This page applies to Apigee and Apigee hybrid.
View Apigee Edge documentation.
Configures how cached values should be written at runtime.
The Populate Cache policy is designed for writing entries in a short-term general-purpose cache. It's used in conjunction with the Lookup Cache policy (for reading cache entries) and the Invalidate Cache 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 Response Cache policy.
Element reference
The following lists the elements you can configure on this policy.
<PopulateCache async="false" continueOnError="false" enabled="true" name="Populate-Cache-1"> <DisplayName>Populate Cache 1</DisplayName> <Properties/> <CacheKey> <Prefix/> <KeyFragment ref=""/> </CacheKey> <!-- Omit this element if you're using the included shared cache. --> <CacheResource/> <Scope>Exclusive</Scope> <ExpirySettings> <TimeoutInSeconds>300</TimeoutInSeconds> </ExpirySettings> <Source>flowVar</Source> </PopulateCache>
<PopulateCache> 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 Optionally, use the |
N/A | Required |
continueOnError |
Set to Set to |
false | Optional |
enabled |
Set to Set to |
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 |
---|---|
Presence | Optional |
Type | String |
<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>
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.
<CacheResource> element
Specifies the cache where messages should be stored.
Omit this element completely if this policy (and your corresponding LookupCache 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: |
zero or more |
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 fixed 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.
<ExpirySettings> element
Specifies when a cache entry should expire.
<ExpirySettings> <!-- use exactly one of the following child elements --> <TimeoutInSeconds ref="duration_variable">seconds_until_expiration</TimeoutInSeconds> <ExpiryDate ref="date_variable">expiration_date</ExpiryDate> <TimeOfDay ref="time_variable">expiration_time</TimeOfDay> </ExpirySettings>
Default: |
N/A |
Presence: |
Required |
Type: |
N/A |
Child elements of <ExpirySettings>
Use exactly one child element. The following table provides a description of the child elements of
<ExpirySettings>
:
Child Element | Description |
---|---|
<TimeoutInSeconds> |
The number of seconds after which a cache entry should expire. <ExpirySettings> <TimeoutInSeconds ref="var-containing-duration">expiry</TimeoutInSeconds> </ExpirySettings> This element replaces the now-deprecated |
<ExpiryDate> |
Specifies the date on which a cache entry should expire. Specify a string in the form
<ExpirySettings> <ExpiryDate ref="var-containing-date">expiry</ExpiryDate> </ExpirySettings> If the date specified is in the past, the policy will apply the maximum time-to-live to the cached entry. This maximum is 30 days. |
<TimeOfDay> |
Specifies the time of day on which a cache entry should expire.
Specify a string in the form <ExpirySettings> <TimeOfDay ref="var-containing-time">expiry</TimeOfDay> </ExpirySettings> |
You should specify only one of the possible child elements. If you specify multiple elements,
the order of precedence is:TimeoutInSeconds
, ExpiryDate
,
TimeOfDay
.
With each of the above child elements of <ExpirySettings>
,
if you specify the optional ref
attribute on the child element, the policy will
retrieve the expiry value from the named context variable. If the variable is not defined,
the policy uses the literal text value of the child element.
<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__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
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 |
Application |
API proxy name is used as the prefix. Cache key is prepended in the form orgName__envName__apiProxyName. |
Proxy |
ProxyEndpoint configuration is used as the prefix. Cache key is prepended in the form orgName__envName__apiProxyName__deployedRevisionNumber__proxyEndpointName . |
Target |
TargetEndpoint configuration is used as the prefix. Cache key prepended in the form orgName__envName__apiProxyName__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:
Cache key prepended in the form orgName__envName__apiProxyName__deployedRevisionNumber__proxyNameITargetName For example, the full string might look like this: apifactory__test__weatherapi__16__default__apiAccessToken |
<Source> element
Specifies the variable whose value should be written to the cache.
<Source>source_variable</Source>
Default: |
N/A |
Presence: |
Required |
Type: |
String |
Usage notes
Use this policy for general purpose caching. At runtime, the
<PopulateCache>
policy writes data from the variable you specified in the
<Source>
element to the cache you specified in the
<CacheResource>
element. You can use the <CacheKey>
,
<Scope>
, and <Prefix>
elements to specify a key that you
can use from the <LookupCache>
policy to retrieve the value. Use the
<ExpirySettings>
element to configure when the cached value should expire.
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 this cache, simply omit the
<CacheResource>
element.
Cache limits: Various cache limits apply, such as name and value size, total number of caches, the number of items in a cache, and expiration.
For more about the underlying data store, see Cache internals.
About cache encryption
Apigee and Apigee hybrid (version 1.4 and later): Cache and KVM data are always encrypted.
Error codes
This section describes the fault codes and error messages that are returned and fault variables that are set by Apigee when this policy triggers an error. This information is important to know if you are developing fault rules to handle faults. To learn more, see What you need to know about policy errors and Handling faults.
Runtime errors
These errors can occur when the policy executes.
Fault code | HTTP Status | Occurs when |
---|---|---|
policies.populatecache.EntryCannotBeCached |
500 |
An entry cannot be cached. The message object being cached is not an instance of a class that is Serializable. |
Deployment errors
These errors can occur when you deploy a proxy containing this policy.
Error name | Cause | Fix |
---|---|---|
InvalidCacheResourceReference |
This error occurs if the <CacheResource> element in the PopulateCache policy is set to
a name that does not exist in the environment where the API proxy is being deployed. |
build |
CacheNotFound |
The cache specified in the <CacheResource> element does not
exist. |
build |
Fault variables
These variables are set when this policy triggers an error. For more information, see What you need to know about policy errors.
Variables | Where | Example |
---|---|---|
fault.name="fault_name" |
fault_name is the name of the fault, as listed in the Runtime errors table above. The fault name is the last part of the fault code. | fault.name = "EntryCannotBeCached" |
populatecache.policy_name.failed |
policy_name is the user-specified name of the policy that threw the fault. | populatecache.POP-CACHE-1.failed = true |
Example error response
{ "fault": { "faultstring": "[entry] can not be cached. Only serializable entries are cached.", "detail": { "errorcode": "steps.populatecache.EntryCannotBeCached" } } }
Example fault rule
<FaultRule name="Populate Cache Fault"> <Step> <Name>AM-EntryCannotBeCached</Name> <Condition>(fault.name Matches "EntryCannotBeCached") </Condition> </Step> <Condition>(populatecache.POP-CACHE-1.failed = true) </Condition> </FaultRule>