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We're prompted to create a new lambda function and I want to do so because it's finally time to

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re-run some code whenever we receive a request.

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However we don't have one,

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so let's first learn what lambda is before we dive into creating a function immediately.

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AWS lambda that is a service which allows you to host your code on it and run it upon certain events,

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this is how it looks in detail.

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We get different events sources,

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for example S3, this file storage service. A file upload could trigger a lambda function which then

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will receive info about that file as an input and could possibly transform it.

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This is useful if you have a service where people upload photos of themselves and you want to compress

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them, maybe analyze them with machine learning,

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you could do all that with lambda.

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Another example is cloud watch,

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here you can schedule events, so you can basically trigger a new lambda execution every

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X minutes, hours, days, it's useful for cleanup jobs or anything which runs on a regular basis.

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You can always use API Gateway to run the code whenever a request hits the API

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Gateway. This of course is the interesting use case for us,

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we also got other event sources but we will of course focus on the API Gateway here since this is what

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we typically use in this serverless approach

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when we talked about creating an API. Now this event source triggers our code next and this code is stored

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in lambda and written in NodeJS, Python, Java or C#,

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so PHP and so on is not supported,

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you have to choose one of these languages, only these language languages run in lambda.

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This code gets executed once your defined event occurs

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and in this code, you can do any calculation,

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reach out to other AWS services like a database to store or fetch data but any service is possible,

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you could also start sending mails here and in the end, you will return a response or you will execute

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a callback to indicate that this function is done, can shut down and possibly if needed, pass any data

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back to the event source who called it.

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This is how lambda works. In conjunction with API Gateway,

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we have multiple endpoints in API Gateway,

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some methods and resources and which trigger different lambda functions for each of these endpoints.

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And this is exactly what we're setting up here,

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so let's set it up in the next lecture.