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AWS Step Functions
Developer Guide

Transitions

When an execution of a state machine is launched, the system begins with the state referenced in the top-level StartAt field. This field (a string) must exactly match, including case, the name of one of the states.

After executing a state, AWS Step Functions uses the value of the Next field to determine the next state to advance to.

Next fields also specify state names as strings, and must match the name of a state specified in the state machine description exactly (case-sensitive).

For example, the following state includes a transition to NextState:

"SomeState" : {
  ...,
  "Next" : "NextState"
}

Most states permit only a single transition rule via the Next field. However, certain flow-control states (for example, a Choice state) allow you to specify multiple transition rules, each with its own Next field. The Amazon States Language provides details about each of the state types you can specify, including information about how to specify transitions.

States can have multiple incoming transitions from other states.

The process repeats until it 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 designated as the start state, which is designated by the value of the StartAt field in the top-level structure.

  • 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.