AWS Step Functions
Developer Guide

State Machine Structure

State machines are defined using JSON text that represents a structure containing the following fields:

Comment (Optional)

A human-readable description of the state machine.

StartAt (Required)

A string that must exactly match (case-sensitive) the name of one of the state objects.

TimeoutSeconds (Optional)

The maximum number of seconds an execution of the state machine may run; if it runs longer than the specified time, then the execution fails with an States.Timeout Error name.

Version (Optional)

The version of Amazon States Language used in the state machine, default is "1.0".

States (Required)

This field's value is an object containing a comma-delimited set of states.

The States field contains a number of States:

{ "State1" : { }, "State2" : { }, ... }

A state machine is defined by the states it contains and the relationships between them.

Here's an example:

{ "Comment": "A Hello World example of the Amazon States Language using a Pass state", "StartAt": "HelloWorld", "States": { "HelloWorld": { "Type": "Pass", "Result": "Hello World!", "End": true } } }

When an execution of this state machine is launched, the system begins with the state referenced in the StartAt field ("HelloWorld"). If this state has an "End": true field, the execution stops and returns a result. Otherwise, the system looks for a "Next": field and continues with that state next. This process repeats until the system reaches a terminal state (a state with "Type": "Succeed", "Type": "Fail", or "End": true), or a runtime error occurs.

The following rules apply to states within a state machine:

  • States can occur in any order within the enclosing block, but the order in which they're listed doesn't affect the order in which they're run, which is determined by the contents of the states themselves.

  • Within a state machine, there can be only one state that's designated as the start state, designated by the value of the StartAt field in the top-level structure. This state is the one that is executed first when the execution starts.

  • Any state for which the End field is true is considered to be an end (or terminal) state. Depending on your state machine logic—for example, if your state machine has multiple branches of execution—you may have more than one end state.

  • If your state machine consists of only one state, it can be both the start state and the end state.