragment>
    <KeyFragment ref="request.queryparam.client_id" />
</CacheKey>

You use the <CacheKey> element in conjunction with <Prefix> and <Scope>. For more information, see Working with cache keys.

<CacheLookupTimeoutInSeconds> element

Specifies the number of seconds after which an unsuccessful cache lookup will be considered a cache miss. If this occurs, flow resumes along the cache-miss path.

<CacheLookupTimeoutInSeconds>30</CacheLookupTimeoutInSeconds>

<CacheResource> element

Specifies the cache where messages should be stored. Omit this element to use the included shared cache. You should specify a CacheResource by name if you wish to be able to administratively clear entries contained in the cache. For more on that, see Caches.

<CacheResource>cache_to_use</CacheResource>

For more about configuring caches, see Creating and editing an environment cache.

<CacheKey>/<KeyFragment> element

Specifies a value that should be included in the cache key, creating a namespace for matching requests to cached responses.

<KeyFragment ref="variable_name"/>
<KeyFragment>literal_string</KeyFragment>

This can be a key (a static name that you provide) or a value (a dynamic entry set by referencing a variable). All specified fragments combined (plus the prefix) are concatenated to create the cache key.

<KeyFragment>apiAccessToken</KeyFragment>
<KeyFragment ref="request.queryparam.client_id" />

You use the <KeyFragment> element in conjunction with <Prefix> and <Scope>. For more information, see Working with cache keys.

Attributes

<CacheKey>/<Prefix> element

Specifies a value to use as a cache key prefix.

<Prefix>prefix_string</Prefix>

Use this value instead of <Scope> when you want to specify your own value rather than a <Scope> -enumerated value. If defined, <Prefix> prepends the cache key value for entries written to the cache. A <Prefix> element value overrides a <Scope> element value.

You use the <Prefix> element in conjunction with <CacheKey> and <Scope>. For more information, see Working with cache keys.

<ExcludeErrorResponse> element

Currently, by default, this policy caches HTTP responses with any possible Status code. That means both success and error responses are cached. For example, responses with both 2xx and 3xx status codes are cached by default.

Set this element to true if you do not wish to cache target responses with HTTP error status codes; only responses with status codes from 200 to 205 will be cached if this element is true. These are the only HTTP status codes that Edge counts as "success" codes, and you cannot change this association.

For a discussion of Response Cache patterns in which this element is useful, see this community post.

Note: In a future release (to be determined), the default setting of this element will change to true. See Apigee Release Notes for details.

<ExcludeErrorResponse>true</ExcludeErrorResponse>

<ExpirySettings> element

Specifies when a cache entry should expire. When present, <TimeoutInSeconds> overrides both <TimeOfDay> and <ExpiryDate>.

<ExpirySettings>
  <TimeOfDay ref="time_variable">expiration_time</TimeOfDay>
  <TimeoutInSeconds ref="duration_variable">seconds_until_expiration</TimeoutInSeconds>
  <ExpiryDate ref="date_variable">expiration_date</ExpiryDate>
</ExpirySettings>

<ExpirySettings>/<ExpiryDate> element

Specifies the date on which a cache entry should expire. Use the form mm-dd-yyyy. When present, this element's sibling, <TimeoutInSeconds>, overrides <ExpiryDate>.

<ExpirySettings>
    <ExpiryDate ref="{date_variable}">expiration_date</ExpiryDate>
</ExpirySettings>

Attributes

<ExpiryDate ref="" />

<ExpirySettings>/<TimeOfDay> element

The time of day at which a cache entry should expire. Use the form hh:mm:ss . When present, this element's sibling, <TimeoutInSeconds>, overrides <TimeOfDay>.

Enter time of day in the format HH:mm:ss, where HH represents the hour on a 24-hour clock. For example, 14:30:00 for 2:30 in the afternoon.

For the time of day, the default locale and time zone will vary depending on where the code is running (which isn't knowable when you configure the policy). For information on configuring your locale, see Creating and editing an environment cache.

<ExpirySettings>
    <TimeOfDay ref="time_variable">expiration_time</TimeOfDay>
</ExpirySettings>

Attributes

<ExpirySettings>/<TimeoutInSec> element

The number of seconds after which a cache entry should expire.

<ExpirySettings>/<TimeoutInSeconds> element

The number of seconds after which a cache entry should expire. When present, this element overrides its siblings, <TimeOfDay> and <ExpiryDate>.

<ExpirySettings>
    <TimeoutInSeconds ref="duration_variable">seconds_until_expiration</TimeoutInSeconds>
</ExpirySettings>

Note: Provide a default timeout value to use if the ref does not receive a value from the duration_variable.

Attributes

<Scope> element

Enumeration used to construct a prefix for a cache key when a <Prefix> element is not provided in the <CacheKey> element.

<Scope>scope_enumeration</Scope>

The <Scope> setting determines a cache key that is prepended according to the <Scope> value. For example, a cache key would take the following form when scope is set to Exclusive : orgName__envName__apiProxyName__deployedRevisionNumber__proxy|TargetName__ [ serializedCacheKey ].

If a <Prefix> element is present in <CacheKey>, it supersedes a <Scope> element value. Valid values include the enumerations below.

You use the <Scope> element in conjunction with <CacheKey> and <Prefix>. For more information, see Working with cache keys.

Acceptable values

apifactory__test__weatherapi__16__default__apiAccessToken

<SkipCacheLookup> element

Defines an expression that, if it evaluates to true at runtime, specifies that cache lookup should be skipped and the cache should be refreshed. See also this video on the use of SkipCacheLookup.

<SkipCacheLookup>variable_condition_expression</SkipCacheLookup>

From the following example, if the bypass-cache variable is set to true in an incoming header, cache lookup is skipped and the cache is refreshed.

<SkipCacheLookup>request.header.bypass-cache = "true"</SkipCacheLookup>

<SkipCachePopulation> element

Defines an expression that, if it evaluates to true at runtime, specifies that a write to the cache should be skipped. See also this video on the use of SkipCachePopulation.

<SkipCachePopulation>variable_condition_expression</SkipCachePopulation>

For example, the following would skip the cache write if the response status code was 400 or higher:

<SkipCachePopulation>response.status.code >= 400</SkipCachePopulation>

<UseAcceptHeader> element

Set to true to have a response cache entry's cache key appended with values from response Accept headers.

Edge uses the Accept, Accept-Encoding, Accept-Language and Accept-Charset request headers when calculating the cache key. This approach prevents a client from getting a media type they did not ask for.

For example, consider if two requests come in from the same URL, where the first request accepts gzip and the second does not. The first request will be cached, and the cached entry will (probably) be a gzipped response. The second request will read the cached value and may then return a gzipped entry to a client that is not capable of reading gzip.

See Configuring a cache key for more.

<UseAcceptHeader>false</UseAcceptHeader>

<UseResponseCacheHeaders> element

Set to true to have HTTP response headers considered when setting the "time to live" (TTL) of the response in the cache. When this is true, Edge considers the values of the following response headers, comparing the values with those set by <ExpirySettings> when setting time to live:

• Cache-Control s-maxage
• Cache-Control max-age
• Expires

See Setting cache entry expiration for more details.

<UseResponseCacheHeaders>false</UseResponseCacheHeaders>

Usage notes

The maximum size for each cached object is 256 KB. (For detailed information on how Edge processes cache, see Cache internals.)

Through configuration in the ResponseCache policy, you can have Edge include HTTP response headers in setting cache entry expiration and cache keys. This section describes you can use the policy with headers to manage cache expiration and cache keys.

For more about how Edge handles response headers with the ResponseCache policy, see Support for HTTP response headers.

Setting cache entry expiration

As with the Populate Cache policy, you can set a response cache entry's expiration (its time to live) using the <ExpirySettings> element. In the ResponseCache policy, you can also have Edge consider response headers when they're present.

To use response headers, you set the <UseResponseCacheHeaders> element value to true. That setting causes Edge to consider the response headers, compare them with the value set by <ExpirySettings>, then use the lowest value between the two. When considering the response headers, Edge chooses the value available as described in the following:

For example, imagine a response is cached with the following values:

• No Cache-Control s-maxage value
• A Cache-Control max-age value of 300
• An Expires date in three days
• An <ExpirySettings> TimeoutInSeconds value of 600.

In this case, the Cache-Control max-age value would be used for the TTL because it is lower than the <ExpirySettings> value and because there is no Cache-Control s-maxage value (which takes precedence over max-age).

Configuring a cache key

As with general purpose cache policies such as the Populate Cache policy, with ResponseCache you use <CacheKey> and <Scope> elements to configure cache key creation for cache entries. With ResponseCache you can also make cache keys more meaningful by having response Accept headers appended to key values.

For general information about configuring cache keys, see Working with cache keys. For information about using Accept headers, see <UseAcceptHeader>.

About cache encryption

Edge for Public Cloud: Cache is encrypted only in PCI- and HIPAA-enabled organizations. Encryption for those organizations is configured during organization provisioning.

Flow variables

The following predefined Flow variables are populated when a ResponseCache policy is executed. For more information about Flow variables, see Variables reference.

Error codes

This section describes the error messages and flow variables that are set when this policy triggers an error. This information is important to know if you are developing fault rules for a proxy. To learn more, see What you need to know about policy errors and Handling faults.

Error code prefix

N/A

Runtime errors

This policy does not throw any runtime errors.

Deployment errors

These errors can occur when you deploy a proxy containing this policy.

Fault variables

N/A

Example error response

N/A

Schema

Each policy type is defined by an XML schema (.xsd). For reference, policy schemas are available on GitHub.