Providing multiple api versions on API Gateway and Lambda using Serverlesss Framework

Question

I'm building a serverless app using API Gateway and Lambda (Serverless Framework) and trying to find a way to provide multiple versions of our app's API.

Here's the way I can think of.

serverless.yml

 handler: list.handler
 events:
     - http:
         path: {ver}/list
         method: get
         cors: true
         authorizer: aws_iam

list.js

 export async function handler(event, context, callback) {
     const ver = event.pathParameters.ver;
     if (ver >= '1.0') {
         return fooUtil.getNo(ver);
     } else {
         return 1;
     }  
 }

fooUtil.js

 export function getNo(ver) {
     if (ver >= 1.3) {
         return 3;
     } else {
         return 2;
     }
 }

However, I need to pass "ver" parameter to all functions this way.

Is there any way easier (and testable) to fetch version no from request like below?

fooUtil.js

 export function getNo() {
     if (session.getValue('ver') >= 1.3) {
     }
 }

I prefer not to divide repositories or git branches to manage multiple versions.

Answer 1

What is about to have for each version its own resource and separate it by folders?

Like this

 handler: v1.list.handler
 events:
     - http:
         path: v1/list
         method: get
         cors: true
         authorizer: aws_iam

 handler: v2.list.handler
 events:
     - http:
         path: v2/list
         method: get
         cors: true
         authorizer: aws_iam

That gives you the flexibility to test everything and its easier for newcomers to your project because the versioning is explicit through folder separation.

Answer 2

After reading many sources and trying to understand how AWS API Gateway works (from the versioning perspective), I decided to simply duplicate the API on my major versions and keep track on them through diff branches. The benefits:

• Update/Remove each version without impacting any other version. Ex: If I am on V4 and want to make changes on V1 I just switch branches, make my changes and then push the code.
• The versioning may not be only on Lambda Level. It could have proxies and may have changes on their structure as well.
• This will help on deployment process, as the clients could move gradually to a new version but still have access to the old one.
• It will help to keep track of the history of each version.
• I will have a isolated flow for my CI/CD.
• Each version will have a new domain. v1.maindomain.com/api, v2.maindomain.com/api
• Easy to any developer of any level to understand and maintain.
• To create a new version, I just create a new branch and update the version at the config file.

I am using serverless-custom-domain which creates a recordset during my deployment.