Mule 3.9: Using Cache Scope to Avoid Parallel Processing of the same Mule Application

In this article, I will explain how to implement a logic in Mule ESB that will avoid parallel processing or simultaneously running of the same mule application. 

This Mule Application is triggered via HTTP GET Request. Once there's a new request, it will create a variable #[flowVars.correlationId], which the value came from #[message.rootId]. This ID is a unique identifier of a particular Mule process and in this application, it will be stored inside the Cache Scope as a payload using the Transform Message { correlationId: flowVars.correlation } (Map Object Data Type). Then after that scope, we have a Choice Router that will determine if there's an existing running process or not by checking if the #[payload.correlationId == flowVars.correlationId] (TRUE means there's no cached data yet) response an HTTP status 200, if FALSE return HTTP status 409 Conflict.

Take note that the #[payload.correlationId] value will always come from the Cache Scope(Object-Store) if there's a cached data, otherwise, it will cache and return the #[flowVars.correlationId] value.

<?xml version="1.0" encoding="UTF-8"?>

<mule xmlns:http="http://www.mulesoft.org/schema/mule/http" xmlns:scripting="http://www.mulesoft.org/schema/mule/scripting" xmlns:tracking="http://www.mulesoft.org/schema/mule/ee/tracking" xmlns:db="http://www.mulesoft.org/schema/mule/db"
xmlns:file="http://www.mulesoft.org/schema/mule/file"
xmlns:dw="http://www.mulesoft.org/schema/mule/ee/dw"
xmlns:ee="http://www.mulesoft.org/schema/mule/ee/core"
xmlns="http://www.mulesoft.org/schema/mule/core" xmlns:doc="http://www.mulesoft.org/schema/mule/documentation"
xmlns:spring="http://www.springframework.org/schema/beans" 
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.mulesoft.org/schema/mule/db http://www.mulesoft.org/schema/mule/db/current/mule-db.xsd
http://www.mulesoft.org/schema/mule/file http://www.mulesoft.org/schema/mule/file/current/mule-file.xsd
http://www.mulesoft.org/schema/mule/ee/dw http://www.mulesoft.org/schema/mule/ee/dw/current/dw.xsd
http://www.mulesoft.org/schema/mule/ee/core http://www.mulesoft.org/schema/mule/ee/core/current/mule-ee.xsd
http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-current.xsd
http://www.mulesoft.org/schema/mule/core http://www.mulesoft.org/schema/mule/core/current/mule.xsd
http://www.mulesoft.org/schema/mule/ee/tracking http://www.mulesoft.org/schema/mule/ee/tracking/current/mule-tracking-ee.xsd
http://www.mulesoft.org/schema/mule/http http://www.mulesoft.org/schema/mule/http/current/mule-http.xsd
http://www.mulesoft.org/schema/mule/scripting http://www.mulesoft.org/schema/mule/scripting/current/mule-scripting.xsd">


    <ee:object-store-caching-strategy name="Caching_Strategy" doc:name="Caching Strategy">
        <managed-store storeName="correlation_id_store" maxEntries="-1" entryTTL="18000000" expirationInterval="18000000"/>
    </ee:object-store-caching-strategy>
    <http:listener-config name="HTTP_Listener_Configuration" host="0.0.0.0" port="8081" basePath="/api" doc:name="HTTP Listener Configuration"/>

    <flow name="pf-avoid-parallel-process">
        <http:listener config-ref="HTTP_Listener_Configuration" path="/process" allowedMethods="GET" doc:name="HTTP"/>
        <set-variable variableName="correlationId" value="#[message.rootId]" doc:name="Variable Set correlationId"/>
        <set-payload value="&quot;Caching Correlation Id&quot;" doc:name="Set Payload As String"/>
        <ee:cache doc:name="Cache" cachingStrategy-ref="Caching_Strategy">
            <dw:transform-message doc:name="Transform Message">
                <dw:set-payload><![CDATA[%dw 1.0
%output application/java
---
{
correlationId: flowVars.correlationId
}]]></dw:set-payload>
            </dw:transform-message>
        </ee:cache>
        <choice doc:name="Choice correlationId?">
            <when expression="#[payload.correlationId == flowVars.correlationId]">
                <scripting:transformer doc:name="Groovy Sleep(15000)">
                    <scripting:script engine="Groovy"><![CDATA[sleep(15000)]]></scripting:script>
                </scripting:transformer>
            <ee:invalidate-cache doc:name="Invalidate Cache" cachingStrategy-ref="Caching_Strategy"/>
                <dw:transform-message doc:name="Transform Message 200 JSON Response">
                    <dw:set-payload><![CDATA[%dw 1.0
%output application/json
---
{
correlationId: flowVars.correlationId,
status: "COMPLETED"
}]]></dw:set-payload>
                </dw:transform-message>
            </when>
            <otherwise>
                <logger  level="INFO" doc:name="Logger"/>
                <dw:transform-message doc:name="Transform Message 409 JSON Reponse">
                    <dw:set-payload><![CDATA[%dw 1.0
%output application/json
---
{
status: "Error",
message: "There's already running process with correlationId " ++ payload.correlationId ++ "."
}]]></dw:set-payload>
                    <dw:set-property propertyName="http.status"><![CDATA[%dw 1.0
%output application/java
---
409]]></dw:set-property>
                </dw:transform-message>
            </otherwise>
        </choice>
        <logger message="#[flowVars.correlationId] - End Of Process" level="INFO" doc:name="Logger"/>
    </flow>

</mule>

OBJECT-STORE-CACHING-STRATEGY(Cache Scope Configuration):

For more information regarding this configuration, see https://docs.mulesoft.com/mule-user-guide/v/3.9/cache-scope#configobjstore

<ee:object-store-caching-strategy name="Caching_Strategy" doc:name="Caching Strategy">
  <managed-store storeName="correlation_id_store" 
  maxEntries="-1" 
  entryTTL="18000000" 
  expirationInterval="18000000"/>
</ee:object-store-caching-strategy>

CACHE SCOPE: This scope will always store the returned payload from the Transform Message which is { correlationId: flowVars.correlationId }. Also, note that the payload before the Cache Scope should be a STRING Data Type otherwise it will not work.

<set-payload value="&quot;Caching Correlation Id&quot;" doc:name="Set Payload As String"/>
<ee:cache doc:name="Cache" cachingStrategy-ref="Caching_Strategy">
    <dw:transform-message doc:name="Transform Message">
        <dw:set-payload><![CDATA[%dw 1.0
            %output application/java
            ---
            {
                correlationId: flowVars.correlationId
            }]]>
        </dw:set-payload>
    </dw:transform-message>
</ee:cache>

INVALIDATE-CACHE: Invalidate the cache means clearing the cached data exists in the object store.

<ee:invalidate-cache doc:name="Invalidate Cache" 
 cachingStrategy-ref="Caching_Strategy"/>

CHOICE (Choice correlationId?): A Choice Router with a condition #[payload.correlationId == flowVars.correlationId] if validated as TRUE, it will execute the Groovy Sleep(15000), Invalidate Cache and response a HTTP Status 200 OK with JSON payload indicating that the process completed. if FALSE, return HTTP Status 409 Conflict with JSON payload indicating that there is a currently running process.

<choice doc:name="Choice correlationId?">
     <when expression="#[payload.correlationId == flowVars.correlationId]">
           <scripting:transformer doc:name="Groovy Sleep(15000)">
                <scripting:script engine="Groovy"><![CDATA[sleep(15000)]]></scripting:script>
           </scripting:transformer>
           <ee:invalidate-cache doc:name="Invalidate Cache" cachingStrategy-ref="Caching_Strategy"/>
           <dw:transform-message doc:name="Transform Message 200 JSON Response">
               <dw:set-payload><![CDATA[%dw 1.0
                    %output application/json
                    ---
                    {
                        correlationId: flowVars.correlationId,
                        status: "COMPLETED"
                    }]]>
             </dw:set-payload>
            </dw:transform-message>
            </when>
            <otherwise>
                <dw:transform-message doc:name="Transform Message 409 JSON Reponse">
                    <dw:set-payload><![CDATA[%dw 1.0
                      %output application/json
                      ---
                      {
                          status: "Error",
                          message: "There's already running process with correlationId " ++ payload.correlationId ++ "."
                      }]]>
                  </dw:set-payload>
                    <dw:set-property propertyName="http.status"><![CDATA[%dw 1.0
                      %output application/java
                      ---
                      409]]>
                  </dw:set-property>
                </dw:transform-message>
             </otherwise>
</choice>

TEST RESULT:

Triggered the API on the Postman > First Tab. The Groovy Transformer with Sleep(15000) code will be executed causing a 15 seconds hold of the process.

Retrigger the API on the Postman > Second Tab resulted to a HTTP 409 Conflict with JSON response message indicating that there is a currently running process.

Retrigger the API on the Postman > Second Tab after 15 seconds resulted to a HTTP 200 OK with JSON response message indicating that the process completes.