MuleESB / Apache Camel Interview Questions

What is the Multicast EIP and how does it differ from Recipient List?

The Multicast EIP sends a copy of the current message to a fixed, statically defined list of endpoints. It is declared at route build time. Recipient List, by contrast, resolves the destination list dynamically from the message at runtime. Use Multicast when you always fan out to the same set of endpoints regardless of message content.

// Multicast to two fixed endpoints (sequential by default):
from("direct:order")
    .multicast()
        .to("jms:queue:billing", "jms:queue:shipping", "jms:queue:analytics")
    .end();

// Parallel processing with aggregation:
from("direct:enrich")
    .multicast(new MergeStrategy())
        .parallelProcessing()
        .to("direct:getCreditScore", "direct:getAddress", "direct:getHistory")
    .end();

Multicast vs Recipient List
Aspect	Multicast	Recipient List
Destination list	Fixed at build time in the route definition	Computed from message header/expression at runtime
Typical use	Always fan out to the same set	Subscription-based or tenant-aware routing
Parallelism	Optional via parallelProcessing()	Optional via parallelProcessing()
Aggregation	Optional AggregationStrategy	Optional AggregationStrategy

Which statement correctly distinguishes Multicast from Recipient List? Multicast is always sequential; Recipient List is always parallel

✗ Try again — both support optional parallelProcessing().

Multicast uses a static list of endpoints; Recipient List resolves destinations dynamically

✓ Well done! Multicast destinations are fixed in the route; Recipient List computes them from the Exchange.

Multicast aggregates responses; Recipient List discards them

✗ Try again — both can use an optional AggregationStrategy.

When using Multicast with parallelProcessing() and an AggregationStrategy, what does the strategy do? It decides which thread each endpoint runs on

✗ Try again — thread management is handled by the Camel thread pool.

It merges the responses from all recipient endpoints into a single Exchange

✓ Well done! The AggregationStrategy combines replies from each branch back into one outgoing Exchange.

It filters out failed endpoint responses

✗ Try again — error handling is separate from aggregation.

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More Related questions...

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MuleESB / Apache Camel Interview Questions

What is the Multicast EIP and how does it differ from Recipient List?

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