AWS Step Functions

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What is AWS Step Function?

There are many trends within the current cloud computing industry that have a sway on the conversations which take place throughout the market. One of these key areas of discussion is ‘Serverless’.

Serverless application deployment is a way of provisioning infrastructure in a managed way, without having to worry about any building and maintenance of servers – you launch the service and it works. Scaling, high availability, and automotive processes are looked after using managed AWS Serverless service. AWS Step Functions provides us a useful way to coordinate the components of distributed applications and microservices using visual workflows.

What is AWS Step Functions?

AWS Step Functions let developers build distributed applications, automate IT and business processes, and build data and machine learning pipelines by using AWS services. 

Using Step Functions workflows, developers can focus on higher-value business logic instead of worrying about failures, retries, parallelization, and service integrations. In other words, AWS Step Functions is serverless workload orchestration service which can make developers’ lives much easier.

Components and Integrations

AWS Step Functions consist of a few components, the first being a State Machine.

What is a state machine?

The State Machine model uses given states and transitions to complete the tasks at hand. It is an abstract machine (system) that can be in one state at a time, but it can also switch between them. As a result, it doesn’t allow infinity loops, which removes one source of errors entirely, which is often costly.

With AWS Step Functions, you can define workflows as state machines, which simplify complex code into easy-to-understand statements and diagrams. The process of building applications and confirming they work as expected is actually much faster and easier. 


In a state machine, a state is referred to by its name, which can be any string, but must be unique within the state machine. State instances exist until their execution is complete.

An individual component of your state machine can be in any of the following 8 types of states:

  • Task state – Do some work in your state machine. From a task state, Amazon Step Functions can call Lambda functions directly
  • Choice state – Make a choice between different branches of execution
  • Fail state – Stops execution and marks it as failure
  • Succeed state – Stops execution and marks it as a success
  • Pass state – Simply pass its input to its output or inject some fixed data
  • Wait state – Provide a delay for a certain amount of time or until a specified time/date
  • Parallel state – Begin parallel branches of execution
  • Map state – Adds a for-each loop condition


There are some limits which you need to be aware of when you are using AWS Step Functions. This table will break down the limits:

ResourceDefault quotaHard Limit
Maximum number of registered state machines10,00022,000 to 23,000
Maximum number of registered activities10,000Tens of thousands
Maximum request size1 MB per request. This is the total data size per Step Functions API request, including the request header and all other associated request data.N/A
Maximum open executions per account1,000,000 executions per AWS Region. Exceeding this will cause an ExecutionLimitExceeded error. Does not apply to Express Workflows.Millions
Synchronous Express Workflows concurrent executions1,000-3,700 (varies per region)Tens of thousands. The existing account capacity limits are not affected by Synchronous Express Workflows.

Use Cases and Examples

If you need to build workflows across multiple Amazon services, then AWS Step Functions are a great tool for you. Serverless microservices can be orchestrated with Step Functions, data pipelines can be built, and security incidents can be handled with Step Functions. It is possible to use Step Functions both synchronously and asynchronously.

Instead of manually orchestrating long-running, multiple ETL jobs or maintaining a separate application, Step Functions can ensure that these jobs are executed in order and complete successfully.

As a third feature, Step Functions are a great way to automate recurring tasks, such as updating patches, selecting infrastructure, and synchronizing data, and Step Functions will scale automatically, respond to timeouts, and retry missed tasks when they fail.

With Step Functions, you can create responsive serverless applications and microservices with multiple AWS Lambda functions without writing code for workflow logic, parallel processes, error handling, or timeouts.

Additionally, services and data can be orchestrated that run on Amazon EC2 instances, containers, or on-premises servers.


Each time you perform a step in your workflow, Step Functions counts a state transition. State transitions, including retries, are charged across all state machines.

There is a Free Tier for AWS Step Functions of 4000 State Transitions per month.

With AWS Step Functions, you pay for the number state transitions you use per month. 

Step Functions count a state transition each time a step of your workflow is executed. You are charged for the total number of state transitions across all your state machines, including retries.

State Transitions cost a flat rate of $0.000025 per state transition thereafter.


In summary, Step Functions are a powerful tool which you can use to improve the application development and productivity of your developers. By migrating your logic workflows into the cloud you will benefit from lower cost, rapid deployment. As this is a serverless service, you will be able to remove any undifferentiated heavy lifting from the application development process.

Interview Questions

Q: How does AWS Step Function create a State Machine?
A: A state machine is a collection of states which allows you to perform tasks in the form of lambda functions, or another service, in sequence, passing the output of one task to another. You can add branching logic based on the output of a task to determine the next state.

Q: How can we share data in AWS Step Functions without passing it between the steps?
A: You can make use of InputPath and ResultPath. In the ValidationWaiting step you can set the following properties (in State Machine definition)

This way you can send to external service only data that is actually needed by it and you won’t lose access to any data that was previously in the input.

Q: How can I diagnose an error or a failure within AWS Step Functions?
A: The following are some possible failure events that may occur

  1. State Machine Definition Issues.
  2. Task Failures due to exceptions thrown in a Lambda Function.
  3. Transient or Networking Issues.
  4. A task has surpassed its timeout threshold.
  5. Privileges are not set appropriately for a task to execute.

Ensure you explore each of these options thoroughly as these are the most likely solutions.

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