Interview Questions 2 – Mulesoft / Mule ESB Tutorial

MuleSoft or Mule ESB interview Questions

Here are the most important and common mulesoft or mule esb interview questions and answers which are bound to be asked in any Mule ESB interview. Also see Mule Interview Questions I.

Inbound properties are immutable, are automatically generated by the message source and cannot be set or manipulated by the user.  They contain metadata specific to the message source. A message retains its inbound properties only for the duration of the flow; when a message passes out of a flow, its inbound properties do not follow it.

Outbound properties are mutable; can be set/modified in a flow and can become inbound properties when the message passes from the outbound endpoint of one flow to the inbound endpoint of a different flow via a transport. They contain metadata similar to that of an inbound property, but an outbound property is applied after the message enters the flow. Note that if the message is passed to a new flow via a flow-ref rather than a connector, the outbound properties remain outbound properties rather than being converted to inbound properties

SOAP Kit Router is used when a SOAP service is to be developed via WSDL. SOAP Kit Router will read the WSDL configured, validate the request message coming in (if configured) and send it to the appropriate flow for processing based on the operations been configured in WSDL.

API Kit Router is used when a REST base service is been created developed via RAML. API Kit Router will read the RAML configured, validate the request message coming in (if configured) and send it to the appropriate flow for processing based of the HTTP methods in RAML.

We can set variables using Variable component in mule, but variables component will set only 1 variable at a time. There are couple of ways to set multiple variables concurrently –

“Message Properties” Component –
In “Message Properties” will configure Scope to “invocation” and add variable name and its value in “Add message property”.

<message-properties-transformer scope="invocation" doc:name="Message Properties">
<add-message-property key="a" value="a"/>
<add-message-property key="b" value="b"/>
<add-message-property key="c" value="c"/>
</message-properties-transformer>

“Expression” Component –

<expression-component doc:name="Expression">
<![CDATA[
flowVars.a = 'a';
flowVars.b = 'b';
flowVars.c = 'c';]]>
</expression-component>

Parallel activate/flows can be executed in mule by using Scatter-Gather flow control component.
The routing message processor Scatter-Gather sends a request message to multiple targets concurrently. It collects the responses from all routes, and aggregates them into a single message.

The until-successful scope processes messages through the processors within its scope until the operation succeeds. Until-successful’s processing occurs asynchronously from the main flow. After passing a message into the until-successful scope, the main flow immediately regains control of the thread.

The Round Robin router iterates through a list of two or more routes in order, but it only routes to one of the routes each time it is executed. It keeps track of the previously selected route and never selects the same route consecutively. For example, the first time Round Robin executes, it selects the first route. The next time, it selects the second route. If the previously selected route is the last route in the list, Round Robin jumps to the first route.

The First Successful router iterates through its list of child routes, each containing a set of components, until the first successful execution. If none succeed, an exception is thrown.