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This section specifies guidelines and recommendations to help you design, develop, test and deploy WSO2 solutions that provide enterprise service bus capabilities. 


Implementing enterprise integration patterns (EIPs)

For information on how you can simulate patterns from the Enterprise Integration Patterns catalog using various constructs of WSO2 Enterprise Integrator, see Enterprise Integration Patterns with WSO2 Enterprise Integrator.


Creating a tooling project

  • When you start WSO2 Enterprise Integrator Tooling, a default workspace is created to store your projects. Change the default workspace location to a preferred location that you can easily access. For information on how to change the default workspace, see Switching workspaces.
  • When you create a new project, it is created in a default location. You can change the default project location to a preferred location in a manner similar to changing the default workspace.
  • Create a Maven Multi Module (MMM) project to group the projects of a specific use case.
  • When you create the project structure, add it to source control such as SVN or Git.
  • Use the source control command line tools to interact with files.
  • When you create projects, ensure that you follow the standard Maven naming convention. For more information, see Naming Guidelines.
  • Make sure you follow the proper naming convention when you define the groupid, artifactid and version. For example, you can specify a name such as org.acme.integration.sampleesb-demo-project1.0.0.

Creating artifacts

  • When you create an artifact, use a proper naming convention from the start.
  • If an ESB project contains many artifacts related to multiple use cases, name the artifacts by prefixing or post fixing the use case name. 
  • Create specific ESB projects for specific use cases. This makes it easy to manage the code/project.
  • Design the ESB logic into highly cohesive and loosely coupled modules.
  • Avoid creating large, complex mediation code as much as possible. Always follow the separation of concerns design principle, and split lengthy logic into separate mediation components
  • When you have a common set of code, implement it in a sequence or a template that can be reused. For more information, see Sequence Template.
  • When you reference endpoints and policies, use the Registry to externalize the references so that the references can be easily used across environments. For more information, see Managing ESB projects across environments
  • Use Secure Vault to hide sensitive information such as passwords in configuration files.

Naming artifacts

When you create a project structure, be sure to follow the naming convention described in the table below:


The runtime server of your project is shared with other projects. Therefore, ensure that you specify a unique name for artifacts to avoid conflict with artifacts of other projects. Although you might not see any conflicts at the start of a project, it is possible for conflicts to arise when you have multiple projects.

Project nameThe root directory of the project source code<ProjectName>StudentInformationSystem
Sub modules (common)ESB/DSS projects<Project><ModuleName>StudentInformationSystemDataService
FoldersCustom folders that you create to categorize resources in registry resource projects

Specify the folder structure for registry resources



Source filesSource files such as sequences, proxy services.<FileName><Type>.<Extension>GetStudentSequence, SimpleStockQuoteProxyService

Listed below are the best practices you should follow when working with source code: 

  • When you write code, ensure that you follow a standard file naming convention to improve the readability and organisation of the code. There are different conventions depending on the programming language you use. Follow the naming convention provided below when you name WSO2 source files:


    For example, Student_Student_Sequence.xml, Stocks_StockQuote_FileInbound.xml

  • You can use a general naming convention for other known source files. If applicable, you can use a class naming convention that includes the business domain so that it is self explanatory. For example,
    For more information on naming conventions, see the library article WSO2 Developer Studio - Development and Deployment Best Practices.

Using mediators

  • Using the Log mediator:

    • In an ideal production environment where the server is running smoothly, log entries should not be written to the log file. However, if the server experiences problems, there should be sufficient entries written to the log file to understand the problem.

    • In the development phase, you should use Log mediators in the message flow as checkpoints.

    • If you are using the Log mediator to track and troubleshoot the message flow, set the log level to DEBUG.

    • If you are in a development environment, ensure that you set the global log level of org.apache.synapse.mediators.builtin.LogMediator to DEBUG.

    • If you are in a production environment, ensure that you set the global log level of org.apache.synapse.mediators.builtin.LogMediator to INFO. Setting the log level to INFO allows you to troubleshoot the message flow in production whenever required without having to go through the synapse configuration.

    • You should use Log mediators in the FaultSequence to capture information about errors that occur. The logs entries printed via the FaultSequences will be available in the wso2carbon.log that is in the main log file.

  • Using class/custom mediators:

    • You should not write a Class mediator if the intended functionality can be achieved using the enterprise service bus capabilities of WSO2 Enterprise Integrator. Following this practice avoids maintenance overhead. If you want to see detailed information on the functionality of each built-in mediator of WSO2 Enterprise Integrator, see the Mediator catalog.

    • If you are writing a Class mediator, ensure that you have a good understanding of the performance impact and possible memory leaks so that you can take these into consideration.

    • Be sure to specify a proper package name for Class  mediators
    • Be sure to apply all java naming conventions and code best practices when you write the code for Class mediators.

  • When you are adding the last mediator in a sequence, make sure to use one of the following mediators depending on the scenario:

    • Use the Respond mediator as the last mediator if you want the message to be sent back to the client.

    • Use the Send Mediator as the last mediator if you want the message to be sent to a specific endpoint. If you want to mediate the message after it is sent, you can use the Clone mediator to make two copies of the message and process them separately in order to avoid conflicts.

    • Use the Drop mediator as the last mediator if you want to stop the mediation flow at a particular point (e.g., when a filter condition is not met).

    • Use the Loopback mediator as the last mediator if you want the message to be moved from the InSequence to the OutSequence.


      The Loopback mediator prevents the execution of subsequent mediators in the InSequence.

    • Use the Store mediator as the last mediator if you want to enqueue messages to a message store.

  • Using Call vs. Callout vs. Send.
    • You can use either the Call mediator or the Callout mediator or the Send mediator to send a message to an endpoint.

    • If you use the Send mediator to send a message, the response goes to the OutSequence (or to the specified receiving sequence).
    • If you use the Call mediator to send a message, the response goes to the next mediator placed right after the send mediator in the mediation flow.
    • The use of Call mediator is recommended for service chaining scenarios.
    • Both the Send mediator and Call mediator use the non blocking transport. Therefore, in terms of performance there is no difference between the Send mediator and the Call mediator.
    • Behaviour of the Callout mediator is similar to the Call mediator, but it uses the blocking transport to send the message out. Therefor, in terms of performance, Callout mediator is not as good as the Call mediator or Send mediator. If there are scenarios where blocking behaviour is required, you can use the Callout mediator. For example, see JMS Transactions.


      You should not use the Callout mediator unless there is a specific requirement for blocking behaviour in the underlying transport implementation.

      The Callout mediator functionality has been merged into the Call mediator in WSO2 Enterprise Integrator. Therefore, you can use the Call mediator and set the blocking flag appropriately to switch between non-blocking and blocking behaviour.

 The following diagram illustrates a proxy/REST API with a Send mediator:


         The following diagram illustrates a proxy/REST API with a Call/Callout mediator:


  • You should not specify any mediator after the Send Mediator or the Respond Mediator.
    A message flow must end from these two mediators. Here, the message flow does not mean the current sequence. If you have these two mediators in a sub-sequence that gets called from a parent sequence, then once the message returns from the sub-sequence to the parent, the parent sequence should not include any mediator after the call to the sub-sequence. If you include a mediator after these two mediators, it can cause unusual behaviour in the message flow.

    The following diagram illustrates an incorrect use of the Send mediator:


  The following diagram illustrates the correct use of the Send mediator:

  • Do not use DB mediators (DBReport and DBLookup) with complex SQL queries or in scenarios where you need to simultaneously retrieve multiple rows. Instead, use the data services functionality of WSO2 Enterprise Integrator. For information on how to use the data services functionality, see the Tutorials .

  • Follow the guidelines described below if you want to use mediators in scenarios that require message transformation:
    • The most common message transformation use case is reconstructing the entire message payload according to the required format of the backend service. You can use the PayloadFactory Mediator  to do the transformation in this use case, if you know that the structure of the new payload is simple, which means the message format is fixed, and only a few parameters are extracted from the original message.
    • If the original message has repetitive segments and if you want to transform each of those segment into a new format with repetitive segments, you can use the For-Each Mediator together with the PayloadFactory mediator. The For-Each mediator iterates through the repetitive segments and the PayloadFactory mediator constructs the segments of the message to a new format. The combination of For-Each and PayloadFactory gives the functionality provided by the For-Each function in XSLT.
    • If only a small part of the message needs to be modified (e.g., you need to add/remove an element) you should use the Enrich Mediator.
    • If the transformation logic is complex (i.e., the logic includes repetitive segments, conditional transformations, etc), you can use the XSLT Mediator  to do the transformation.


      When you use the XSLT mediator, a third party engine does the message transformation. Therefore, this can impact the performance.

    • If you want to change the structure of the data in a message, or convert and transform one data format to another, use the Data Mapper Mediator.
    • If you want to work with large file transformations, use the Smooks Mediator.
  • Using $ctx instead of get-property():
    If you need to retrieve a property that you have set on a message, use the predefined XPath variables such as $ctx instead of the get-property() function for better performance. For example, use $ instead of get-property('').
    For more information on the predefined XPath variables that you can use to retrieve a property, and for examples of XPath variable usage, see Synapse XPath Variables.


    The use of the get-property() function can have a lower performance because it does a registry lookup when the value is not available in the message context. Therefore, the recommended approach is to use predefined XPath variables when you need to retrieve a property.

    You will encounter this performance issue only if you are using WSO2 ESB 4.9.0 or below.

  • Using  In and Out mediators
    A Proxy service or REST API resource has a InSequence to handle the request message flow, and has an OutSequence to handle the response message flow. Therefore, the In mediator and Out mediator should not be used in proxy services or REST API resources. However, you should use the In mediator and Out mediator in the main sequence.

  • Using the Loopback mediator
    Do not include the Loopback mediator in the OutSequence.


When a message passes from the InSequence (request path) to the OutSequence (response path), you cannot use the Loopback mediator to move the message back to the OutSequence again.

The following diagram illustrates a proxy/REST API with a Loopback mediator:

  • Reusing a defined sequence
    If you want to repeatedly use the same mediation sequence, you can define it and save it either in the Synapse configuration or in the Registry, with a unique name. Then you can call the mediation sequence from the main sequence as well as from multiple proxy services and REST APIs. The saved sequence can be called via the Sequence mediator or can be selected as the InSequence, OutSequence, or FaultSequence when you define a proxy service or a REST API.

    The following diagram illustrates how a saved sequence can be called using the Sequence mediator:


Working with proxy services

  • Use REST APIs instead of proxy services for RESTful service development.

Working with endpoints

  • Do not use anonymous endpoints. This is because in case there is an error in your sequence, having anonymous endpoints makes it difficult to identify the endpoint that is causing the error. Therefore, always use named endpoints.


    Anonymous endpoints are represented by a random auto generated name in the synapse configuration. Therefore, when an error occurs, it is difficult to identify the endpoint that is causing the error.

  • Configure timeout settings appropriately. 


    Timeout configurations are required before you go into production with the system.


The above diagram illustrates the typical message flow when a proxy service is involved in a client server communication. There are two connections involved in the scenario. They are Client to Proxy connection and Proxy to Backend connection. These two connections are two separate connections that do not depend on each other. Therefore, even if one of the connections timeout, it does not affect the other connection.

Following are the most important timeout parameters you should configure in your system before going into production:

ParameterDescriptionConfiguration FileDefault ValueRecommended Value
http.socket.timeoutSocket timeout of http connections.passthru-http.properties180000180000
Endpoint timeoutApplication level timeout.Endpoint configuration filessynapse.global_timeout_intervalDepends on the use case, Typically 120000
synapse.global_timeout_intervalGlobal timeout value for endpoints. Can be overwritten by individual endpoint timeout values.synapse.properties120000120000
synapse.timeout_handler_intervalDuration between two TimeoutHandler executions.synapse.properties1500015000

Let's have a look at the purpose of the above parameters in detail.

    • http.socket.timeout : This represents the socket timeout value of the Passthrough http/https transport sender and listener. You can find the file in the <EI_HOME>/conf directory.
    • Endpoint timeout: This is the timeout parameter that you should configure at the endpoint level. You can configure timeout values as required for specific endpoints.
      Following is a sample endpoint configuration that is configured with timeout parameters. Here, <duration> is the timeout value, and <responseAction> is the action to be taken on timeout. In this example the action to be taken on timeout is to invoke the FaultSequence.

   <address uri="http://localhost:8281/services/SimpleStockQuoteService">

Follow the formula Socket Timeout > max(Global endpoint timeout,Timeout of individual endpoints), and make sure that you set the  http.socket.timeout to a value higher than all other endpoint timeout values.

    • synapse.global_timeout_interval : Synapse, which is the underlying mediation engine of WSO2 Enterprise Integrator is a complete asynchronous messaging engine that does not block its worker threads on network I/O. Instead, it registers a call-back for a particular request and returns the threads without waiting for a response. When a response is available, the registered call-back is used to correlate it with the relevant request so that further processing can be done.
      If the backend server does not respond, it is required to clear the registered call-backs after a particular duration to prevent possible memory leaks. This duration is set via a timer task called TimeoutHandler. The synapse.global_timeout_interval parameter represents the duration that a call-back should be kept in the call-back store. 

      If you have configured a timeout value at the endpoint level, the global timeout value is not taken into consideration for that endpoint. For all the other endpoints, which do not have a timeout value configured, the global value is considered as the timeout value.

      You can configure the synapse.global_timeout_interval parameter in the <EI_HOME>/conf/ file. The default value is 120 seconds. If you want to support endpoint timeout values that are greater than 120 seconds, set the synapse.global_timeout_interval to a value more than 120 seconds. However, the need to set such large timeout values for endpoints is extremely unlikely.

    • synapse.timeout_handler_interval : The TimeoutHandler is executed every 15 seconds by default. Therefore, the time that call-backs get cleared can deviate up to 15 seconds from the configured value.
      You can configure the TimeoutHandler execution interval by specifying a required value for synapse.timeout_handler_interval in the <EI_HOME>/conf/ file.
  • Set the socket timeout value and individual endpoint timeout values appropriately.


    Use the following formula when you set timeout values:

    Socket Timeout > max(Global endpoint timeout, Timeout of individual endpoints)

  • Be sure to fine tune advanced configuration parameters.
    Although advanced configurations are optional, it is recommended to set proper values for the properties based on your use case. The happy path should work without a problem with the default settings, but you may encounter issues in production when the system does not follow the happy path. For example, If you use the default configurations, and as error occurs in your sequence, the endpoint would get suspended immediately and subsequent messages to that endpoint get rejected without being sent to the backend service. This might not be the expected behaviour in every use case. Therefore, it is important to perform endpoint error handling based on the use case.

  • Use the HTTP endpoint for RESTful service invocations. The HTTP endpoint is especially designed to make RESTful service integration easy. 
    For example, it supports url-templates, which is an option to set the http method.
  • For RESTful service integration, use either REST APIs or HTTP endpoints. You can use REST APIs to expose an integration solution as a RESTful service, and use HTTP endpoints to logically represent a RESTful backend service.

Error handling

Behaviour of the FaultSequence
  • If a sequence explicitly defines a fault handler using the onError attribute, WSO2 Enterprise Integrator invokes that specific onError sequence whenever an error occurs in the sequence. This is true even if the sequence is invoked by a proxy service or in an API.


  • If a request arrives via the main sequence and fails within a sequence that does not explicitly define a fault handler, the default FaultSequence  is invoked.
  • If a request arrives via a proxy service or an API, and fails within a sequence that does not explicitly define a fault handler, the FaultSequence of the proxy service is invoked.
  • If the proxy service does not have a FaultSequence defined, the default fault handler sequence is invoked.


    This is only applicable to WSO2 ESB 4.9.0 and above.

  • If there is a FaultSequence defined at the proxy service-level, and the onError sequence is referenced in the InSequence/OutSequence, then the onError sequence of the relevant InSequence/OutSequence is invoked in the event of an error. In this case the proxy service FaultSequence is ignored. For more information on how this works, see Specifying a Fault Sequence with a Regular Mediation Sequence
  • If you send a request to a REST API, and there is no matching resource defined in the API for the request (i.e., REST API resource mismatch), an HTTP status code 200 is returned. You should define a default error sequence called _resource_mismatch_handler_ to handle such requests. 
Best practices
  • Whenever an error occurs in WSO2 Enterprise Integrator, the mediation engine attempts to provide as much information as possible about the error. This is done by initializing a set of property values on the erroneous message. Following are the properties:
The above properties can be logged using the log mediator as follows inside a FaultSequence path.
<log level="custom">
	<property name="text" value="An unexpected error occurred"/>
	<property name="message" expression="$ctx:ERROR_MESSAGE"/>
	<property name="code" expression="$ctx:ERROR_CODE"/>
	<property name="detail" expression="$ctx:ERROR_DETAIL"/>
	<property name="exception" expression="$ctx:ERROR_EXCEPTION"/>

  • When you use the above properties, be sure to log the sequence name and proxy service/API name as well if you want to make debugging issues easier.
  • If the configuration is complex, you need to separate the configuration into multiple sequences. When the configuration is separated into multiple sequences, you need to define an error handler (onError sequence)  in each sequence.


For a complete guide on troubleshooting issues that you may come across when working with enterprise service bus capabilities, see the Enterprise Service Bus Troubleshoot Guide.


  • Define a test strategy to plan what should be tested in a specific project.
  • Create a test plan covering all functional scenarios and performance tests.
  • Write Jmeter, SoapUI test cases. If applicable always write automation tests.
  • Write java integration tests whenever applicable to automate the test scenarios.
  • Automate web application testing using Selenium.
  • If you have an integration solution, isolate test scenarios of each product as much as possible and test the scenarios as separate units. Then you can write integration tests for the integration scenarios including one or more products using java tools such as Jmeter and Soap UI.
  • For an application development project, you should perform tests throughout the Software Development Life Cycle (SDLC). Make sure that your testing environment is identical to the production environment when you execute test plans. (For example, resource allocation, VM sizes, VMs used for DBs, DB performance tuning, network resources etc in the production environment should be identical in the test environment)
  • Do not rely on test results of a single node test.
  • Test all custom solutions and artifacts that you develop. Never use default ports of the servers when testing custom features.
  • Before you move into production, run load tests on the development and test environments using samples that replicate the production use case.
  • Before you move into production, run a penetration test on the production setup. You need to suggest this to the customer and make arrangements for it beforehand.
  • Run a round of User Acceptance Tests (UAT) against the requirements to ensure that the system satisfies the customer's acceptance criteria. 
  • Document all functional test results and performance test results. Create a document explaining the steps followed, samples used, and the outcome of the tests for both functional test results as well as performance test results. Create a separate document including the summary of all the test results (e.g number of test cases that you executed, observations, summary etc). 
    Following is a sample template for functional test results:

    Test Case IDFunction
    Test Steps
    Expected Results
    Actual Results

    Following is a sample template for performance test results:

    Test Case IDFunction
    Test Steps
    Expected Results
    Actual Results
    CPU Usage
    Memory Usage
  • Never test on a single node.
  • Conduct proper developer tests.
  • Test use cases with all possible scenarios.
  • It is not sufficient to test only the happy path.
  • Do performance tests.


General guidelines

Recommended deployment patterns

Push model

  • All WSO2 Enterprise Integrator artifacts reside in a version control system such as SVN or Git.
  • The CI/CD server checks out the artifacts, builds and pushes the artifacts to individual WSO2 Enterprise Integrator nodes.


Sync model

Uses a file share or rsync to keep deployment artifacts in-sync across a set of nodes.

  • Linux file mount
    • All WSO2 Enterprise Integrator nodes mount the same remote file system as <EI_HOME>/repository/deployment/server directory.
    • If one node makes a change to that location by updating an artifact, the rest of the nodes see the change through remote mount and update the runtime.


  • rsync
    • One node acts as a master.
    • Artifact modification should be done only in the master node.
    • The master node runs rsync on a schedule(cron job) to copy <EI_HOME>/repository/deployment/server to remote nodes.


  • Hazelcast clustering
    • If a WSO2 Enterprise Integrator deployment requires task coordination/inbound endpoint coordination, hazelcast clustering should be enabled.


      Hazelcast is known to be unstable when the network is unreliable. Therefore, do not enable Hazelcast clustering unless coordination is required.

    • Hazelcast clustering can be enabled with any of the above deployment patterns.
    • When you use Hazelcast, it can result in cluster-wide failure if the inter-node communication is interrupted. To recover from such an issue, you have to restart the entire cluster at once. Round robin restart does not work in this situation. Be sure to keep customers informed of this limitation.
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