Serverless Functions(Node)

Serverless functions are pretty cool, they take care of another worry developers might have: What if I get so many requests that it overloads my server? Simple, you don't. You let an almost trillion dollar company(Amazon) handle it. These functions are able to scale up and down depending on the # of requests all handled by AWS Lambda.

We'll be using the serverless package which makes settings up AWS lambda pretty simple.

Before we begin, make sure you have a AWS account and user created and provide the user programmatic access:

1. Use the command: serverless config credentials --provider aws --key userKey --secret userSecret . Replace userKey and userSecret with the appropriate user information you created for the AWS account. 
2. Use the command serverless create --template aws-nodejs --path folderName . Replace folderName with your choice, this will create a folder with serverless.yml and a file called handler.js

There's really two parts that make up the serverless functions, the serverless.yml and the corresponding .js file containing the functions. For this example I'll have a file called handler.js containing all my functions I wish to make serverless.

When trying to hook up the functions, we must have a few things:

1. Define the functions in the file(handler.js)
2. Make sure the available handler is available for the function

In my handler.js file I'll have the two following functions

hello() which returns the message 'Hi' and bye() which returns the message 'Bye'.
Here's how bye looks like

module.exports.bye = async (event, context, callback)  => {
  const str = `Bye`;
  return str;
}

The event argument contains information about other AWS services the function has gone through, if it went through a load balancer it will contain information about the load balancer. For more information about it, find it here.

The context argument contains information about the invocation, function and environment. For more information about it, find it here.

The callback argument contains information you want to send back in case of success or error, the callback actually accepts two arguments callback(response_error, response_success). Amazon provides documentation on how you should handle async vs sync callbacks here

Make sure both functions are exported. In the .yml file under the functions: section you want to create a section for each.

functions:
  hello:
    handler: handler.hello
    events:
        - http:
             path: users/hello
             method: get

  bye:
    handler: handler.bye
    events:
        - http:
             path: users/bye
             method: get

You'll notice we have the function name, followed by handler: fileName.functionName.

To push the code to AWS, we'll have to use the command serverless deploy -v, you'll have to push the code anytime you want the changes reflected on AWS

To call any of the functions to test on command line, use the command serverless invoke -f functionName

To test your app locally, we'll be using serverless-offline package. Once the package has been installed, we have to add the following at the end of serverless.yml:

plugins:
  - serverless-offline

Use the command serverless offline start to start it up locally. This uses default port 3000 and you should now be able to get 'Bye' in the terminal or console when you hit the route: localhost:3000/users/bye

This wasn't too bad. Now you can say you have knowledge of cloud based programming!

Source: https://hackernoon.com/a-crash-course-on-serverless-with-node-js-632b37d58b44