49 lines
1.7 KiB
Markdown
49 lines
1.7 KiB
Markdown
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---
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tags: [AWS]
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---
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# AWS Step functions and state machines
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_AWS Step Functions_ is an AWS service that allows you to coordinate distributed
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applications and microservices by creating workflows.
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Workflows are made up of a series of steps and are known as **state machines**.
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A state machine defines:
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- the states of the workflow
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- the transitions between states
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- the inputs and outputs of each state
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State machines are defined via a JSON object which specifies the states and the
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transitions between them. It also includes error catchers and retry logic.
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At the beginning you define a `StartAt` state which is the entrypoint of the
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state machine. This can be manually triggered, or more likely, triggered by
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another AWS service such as a
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[Lambda](Lambda_programming_model.md), an
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[API Gateway](AWS_API_Gateway.md) request or a messaging/queue
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event.
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The state machine ultimately ends at an end state. In between are various
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intermediary states which can include:
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- Task states (do something)
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- Choice states (do something based on conditions)
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- Wait states
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- Success states (if preceding state succeeds do X)
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- Fail states (if preceding state fails do Y)
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- Parallel states
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The diagram below shows the definition of a given state machine. On the left is
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the JSON specification. On the right is a diagramatic representation that shows
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the control flow and all possible steps that comprise a given pathway / state:
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For each execution of the state machine (each time it is triggered) you can
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review the runtime. The flow diagram will highlight green to show the given
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pathway, and you can also see the inputs and outputs for each step and any
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errors:
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