Overview

Step Functions is a serverless orchestration service that lets you combine AWS Lambda functions and other AWS services to build business-critical applications.
Step Functions is based on state machines and tasks.
A state machine is a workflow.
A task is a state in a workflow that represents a single unit of work that another AWS service performs.
Each step in a workflow is a state.

Use cases

Data processing
- Step Functions provides the scalability, reliability, and availability needed to successfully manage your data processing workflows.
- You can manage millions of concurrent executions with Step Functions as it scales horizontally and provides fault-tolerant workflows.
- Process data faster using parallel executions like Step Functions’ Parallel state type, or dynamic parallelism using its Map state type.
- Examples of the types of data processing workflows that customers use Step Functions to accomplish include:
  - File, video, and image processing
  - Coordinate extract, transform and load (ETL) jobs
  - Batch processing and High Performance Computing (HPC) workloads
Machine learning
- Machine learning enables organizations to quickly analyze collected data to identify patterns, then make decisions with minimal human intervention.

When you create a state machine, you can select a Type of either Standard (default) or Express.
The Type you choose cannot be changed after your state machine has been created.
Standard Workflows are ideal for long-running, durable, and auditable workflows. They can run for up to a year and you can retrieve the full execution history using the Step Functions API, up to 90 days after your execution completes.
- Exactly-once workflow execution
Express Workflows are ideal for high-volume, event-processing workloads such as IoT data ingestion, streaming data processing and transformation, and mobile application backends.
- They can run for up to five minutes.
- Express Workflows employ an at-least-once model, where there is a possibility that an execution might be run more than once.
- Asynchronous Express Workflows return confirmation that the workflow was started, but do not wait for the workflow to complete.
  - At-least-once workflow execution
- Synchronous Express Workflows start a workflow, wait until it completes, then return the result.
  - At-most-once workflow execution

Individual states can make decisions based on their input, perform actions, and pass output to other states.
A state is referred to by its name, which can be any string, but which must be unique within the scope of the entire state machine.
States can perform a variety of functions in your state machine:
- Do some work in your state machine (a Task state)
- Make a choice between branches of execution (a Choice state)
- Stop an execution with a failure or success (a Fail or Succeed state)
- Simply pass its input to its output or inject some fixed data (a Pass state)
- Provide a delay for a certain amount of time or until a specified time/date (a Wait state)
- Begin parallel branches of execution (a Parallel state)
- Dynamically iterate steps (a Map state)

What is AWS Step Functions? - AWS Step Functions