Serverless-ly Query External REST API from AWS and Store Results in S3? - amazon-web-services

Question

Given a REST API, outside of my AWS environment, which can be queried for json data:
https://someExternalApi.com/?date=20190814
How can I setup a serverless job in AWS to hit the external endpoint on a periodic basis and store the results in S3?
I know that I can instantiate an EC2 instance and just setup a cron. But I am looking for a serverless solution, which seems to be more idiomatic.
Thank you in advance for your consideration and response.

Answer 1

Yes, you absolutely can do this, and probably in several different ways!
The pieces I would use would be:
CloudWatch Event using a cron-like schedule, which then triggers...
A lambda function (with the right IAM permissions) that calls the API using eg python requests or equivalent http library and then uses the AWS SDK to write the results to an S3 bucket of your choice:
An S3 bucket ready to receive!
This should be all you need to achieve what you want.

Answer 2

I'm going to skip the implementation details, as it is largely outside the scope of your question. As such, I'm going to assume your function already is written and targets nodeJS.
AWS can do this on its own, but to make it simpler, I'd recommend using Serverless. We're going to assume you're using this.
Assuming you're entirely new to serverless, the first thing you'll need to do is to create a handler:
serverless create --template "aws-nodejs" --path my-service
This creates a service based on the aws-nodejs template on the provided path. In there, you will find serverless.yml (the configuration for your function) and handler.js (the code itself).
Assuming your function is exported as crawlSomeExternalApi on the handler export (module.exports.crawlSomeExternalApi = () => {...}), the functions entry on your serverless file would look like this if you wanted to invoke it every 3 hours:
functions:
crawl:
handler: handler.crawlSomeExternalApi
events:
- schedule: rate(3 hours)
That's it! All you need now is to deploy it through serverless deploy -v
Below the hood, what this does is create a CloudWatch schedule entry on your function. An example of it can be found over on the documentation

Answer 3

First thing you need is a Lambda function. Implement your logic, of hitting the API and writing data to S3 or whatever, inside the Lambda function. Next thing, you need a schedule to periodically trigger your lambda function. Schedule expression can be used to trigger an event periodically either using a cron expression or a rate expression. The lambda function you created earlier should be configured as the target for this CloudWatch rule.
The resulting flow will be, CloudWatch invokes the lambda function whenever there's a trigger (depending on your CloudWatch rule). Lambda then performs your logic.