LookupCache policy

This page applies to Apigee and Apigee hybrid.

View Apigee Edge documentation.

Configures how cached values should be retrieved at runtime.

This policy is intended for use in general purpose short-term caching. It is used in conjunction with the PopulateCache policy (for writing entries) and the InvalidateCache policy (for invalidating entries).

This policy is an Extensible policy and use of this policy might have cost or utilization implications, depending on your Apigee license. For information on policy types and usage implications, see Policy types.

For caching the responses of backend resources, see the ResponseCache policy.

Element reference

The following lists the elements you can configure on this policy.

<LookupCache async="false" continueOnError="false" enabled="true" name="Lookup-Cache-1">
    <DisplayName>Lookup Cache 1</DisplayName>
    <Properties/>
    <CacheKey>
        <Prefix/>
        <KeyFragment ref=""/>
    </CacheKey>
    <!-- Omit this element if you're using the included shared cache. -->
    <CacheResource/>
    <CacheLookupTimeoutInSeconds/>
    <Scope>Exclusive</Scope>
    <AssignTo>flowVar</AssignTo>
</LookupCache>

A shared cache is included by default. To use the shared cache, omit the <CacheResource> element in this policy configuration.

For more about the underlying data store, see Cache internals. For more about configuring caches, see General purpose caching.

<LookupCache> attributes

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

Attribute	Description	Default	Presence
name	The internal name of the policy. The value of the name attribute can contain letters, numbers, spaces, hyphens, underscores, and periods. This value cannot exceed 255 characters. Optionally, use the <DisplayName> element to label the policy in the management UI proxy editor with a different, natural-language name.	N/A	Required
continueOnError	Set to false to return an error when a policy fails. This is expected behavior for most policies. Set to true to have flow execution continue even after a policy fails. See also: Fault rules are triggered ONLY in an error state (about continueOnError) Handling faults within the current flow	false	Optional
enabled	Set to true to enforce the policy. Set to false to turn off the policy. The policy will not be enforced even if it remains attached to a flow.	true	Optional
async	This attribute is deprecated.	false	Deprecated

<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>

Default	N/A If you omit this element, the value of the policy's name attribute is used.
Presence	Optional
Type	String

<AssignTo> element

Specifies the variable where the cache entry is assigned after it has been retrieved from the cache. The variable must be writable. If the cache lookup doesn't retrieve a value, the variable will not be set.

<AssignTo>variable_to_receive_cached_value</AssignTo>

Default:	N/A
Presence:	Required
Type:	String

<CacheKey> element

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

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

Default:	N/A
Presence:	Required
Type:	N/A

<CacheKey> constructs the name of each piece of data stored in the cache.

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>12</CacheLookupTimeoutInSeconds>

Default:	12
Presence:	Optional
Type:	Integer

<CacheResource> element

Specifies the cache where messages should be stored.

Omit this element completely if this policy (and your corresponding PopulateCache and InvalidateCache policies) is using the included shared cache.

<CacheResource>cache_to_use</CacheResource>

Default:	N/A
Presence:	Optional
Type:	String

For more about configuring caches, see General purpose caching.

<CacheKey>/<KeyFragment> element

Specifies a value that should be included in the cache key. Specify a variable to de-reference with the ref attribute, or a fixed value.

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

Default:	N/A
Presence:	Optional
Type:	N/A

At runtime, Apigee creates the cache key by prepending the value obtained from the <Scope> element or the <Prefix> element, to a concatenation of the resolved values of each of the <KeyFragment> elements. For more information, see Working with cache keys.

Attributes

Attribute	Type	Default	Required	Description
ref	string		No	The variable from which to get the value. Should not be used if this element contains a literal value.

<CacheKey>/<Prefix> element

Specifies a value to use as a cache key prefix.

<Prefix>prefix_string</Prefix>

Default:	N/A
Presence:	Optional
Type:	String

A <Prefix> element overrides any <Scope> element.

At runtime, Apigee creates the cache key by prepending the value obtained from the <Scope> element or the <Prefix> element, to a concatenation of the resolved values of each of the <KeyFragment> elements. For more information, see Working with cache keys.

<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>

Default:	"Exclusive"
Presence:	Optional
Type:	String

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__applicationName__deployedRevisionNumber__proxy|TargetName__ [ serializedCacheKey ].

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

For more information, see Working with cache keys.

Acceptable values

Global	Cache key is shared across all API proxies deployed in the environment. Cache key is prepended in the form orgName __ envName __. If you define a <CacheKey> entry with the <KeyFragment> apiAccessToken and a <Global> scope, each entry is stored as orgName__envName__apiAccessToken, followed by the serialized value of the access token. For an API proxy deployed in an environment called 'test' in an organization called 'apifactory', access tokens would be stored under the following cache key: apifactory__test__apiAccessToken.
Application	API proxy name is used as the prefix. Cache key is prepended in the form orgName__envName__applicationName.
Proxy	ProxyEndpoint configuration is used as the prefix. Cache key is prepended in the form orgName__envName__applicationName__deployedRevisionNumber__proxyEndpointName .
Target	TargetEndpoint configuration is used as the prefix. Cache key prepended in the form orgName__envName__applicationName__deployedRevisionNumber__targetEndpointName .
Exclusive	Default. This is the most specific, and therefore presents minimal risk of namespace collisions within a given cache. Prefix is one of two forms: If the policy is attached to the ProxyEndpoint flow, prefix is of the form ApiProxyName_ProxyEndpointName. If the policy is attached at TargetEndpoint, prefix is of the form ApiProxyName_TargetName. Cache key prepended in the form orgName__envName__applicationName__deployedRevisionNumber__proxyNameITargetName For example, the full string might look like this: apifactory__test__weatherapi__16__default__apiAccessToken .

Usage notes

Use this policy for general-purpose caching. At runtime, the LookupCache policy retrieves a value from the cache, assigning the value to the variable you specify with the AssignTo element (if no value is retrieved, the variable will not be set). It looks for the value based on a cache key created through configuration that combines the CacheKey and Scope elements. In other words, to retrieve a particular value added to the cache by a PopulateCache policy, your LookupCache policy must have cache key-related elements configured in the same way as the PopulateCache policy.

General purpose caching with the PopulateCache policy, LookupCache policy, and InvalidateCache policy uses either a cache you configure or a shared cache that's included by default. In most cases, the underlying shared cache should meet your needs. To use the default cache, simply omit the <CacheResource> element.

For more about configuring caches, see General purpose caching. For more about the underlying data store, see Cache internals.

Flow variables

Flow variables can be used to configure dynamic runtime behavior for policies and flows, based on HTTP headers or message content, or the context available in the Flow. For more information about flow variables, see Flow variables reference.

The following predefined Flow variables are available after you customize the behavior of the cache you define in a LookupCache policy.

Variables	Type	Permission	Description
lookupcache.{policy-name}.cachename	String	Read-Only	Returns the cache name used in the policy.
lookupcache.{policy-name}.cachekey	String	Read-Only	Returns the key used.
lookupcache.{policy-name}.cachehit	Boolean	Read-Only	True if the policy found a value for the specified cache key.
lookupcache.{policy-name}.assignto	String	Read-Only	Returns the variable to which cache is assigned.

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.

Tip: Need help resolving an error? Click in the Fix column for detailed troubleshooting information.

Error name	Cause	Fix
InvalidCacheResourceReference	This error occurs if the <CacheResource> element is set to a name which does not exist in the environment where the API proxy is being deployed.
InvalidTimeout	If the <CacheLookupTimeoutInSeconds> element is set to a negative number, then the deployment of the API proxy fails.
CacheNotFound	This error occurs if the specific cache mentioned in the error message has not been created on a specific Message Processor component.

Fault variables

N/A

Example error response

N/A