AWS Step Functions is a fully managed service that makes it easy to coordinate the components of distributed applications and microservices using visual workflows. Building applications from individual components that each perform a discrete function lets you scale easily and change applications quickly. Step Functions is a reliable way to coordinate components and step through the functions of your application. Step Functions provides a graphical console to arrange and visualize the components of your application as a series of steps. This makes it simple to build and run multi-step applications. Step Functions automatically triggers and tracks each step, and retries when there are errors, so your application executes in order and as expected. Step Functions logs the state of each step, so when things do go wrong, you can diagnose and debug problems quickly. You can change and add steps without even writing code, so you can easily evolve your application and innovate faster.
Breaking an application into service components (or steps) ensures that the failure of one component does not bring the whole system down, that each component scales independently, and that components may be updated without requiring the entire system to be redeployed after each change. The coordination of service components involves managing execution dependencies, scheduling, and concurrency in accordance with the logical flow of the application. In such an application, developers may use service orchestration to do this and to handle failures.
AWS Step Functions helps with any computational problem or business process that can be subdivided into a series of steps. It’s also useful for creating end-to-end workflows to manage jobs with interdependencies. Common use cases include:
Data processing: consolidate data from multiple databases into unified reports, refine and reduce large data sets into useful formats, or coordinate multi-step analytics and machine learning workflows
DevOps and IT automation: build tools for continuous integration and continuous deployment, or create event-driven applications that automatically respond to changes in infrastructure
E-commerce: automate mission-critical business processes, such as order fulfillment and inventory tracking
Web applications: implement robust user registration processes and sign-on authentication
Using AWS Step Functions, you define state machines that describe your workflow as a series of steps, their relationships, and their inputs and outputs. State machines contain a number of states, each of which represents an individual step in a workflow diagram. States can perform work, make choices, pass parameters, initiate parallel execution, manage timeouts, or terminate your workflow with a success or failure. The visual console automatically graphs each state in the order of execution, making it easy to design multi-step applications. The console highlights the real-time status of each step and provides a detailed history of every execution. For more information, see How Step Functions Works in the AWS Step Functions Developer Guide.
You can configure your state machines to perform work by using activity tasks and service tasks. Activity tasks let you assign a specific step in your workflow to code running somewhere else (known as an activity worker). An activity worker can be any application that can make an HTTP connection, hosted anywhere. For example, activity workers can run on an Amazon EC2 instance, on a mobile device, or on an on-premises server. The activity worker polls Step Functions for work, takes any inputs from Step Functions, performs the work using your code, and returns results. Since activity workers request work, it is easy to use workers that are deployed behind a firewall.
Service tasks let you connect a step in your workflow to a supported AWS service. Step Functions pushes requests to other services so they can perform actions for your workflow, waits for the service task to complete, and then continues to the next step.
An AWS Step Functions state machine can contain combinations of activity tasks and service tasks. AWS Step Functions applications can also combine activity workers running in a data center with service tasks that run in the cloud. The workers in the data center continue to run as usual, along with any cloud-based service tasks.
You should consider AWS Step Functions when you need to coordinate service components in the development of highly scalable and auditable applications. You should consider using Amazon Simple Queue Service (Amazon SQS), when you need a reliable, highly scalable, hosted queue for sending, storing, and receiving messages between services. Step Functions keeps track of all tasks and events in an application. Amazon SQS requires you to implement your own application-level tracking, especially if your application uses multiple queues. The Step Functions Console and visibility APIs provide an application-centric view that lets you search for executions, drill down into an execution’s details, and administer executions. Amazon SQS requires implementing such additional functionality. Step Functions offers several features that facilitate application development, such as passing data between tasks and flexibility in distributing tasks. Amazon SQS requires you to implement some application-level functionality. While you can use Amazon SQS to build basic workflows to coordinate your distributed application, you can get this facility out-of-the-box with Step Functions, alongside other application-level capabilities.
You should consider using AWS Step Functions for all your new applications, since it provides a more productive and agile approach to coordinating application components using visual workflows. If you require external signals to intervene in your processes, or you would like to launch child processes that return a result to a parent, then you should consider Amazon Simple Workflow Service (Amazon SWF). With Amazon SWF, instead of writing state machines in declarative JSON, you write a decider program to separate activity steps from decision steps. This provides you complete control over your orchestration logic, but increases the complexity of developing applications. You may write decider programs in the programming language of your choice, or you may use the Flow framework to use programming constructs that structure asynchronous interactions for you.
Workflows that you create with AWS Step Functions can connect and coordinate other AWS services using service tasks. For example, you can:
Invoke an AWS Lambda function
Run an Amazon Elastic Container Service or AWS Fargate task
Get an existing item from an Amazon DynamoDB table or put a new item into a DynamoDB table
Submit an AWS Batch job and wait for it to complete
Publish a message to an Amazon SNS topic
Send a message to an Amazon SQS queue
Start an AWS Glue job run
Create an Amazon SageMaker job to train a machine learning model or batch transform a data set
To learn more about using Step Functions to connect to other AWS services, see the Step Functions Developer Guide. You can also create tasks in your state machines that run applications, see the FAQ in the Overview section, How does AWS Step Functions connect to my resources?
You can associate your Step Functions APIs with Amazon API Gateway so that these APIs invoke your state machines when an HTTPS request is sent to an API method that you define. You can use an Amazon API Gateway API to start Step Functions state machines that coordinate the components of a distributed backend application, and integrate human activity tasks into the steps of your application such as approval requests and responses. You can also make serverless asynchronous calls to the APIs of services that your application uses. For more information, try our tutorial, Creating a Step Functions API Using API Gateway.
AWS Step Functions sends metrics to Amazon CloudWatch and AWS CloudTrail for application monitoring. Amazon CloudWatch collects and track metrics, sets alarms, and automatically reacts to changes in AWS Step Functions. AWS CloudTrail captures all API calls for Step Functions as events, including calls from the Step Functions console and from code calls to the Step Functions APIs. Step Functions also supports Amazon CloudWatch Events managed rules for each integrated service in your workflow, and will create and manage CloudWatch Events rules in your AWS account as needed. For more information, see Monitoring and Logging in the AWS Step Functions Developer Guide.
AWS Step Functions is integrated with AWS Identity and Access Management (AWS IAM). IAM policies can be used to control access to the Step Functions APIs, and when you create a state machine in the AWS Step Functions console, Step Functions will recommend an IAM policy based on the resources used in your state machine definition. For more information, see IAM Policies for Connected Services in the AWS Step Functions Developer Guide.