Ruby AWS Lambda Handler

The automatically generated code for an AWS Lambda function using the Ruby 2.7 runtime looks like this:

File: lambda_function.rb (original version)

require 'json'

def lambda_handler(event:, context:) (1)
    # TODO implement
    { statusCode: 200, body: JSON.generate('Hello from Lambda!') } (2)
end

The lambda_handler function has two parameters:

event: This parameter is a hash that is used to pass in event data to the handler. It contains, among others, the information detailed in the following table:

Table 1. Contents of Event
Keys	Associated Value
`event['version']`	A string with the current version of this event object. Should be `'2.0'` at the time of this writing.
`event['queryStringParameters']`	A hash with the query string parameters (only if it actually has any).
`event['headers']`	A hash with all the headers from the request.
`event['body']`	A string with the request body (only if it actually has one).
`event['requestContext']['domainName']`	A string with the domain name of the server where the AWS Lambda function is hosted.
`event['requestContext']['http']['method']`	A string with the request HTTP method (`GET` or `POST`, for example).
`event['requestContext']['http']['path']`	A string with the request path (for example `/some_resource`).
`event['requestContext']['http']['protocol']`	A string with the HTTP version used by the request (`HTTP/1.1`, for example).

context: This parameter provides runtime information to your handler. Its type is LambdaContext.

The handler should return a hash from which the HTTP response will be constructed.

Table 2. Hash Keys for HTTP Response
Key	Description
`:statusCode`	An integer number with the HTTP response status code.
`:body`	A string with the response body. Typically, the result of calling `JSON.generate` method to produce JSON output.
`:headers`	This is an optional key, but if provided it should refer to a hash with additional response headers.