* Clustering is a group of servers or mule runtime which acts as a single unit.
* Mulesoft Enterprise Edition supports scalable clustering to provide high availability for the Mulesoft application.
* In simple terms, virtual servers composed of multiple nodes and they communicate and share information through a distributed shared memory grid.
* By default, Mulesoft ensures the High availability of applications if clustering implemented.
* Let's consider the scenario one of the nodes in cluster crashed or goes down and under maintenance. In such cases, Mulesoft will ensure that requests are processed by other nodes in the cluster. Mulesoft clustering also ensures that the request is load balanced between all the nodes in a cluster.
* Clustering is only supported by on-premise Mule runtime and it is not supported in Cloudhub.
Correct answer is External monitoring tools or log aggregators must be configured to recognize the new nodes
* Rest of the options are automatically taken care of when a new node is added in cluster.
Reference:

If the size of the stream exceeds the maximum, a STREAM_MAXIMUM_SIZE_EXCEEDED error is raised.

Correct answer is EACH item VM message is processed AT LEAST ONCE by ONE ARBITRARY CloudHub worker. Each of the four CloudHub workers can be expected to process some item VM messages In Cloudhub, each persistent VM queue is listened on by every CloudHub worker - But each message is read and processed at least once by only one CloudHub worker and the duplicate processing is possible - If the CloudHub worker fails , the message can be read by another worker to prevent loss of messages and this can lead to duplicate processing - By default , every CloudHub worker's VM Listener receives different messages from VM Queue Referenece: https://dzone.com/articles/deploying-mulesoft-application-on-1-worker-vs-mult

Correct answer is Application A accesses the persistent object store via the Object Store REST API Application B uses the Object Store connector to access a persistent object * Object Store v2 lets CloudHub applications store data and states across batch processes, Mule components and applications, from within an application or by using the Object Store REST API. * On-premise Mule applications cannot use Object Store v2. * You can select Object Store v2 as the implementation for Mule 3 and Mule 4 in CloudHub by checking the Object Store V2 checkbox in Runtime Manager at deployment time. * CloudHub Mule applications can use Object Store connector to write to the object store * The only way on-premises Mule applications can access Object Store v2 is via the Object Store REST API. * You can configure a Mule app to use the Object Store REST API to store and retrieve values from an object store in another Mule app.

* Option A says "Perform EACH DB insert in a SEPARATE DB transaction". In this case if first DB insert is successful and second one fails then first insert won't be rolled back causing inconsistency. This option is ruled out.
* Option D says Perform BOTH DB inserts in ONE DB transaction.
Rule of thumb is when one or more DB connections are required we must use XA transaction as local transactions support only one resource. So this option is also ruled out.
* Option B acknowledges the before DB processing, so message is removed from the queue. In case of system failure at later point, message can't be retrieved.
* Option C is Valid: Though it says "do not ack JMS message", message will be auto acknowledged at the end of transaction. Here is how we can ensure all components are part of XA transaction: https://docs.mulesoft.com/jms-connector/1.7/jms-transactions Additional Information about transactions:
* XA Transactions - You can use an XA transaction to group together a series of operations from multiple transactional resources, such as JMS, VM or JDBC resources, into a single, very reliable, global transaction.
* The XA (eXtended Architecture) standard is an X/Open group standard which specifies the interface between a global transaction manager and local transactional resource managers.
The XA protocol defines a 2-phase commit protocol which can be used to more reliably coordinate and sequence a series of "all or nothing" operations across multiple servers, even servers of different types
* Use JMS ack if
- Acknowledgment should occur eventually, perhaps asynchronously
- The performance of the message receipt is paramount
- The message processing is idempotent
- For the choreography portion of the SAGA pattern
* Use JMS transactions
- For all other times in the integration you want to perform an atomic unit of work
- When the unit of work comprises more than the receipt of a single message
- To simply and unify the programming model (begin/commit/rollback)