What is the difference between using private flow

1. What is the difference between
using private flow versus VM
transport?

2. • In this post, I will show the differences between chaining flows with
VM transport versus chaining flows with flow reference. When I need
to divide my Mule flows into reusable units, I often break them into
smaller flows and then chain them together in a main flow.
• Flows can be chained together using flow-refs or using VM
connectors; most recent examples use the flow-refs. However, flow-
refs are a Mule 3 addition and in Mule 2 VM connectors were used to
chain flows.

3. • Given this background and with flow-refs being more of the
recommended approach, is there a scenario when we would want to
use VM connectors? Yes, there is! But the majority of the time flow-
refs are preferred over the VM transport and here is why.
• * VM connector creates a transport barrier in the flow: In a transport
barrier, your Mule message goes through an entire serialization and
deserialization process which results in a new Mule message with the
same payload. Read about the effect of transport barrier on a mule
message here.

4. When one would prefer to use a VM
transport over a flow reference
• One case would be that VM endpoints enable message redelivery
strategies to be configured in your exception handling blocks – this is
not possible with flow-refs. VMs can do this because they internally
use a queue to hold messages while flow-refs are similar to simple
method calls.

5. • Look at the sample flow below; here the message will be redelivered
five times and is enabled by the use of VM inbound

6. • Contrast that to a private flow and chaining with flow-refs, if an
exception occurs in the called flow even though we have a rollback
strategy configured it will NOT execute because there is no internal
queue involved.

8. • To summarize, don’t hesitate to use VM transports if you need
redelivery of messages. There are also differences in the use of thread
pools between private flows and VMs, but I will leave that for another
post. The sample source code for this post is available on Github.
• If you want to learn more about Mule ESB, Mule ESB is a great
platform for developers to connect applications together quickly and
easily. Feel free to try Anypoint Platform for 30 days