Introduction
AWS Step Functions offers two workflow types, named Standard and Express. Both are defined in the same way, as a state machine written in the Amazon States Language, but they differ in duration, pricing, execution guarantees, and history. A workflow type determines how an execution is run and billed. This guide compares the two types and explains when each should be chosen. Readers who are new to the service should first read the guide on what AWS Step Functions is.
What is being compared?
A Standard workflow is designed for processes that are long-running, that must be recorded in full, and that must be performed exactly once. An Express workflow is designed for processes that occur at very high volume and complete quickly. The definition of the state machine can be identical in both cases, so the choice is a matter of the operational characteristics rather than of the workflow logic.
Why the choice matters
The type that is selected affects how long an execution may run, how much it costs, whether a step might be repeated, and whether a full history is retained. A workload that is chosen incorrectly may become expensive, may fail to complete within the allowed time, or may lack the audit record that is required. The selection is therefore an important decision.
How each type works
A Standard workflow may run for up to one year and provides exactly-once execution, which means that each step is performed a single time. It is charged per state transition, which is each movement from one state to the next, and it records a durable history of every execution.
An Express workflow may run for up to five minutes and provides at-least-once execution, which means that a step may occasionally be performed more than once. Its tasks should therefore be idempotent, which means that repeating an operation produces the same result. It is charged by the number of executions, their duration, and the memory that is used, and its detail is sent to Amazon CloudWatch Logs when logging is enabled.
Comparison diagram
Where Standard is stronger
- Long duration. Executions may run for up to one year.
- Exactly-once execution. Each step is performed a single time.
- Full history. A durable record supports auditing and debugging.
- Human approval. An execution can wait for an external decision over a long period.
Where Express is stronger
- High volume. Very large numbers of executions can be run efficiently.
- Lower cost at scale. The per-execution model is often cheaper for short, frequent work.
- Low overhead. Short workflows complete quickly with minimal coordination cost.
When to choose each
- Standard suits order processing, human approval, and any process that must be auditable or long-running.
- Express suits high-volume event processing, data transformation, and short backend tasks.
- A Standard workflow can start an Express workflow as one of its steps, which combines the strengths of both.
Best practices
- The expected duration, volume, and auditing needs should be assessed before a type is chosen.
- Tasks in an Express workflow should be made idempotent, because a step may be performed more than once.
- Logging to Amazon CloudWatch should be enabled for Express workflows so that behavior can be observed.
- A high-volume section of a long process should be placed in an Express workflow that is started by a Standard workflow.
Common mistakes
- An Express workflow is chosen for work that must be recorded in full, which loses the durable history.
- A Standard workflow is chosen for very high-volume short work, which increases cost through per-transition charges.
- Idempotency is not implemented in an Express workflow, so a repeated step causes a duplicated effect.
- The five-minute limit of an Express workflow is exceeded, which causes the execution to fail.
Related AWS services
- AWS Lambda performs the work of most steps in either workflow type.
- Amazon CloudWatch receives the logs of Express workflows.
- Amazon EventBridge can start a workflow in response to an event.
Frequently Asked Questions
- What is the maximum duration of each workflow type?
- A Standard workflow may run for up to one year. An Express workflow may run for up to five minutes. Work that must run for a long time should use a Standard workflow.
- How are Standard and Express workflows priced?
- A Standard workflow is charged per state transition. An Express workflow is charged by the number of executions, their duration, and the memory used. For very high volume, the Express model is often less expensive.
- What execution guarantees does each type provide?
- A Standard workflow provides exactly-once execution. An Express workflow provides at-least-once execution, so its tasks should be idempotent.
- Does each type record execution history?
- A Standard workflow records a full, durable history. An Express workflow sends its detail to Amazon CloudWatch Logs when logging is enabled.
- Can the two types be combined?
- Yes. A Standard workflow can start an Express workflow as one of its steps, which allows a long, auditable process to contain a section of high-volume work.
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