Building a weather monitor with AWS SAM and Terraform — part 2
Source code can be found here
This article is the “state machine” part of the weather monitor. It is comprised of Step Functions and DynamoDB. Step Functions subscribes the weather data event from Event Bridge, and then insert the data into DynamoDB.
Step Functions
This part says Step Functions subscribes the demo.event (I haven't got time to update this to a more appropriate name, but it's the weather event) from the default Event Bridge.
template.yml
How was the Step Functions definition (workflow.asl.json) generated? Well I followed AWS's suggestion to built my first version of flow on Workflow Studio. Here's what it looks like in Workflow Studio:
Once I was happy with the flow, I exported the flow to json, and put it in my project folder (statemachine/workflow.asl.json).
The rule is simple: if temperature, humidity, time and city exist, insert the weather data into DynamoDB. Otherwise go to end state (do nothing).
statemachine/workflow.asl.json
Testing Step Functions
There are some resources to test Step Functions. I encourage you to take a look.
- Data flow simulator
2. Local development tools
Step Functions Transformation
Step Functions has various input and output variables. I found this blog and its sample application are really helpful explaining them.
DynamoDB
Weather data is being inserted into DynamoDB by Step Functions. Here’s the definition of DynamoDB table:
template.yml
Hash Key is “city” and Range Key is “datetime” (in unix time) because I want to query the DynamoDB by city, and sort the temperature data by time.
Here’s what data looks like in DynamoDB:
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