Creating and using a subworkflow

You can use subworkflows to define a piece of logic or a set of steps you want to call multiple times, simplifying the workflow definition. Subworkflows are similar to a function or routine in a programming language. They can accept parameters and return values, allowing you to create more complex workflows with a broader range of applications.

This page covers defining a subworkflow and calling it from within a workflow. For information on basic workflow tasks, see Creating and updating an existing workflow and Executing a workflow.

Creating a workflow that uses a subworkflow

To create a subworkflow:

Add a main block to the top of the workflow definition:
```
main:
   steps:
       - step_name:
           ...
       ...
```
If a workflow has a subworkflow, the main workflow must be placed in a main block.
Define the subworkflow below the main steps of the workflow:
```
main:
   steps:
       - step_name:
           ...
       ...
[SUBWORKFLOW_NAME]:
    params: [PARAMETER_1[: DEFAULT_VALUE1], PARAMETER_2[: DEFAULT_VALUE2]...]
    steps:
        - step_name:
        ...
```
Replace the following:
- SUBWORKFLOW_NAME: Required. Name of the subworkflow.
- [PARAMETER_1, PARAMETER_2]: Optional. Parameters used by the subworkflow.
- DEFAULT_VALUE1, DEFAULT_VALUE2: Optional. Default values for the respective parameters.
If you don't need to pass parameters to the subworkflow, delete the params block. Note that any parameters must be enclosed in square brackets; for example: params: [first_name, last_name, country: "England"].
Within the subworkflow, define the steps just as you would in the main workflow.
To call the subworkflow from the main workflow, add a call section within a step in the main workflow, optionally supplying arguments to pass to the subworkflow:
```
main:
   - [STEP_NAME]:
       call: [SUBWORKFLOW_NAME]
       [args:
           ARG_1: VALUE
           ARG_2: VALUE
           ...]
       [result: OUTPUT_VARIABLE]
[SUBWORKFLOW_NAME]:
    params: [PARAMETER_1,PARAMETER_2...]
    steps:
        - step_1:
        ...
```
Replace the following:
- SUBWORKFLOW_NAME: Required. Name of the subworkflow.
- ARG_1, ARG_2: Optional. The arguments passed to the subworkflow, if the subworkflow accepts parameters.
- VALUE: Optional. The values the arguments are set to.
- OUTPUT_VARIABLE: Optional. The variable where the workflow stores the data the subworkflow returns, if the subworkflow returns anything.

Example

This example demonstrates defining a subworkflow named name_message and calling it from the main workflow:

main:
    steps:
        - call_subworkflow:
            call: name_message
            args:
                first_name: "Sherlock"
                last_name: "Holmes"
            result: output
        - call_subworkflow2:
            call: name_message
            args:
                first_name: "Ada"
                last_name: "Lovelace"
            result: output2
        - return_message:
            return: ${output + output2}

name_message:
    params: [first_name, last_name, country: "England"]
    steps:
        - prepareMessage:
            return: ${"Hello " + first_name + " " + last_name + " from " + country + "."}

This workflow definition does the following:

The main workflow calls the name_message subworkflow twice, from the steps call_subworkflow and call_subworkflow2.
The two steps supply different inputs for the arguments first_name and last_name, which are then passed to the subworkflow.
The subworkflow name_message takes the arguments passed to it and constructs a simple message, supplying the default value of England for the country variable.
The subworkflow returns the message it constructs to the main workflow.
The steps in the main workflow store the results as output and output2, respectively.
The main workflow combines output and output2 into a single message and returns the result: Hello Sherlock Holmes from England. Hello Ada Lovelace from England.

Creating and using a subworkflow

Creating a workflow that uses a subworkflow

Example

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