AWS Step Functions: Using Parallel State
Tags: devops, aws, programming, amazon
Published: 2024-01-04 14:46:45

Before diving into this post, I recommend you first check out: [Introduction to AWS Step Functions Using Terraform as an Infrastructure as Code Tool](https://dev.to/aws-builders/introduction-to-aws-step-functions-using-terraform-as-infrastructure-as-code-tool-33il)

---


The Parallel State type in AWS Step Functions is particularly relevant for scenarios where the simultaneous execution of various operations is required. This feature not only speeds up processes but also provides a flexible and scalable way to handle complex tasks. In this article, we will explain a basic example of Parallel State, providing a detailed guide on its configuration and use. Our goal is to offer a clear understanding of how to implement this powerful tool in your AWS workflows, fully leveraging its capabilities to optimize your cloud processes.

## Common Use Cases

1. **Parallel Data Processing**
   In situations where large volumes of data need to be processed, Parallel State allows for dividing the workload into multiple tasks that can be executed simultaneously. This is particularly useful in big data and data analysis applications, where processing and analyzing data from multiple sources at the same time is required.

2. **Microservices and Distributed Applications**
   In microservices-based architectures, different components of an application may need to perform tasks in parallel. Parallel State facilitates this coordination, allowing various services to function simultaneously to complete a larger process.

3. **Automation of Complex Workflows**
   In workflows that involve multiple steps or stages, such as in approval or review processes, Parallel State can be used to execute several steps in parallel, speeding up the overall process and improving operational efficiency.

4. **Simultaneous Testing and Analysis**
   In development and QA environments, Parallel State can be used to execute tests or analyses in parallel, reducing the total time needed for software validation or quality analysis.

5. **IT Operations and Infrastructure Management**
   For tasks such as infrastructure deployment, system updates, or security patches, Parallel State allows multiple operations to be carried out at the same time, resulting in faster and more efficient management of IT resources.

## Basic Example

```
{
  "Comment": "Ejemplo de Step Function con parallel state",
  "StartAt": "EstadoInicial",
  "States": {
    "EstadoInicial": {
      "Type": "Pass",
      "Result": {
        "mensajeInicial": "Inicio del flujo de trabajo"
      },
      "Next": "ProcesoParalelo"
    },
    "ProcesoParalelo": {
      "Type": "Parallel",
      "ResultPath": "$.resultadosParalelos",
      "Next": "EstadoFinal",
      "Branches": [
        {
          "StartAt": "Rama1",
          "States": {
            "Rama1": {
              "Type": "Pass",
              "Result": {
                "resultadoRama1": "Dato de la Rama 1"
              },
              "End": true
            }
          }
        },
        {
          "StartAt": "Rama2",
          "States": {
            "Rama2": {
              "Type": "Pass",
              "Result": {
                "resultadoRama2": "Dato de la Rama 2"
              },
              "End": true
            }
          }
        }
      ]
    },
    "EstadoFinal": {
      "Type": "Pass",
      "ResultPath": "$.resultadoFinal",
      "InputPath": "$.resultadosParalelos",
      "Result": {
        "mensajeFinal": "Fin del flujo de trabajo"
      },
      "End": true
    }
  }
}
```


![Graphical definition](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/933bvdw4x6m40psieqtw.png)

In this example, we present an AWS Step Function designed to demonstrate the use of a Parallel State. This workflow includes an initial state, a parallel state with two branches, and concludes with a state that converges the results of the parallel branches.

### Initial State

- **Type**: Pass. This type of state simply passes its input to its output without modification. Here, it is used to set an initial message, indicating the start of the workflow.
- **Result**: A JSON object with an initial message is assigned, for example, `{"initialMessage": "Start of the workflow"}`.

### Parallel Process

- **Type**: Parallel. This state allows the execution of multiple branches in parallel.
- **ResultPath**: `$.parallelResults`. This field specifies where the results of the parallel branches should be added in the input state of the next state. In this case, the results of both branches will be stored in an object called `parallelResults`.
- **Branches**: Contains two branches, each with its own Pass type state.
  - **Branch 1 and Branch 2**:
    - **Type**: Pass. Similar to the initial state, these states pass their input to their output. Here, each branch assigns a different result to a variable, such as `{"branch1Result": "Data from Branch 1"}` and `{"branch2Result": "Data from Branch 2"}`.

### Final State

- **Type**: Pass. This state marks the end of the workflow.
- **ResultPath**: `$.finalResult`. Indicates where the result of this state will be stored, in this case in `finalResult`.
- **InputPath**: `$.parallelResults`. Specifies that this state takes the results of the parallel state as input.
- **Result**: A JSON object with a final message is assigned, for example, `{"finalMessage": "End of the workflow"}`.

In this workflow, the Initial State marks the beginning and sets an initial message. Then, the Parallel Process executes two branches in parallel, each generating its own result. These results are combined and passed to the Final State, which receives them and sets a final message.

## Best Practices and Recommendations

When working with AWS Step Functions, and particularly with Parallel State, there are several best practices and recommendations that can help maximize the efficiency and effectiveness of your workflows:

### Careful Workflow Design
- **Advance Planning**: Carefully think about the structure of your workflow. Ensure that the use of Parallel States is truly beneficial and does not unnecessarily complicate the process.
- **Task Dependencies**: Avoid dependencies between tasks executed in parallel. The real value of a Parallel State lies in the ability to execute independent tasks simultaneously.

### Result Management
- **Result Consolidation**: Properly use the `ResultPath` field to consolidate the results of parallel tasks. Ensure that the results are combined in a way that is useful for subsequent steps.
- **Error Handling**: Design your workflow to properly handle errors in parallel tasks. Consider how a failure in one branch could affect the others and the workflow as a whole.

### Performance Optimization
- **Load Balancing**: Distribute the workload evenly among parallel tasks to avoid bottlenecks and maximize efficiency.
- **Scalability**: Consider the scalability of your workflow. Ensure that it can handle increases in load without degrading performance.

### Security and Access Control
- **Permissions and Roles**: Ensure that the functions and services used in your Step Function have the appropriate permissions, following the principle of least privilege.
- **Auditing and Monitoring**: Use monitoring tools and logs to audit the performance and activity of your workflows.

### Rigorous Testing
- **Comprehensive Testing**: Perform exhaustive testing of each component of the workflow, as well as the entire workflow, to ensure that everything works as expected, especially in failure scenarios.
- **Load Testing**: Test how your workflow behaves under different loads to identify potential performance or scalability issues.

### Documentation and Maintenance
- **Clear Documentation**: Maintain detailed documentation of your workflow and its configuration to facilitate maintenance and future updates.
- **Regular Updates**: Keep your workflow updated with the latest practices and features offered by AWS Step Functions.

In this [repository](https://github.com/jjoc007/poc_step_functions_examples/tree/main/5_parallel_state), you will find the example ready to deploy in Terraform. Feel free to download it and give it a try.

## References:

- **Example Repository**: [https://github.com/jjoc007/poc_step_functions_examples/tree/main/5_parallel_state](https://github.com/jjoc007/poc_step_functions_examples/tree/main/5_parallel_state)
- **Official Documentation**: [https://states-language.net/spec.html#parallel-state](https://states-language.net/spec.html#parallel-state)

## Related Content:

- [Introduction to AWS Step Functions](https://dev.to/aws-builders/introduction-to-aws-step-functions-using-terraform-as-infrastructure-as-code-tool-33il)
- [AWS Step Functions: Using the Wait State Type](https://dev.to/aws-builders/aws-step-functions-using-the-wait-state-type-1ab1)
- [AWS Step Functions: Sending an Email from a State](https://dev.to/aws-builders/aws-step-functions-sending-an-email-from-a-state-5b76)
- [AWS Step Functions: Example of an HTTP Request](https://dev.to/aws-builders/aws-step-functions-example-http-request-call-2h2b)

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