Lambda Snapstart with Serverless framework

This has got to be one of the worst feature launches that I have seen in a long time. How the AWS team could put in all the time and effort required to bring this feature to market, while simultaneously rendering it useless, because we can’t script the thing is beyond me.

We were ready to jump on this and start migrating apps to lambda, but now we are back in limbo. Even knowing there was a fix coming down the line would be something. Hopefully somebody from the AWS lambda team can provide some insights…

Here is a working POC of a serverless plugin that updates the lambda references to use the most recent version. This fixed the resulting cloud formation code and was tested with both SQS and API-Gateway.

'use strict'

class SetCycle {
  constructor (serverless, options) {
    this.hooks = {
      // this is where we declare the hook we want our code to run
      'before:package:finalize': function () { snapShotIt(serverless) }
    }
  }
}

function traverse(jsonObj,functionVersionMap) {
    if( jsonObj !== null && typeof jsonObj == "object" ) {
        Object.entries(jsonObj).forEach(([key, value]) => {
            if(key === 'Fn::GetAtt' && value.hasOwnProperty('length') && value.length === 2 && value[1] === "Arn" && functionVersionMap.get(value[0])){
                console.log(jsonObj);
                let newVersionedMethod = functionVersionMap.get(value[0]);
                
                delete jsonObj[key];
                jsonObj.Ref = newVersionedMethod;
                
                console.log('--becomes');
                console.log(jsonObj);
            }else{
            // key is either an array index or object key
                traverse(value,functionVersionMap);
            }
        });
    }
    else {
        // jsonObj is a number or string
    }
}

function snapShotIt(serverless){
    resetLambdaReferencesToVersionedVariant (serverless)
}

function resetLambdaReferencesToVersionedVariant (serverless) {
  
  const functionVersionMap = new Map();
  
  let rsrc = serverless.service.provider.compiledCloudFormationTemplate.Resources
  // build a map of all the lambda methods and their associated versioned resource
  for (let key in rsrc) {
    if (rsrc[key].Type === 'AWS::Lambda::Version') {
      functionVersionMap.set(rsrc[key].Properties.FunctionName.Ref,key);
    }
  }
 
  
  // loop through all the resource and replace the non-verioned with the versioned lambda arn reference
  for (let key in rsrc) {
    if (! (rsrc[key].Type === 'AWS::Lambda::Version' || rsrc[key].Type === 'AWS::Lambda::Function')) {
      console.log("--" + key);
      traverse(rsrc[key],functionVersionMap);
    }
  }
  
  // add the snapshot syntax
  for (let key in rsrc) {
    if (rsrc[key].Type === 'AWS::Lambda::Function') {
      console.log(rsrc[key].Properties);
      rsrc[key].Properties.SnapStart = {"ApplyOn": "PublishedVersions"};
      console.log("--becomes");
      console.log(rsrc[key].Properties);
    }
  }

  // prints the method map
  //for(let [key,value] of functionVersionMap){
    //console.log(key + " : " + value);
  //}

}

// now we need to make our plugin object available to the framework to execute
module.exports = SetCycle