Why Upgrade from Mule 3 to Mule 4?

Intersmart solution
2 min readDec 27, 2021


The mule runtime engine is a lightweight integration engine, to put it simply. Mule allows you to install Mule apps, support domains, publish APIs through Exchange, get the client ID and secret, and apply rules to the API. Mule apps may be deployed on-premises or in the cloud using the Mule runtime engine. Several mule programs can run on a single mule runtime. Mule’s runtime engine is a global connectivity building component. By merging data and application integration across legacy systems, SaaS apps, and APIs, it links to applications, data, and devices.

Mule 4 is the latest version of Mule and was released on September 29, 2017.

Upgrading from Mule 3 to Mule 4

Why Upgrade from Mule 3 to Mule 4? MMA (Mule Migration Assistant), an open-source community tool, can help us move from Mule 3 to Mule 4.

Mule 3 application inventories are divided into three groups during migration.

Simple Application:

  1. Mule 3 programs that are simple can simply be converted to Mule 4.
  2. There are no custom components: There is no connection compatibility with the Dataweave transformation.

Medium Complexity:

  1. An application requiring re-architecture and the addition of new functionality.
  2. MEL expression is used often, with batch scope, record variables, and watermarks being used infrequently.

High Complexity:

  1. Complex applications with many processes, interfaces, and bespoke code must be verified.
  2. Dataweave and bespoke object storage are heavily used.

Some connections and syntaxes may not be moved after migrating through MMA. In these circumstances, a manual migration technique must be used.

In Mule 3, for example, the listener and HTTP request connectors are combined into a single connection. Listener and HTTP requests are two independent connections in Mule 4.

Mule 3 and 4 Differentiators

Reduced Development Time: Mule 4 allows us to design and deliver apps more quickly and easily than Mule 3. Mule 3 has four phases in a Batch work, whereas Mule 4 has three phases. Mule 4 does not have an input phase. The flow’s payload is passed to the batch.

Record variables are available in Mule 3. Unlike flow variables, these variables only exist during the process phase. Flow variables in Mule 4 operate exactly as well as record variables during batch processing, eliminating the requirement for record variables.

Simple and Intuitive: Mule 4 contains a lot of innovative and easy-to-use low-code capabilities.

Speed of Delivery: Mule 4 has streamlined development languages and a speedier onboarding process.

Actionable Visibility: In comparison to Mule 3, Mule 4 handles errors more proactively and has a simpler runtime setup. Mule 3 error handling is a framework with integrated and customizable error handling methods, whereas Mule 4 error handling is a framework with integrated and adjustable error handling mechanisms. Mule 4 includes a more integrated processing flow that is better able to deal with faults.

Future Proof Architecture: Mule 4 is scalable and extensible, with an improved self-tuning runtime.

Intentional Self-service: Mule 4 provides a more user-friendly upgrading route as well as centralized cooperation.



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