AWS Compute Blog

Implementing safe AWS Lambda deployments with AWS CodeDeploy

This post courtesy of George Mao, AWS Senior Serverless Specialist – Solutions Architect

AWS Lambda and AWS CodeDeploy recently made it possible to automatically shift incoming traffic between two function versions based on a preconfigured rollout strategy. This new feature allows you to gradually shift traffic to the new function. If there are any issues with the new code, you can quickly rollback and control the impact to your application.

Previously, you had to manually move 100% of traffic from the old version to the new version. Now, you can have CodeDeploy automatically execute pre- or post-deployment tests and automate a gradual rollout strategy. Traffic shifting is built right into the AWS Serverless Application Model (SAM), making it easy to define and deploy your traffic shifting capabilities. SAM is an extension of AWS CloudFormation that provides a simplified way of defining serverless applications.

In this post, I show you how to use SAM, CloudFormation, and CodeDeploy to accomplish an automated rollout strategy for safe Lambda deployments.

Scenario

For this walkthrough, you write a Lambda application that returns a count of the S3 buckets that you own. You deploy it and use it in production. Later on, you receive requirements that tell you that you need to change your Lambda application to count only buckets that begin with the letter “a”.

Before you make the change, you need to be sure that your new Lambda application works as expected. If it does have issues, you want to minimize the number of impacted users and roll back easily. To accomplish this, you create a deployment process that publishes the new Lambda function, but does not send any traffic to it. You use CodeDeploy to execute a PreTraffic test to ensure that your new function works as expected. After the test succeeds, CodeDeploy automatically shifts traffic gradually to the new version of the Lambda function.

Your Lambda function is exposed as a REST service via an Amazon API Gateway deployment. This makes it easy to test and integrate.

Prerequisites

To execute the SAM and CloudFormation deployment, you must have the following IAM permissions:

  • cloudformation:*
  • lambda:*
  • codedeploy:*
  • iam:create*

You may use the AWS SAM Local CLI or the AWS CLI to package and deploy your Lambda application. If you choose to use SAM Local, be sure to install it onto your system. For more information, see AWS SAM Local Installation.

All of the code used in this post can be found in this GitHub repository: https://github.com/aws-samples/aws-safe-lambda-deployments.

Walkthrough

For this post, use SAM to define your resources because it comes with built-in CodeDeploy support for safe Lambda deployments.  The deployment is handled and automated by CloudFormation.

SAM allows you to define your Serverless applications in a simple and concise fashion, because it automatically creates all necessary resources behind the scenes. For example, if you do not define an execution role for a Lambda function, SAM automatically creates one. SAM also creates the CodeDeploy application necessary to drive the traffic shifting, as well as the IAM service role that CodeDeploy uses to execute all actions.

Create a SAM template

To get started, write your SAM template and call it template.yaml.

AWSTemplateFormatVersion : '2010-09-09'
Transform: AWS::Serverless-2016-10-31
Description: An example SAM template for Lambda Safe Deployments.

Resources:

  returnS3Buckets:
    Type: AWS::Serverless::Function
    Properties:
      Handler: returnS3Buckets.handler
      Runtime: nodejs6.10
      AutoPublishAlias: live
      Policies:
        - Version: "2012-10-17"
          Statement: 
          - Effect: "Allow"
            Action: 
              - "s3:ListAllMyBuckets"
            Resource: '*'
      DeploymentPreference:
          Type: Linear10PercentEvery1Minute
          Hooks:
            PreTraffic: !Ref preTrafficHook
      Events:
        Api:
          Type: Api
          Properties:
            Path: /test
            Method: get

  preTrafficHook:
    Type: AWS::Serverless::Function
    Properties:
      Handler: preTrafficHook.handler
      Policies:
        - Version: "2012-10-17"
          Statement: 
          - Effect: "Allow"
            Action: 
              - "codedeploy:PutLifecycleEventHookExecutionStatus"
            Resource:
              !Sub 'arn:aws:codedeploy:${AWS::Region}:${AWS::AccountId}:deploymentgroup:${ServerlessDeploymentApplication}/*'
        - Version: "2012-10-17"
          Statement: 
          - Effect: "Allow"
            Action: 
              - "lambda:InvokeFunction"
            Resource: !Ref returnS3Buckets.Version
      Runtime: nodejs6.10
      FunctionName: 'CodeDeployHook_preTrafficHook'
      DeploymentPreference:
        Enabled: false
      Timeout: 5
      Environment:
        Variables:
          NewVersion: !Ref returnS3Buckets.Version

This template creates two functions:

  • returnS3Buckets
  • preTrafficHook

The returnS3Buckets function is where your application logic lives. It’s a simple piece of code that uses the AWS SDK for JavaScript in Node.JS to call the Amazon S3 listBuckets API action and return the number of buckets.

'use strict';

var AWS = require('aws-sdk');
var s3 = new AWS.S3();

exports.handler = (event, context, callback) => {
	console.log("I am here! " + context.functionName  +  ":"  +  context.functionVersion);

	s3.listBuckets(function (err, data){
		if(err){
			console.log(err, err.stack);
			callback(null, {
				statusCode: 500,
				body: "Failed!"
			});
		}
		else{
			var allBuckets = data.Buckets;

			console.log("Total buckets: " + allBuckets.length);
			callback(null, {
				statusCode: 200,
				body: allBuckets.length
			});
		}
	});	
}

Review the key parts of the SAM template that defines returnS3Buckets:

  • The AutoPublishAlias attribute instructs SAM to automatically publish a new version of the Lambda function for each new deployment and link it to the live alias.
  • The Policies attribute specifies additional policy statements that SAM adds onto the automatically generated IAM role for this function. The first statement provides the function with permission to call listBuckets.
  • The DeploymentPreference attribute configures the type of rollout pattern to use. In this case, you are shifting traffic in a linear fashion, moving 10% of traffic every minute to the new version. For more information about supported patterns, see Serverless Application Model: Traffic Shifting Configurations.
  • The Hooks attribute specifies that you want to execute the preTrafficHook Lambda function before CodeDeploy automatically begins shifting traffic. This function should perform validation testing on the newly deployed Lambda version. This function invokes the new Lambda function and checks the results. If you’re satisfied with the tests, instruct CodeDeploy to proceed with the rollout via an API call to: codedeploy.putLifecycleEventHookExecutionStatus.
  • The Events attribute defines an API-based event source that can trigger this function. It accepts requests on the /test path using an HTTP GET method.
'use strict';

const AWS = require('aws-sdk');
const codedeploy = new AWS.CodeDeploy({apiVersion: '2014-10-06'});
var lambda = new AWS.Lambda();

exports.handler = (event, context, callback) => {

	console.log("Entering PreTraffic Hook!");
	
	// Read the DeploymentId & LifecycleEventHookExecutionId from the event payload
    var deploymentId = event.DeploymentId;
	var lifecycleEventHookExecutionId = event.LifecycleEventHookExecutionId;

	var functionToTest = process.env.NewVersion;
	console.log("Testing new function version: " + functionToTest);

	// Perform validation of the newly deployed Lambda version
	var lambdaParams = {
		FunctionName: functionToTest,
		InvocationType: "RequestResponse"
	};

	var lambdaResult = "Failed";
	lambda.invoke(lambdaParams, function(err, data) {
		if (err){	// an error occurred
			console.log(err, err.stack);
			lambdaResult = "Failed";
		}
		else{	// successful response
			var result = JSON.parse(data.Payload);
			console.log("Result: " +  JSON.stringify(result));

			// Check the response for valid results
			// The response will be a JSON payload with statusCode and body properties. ie:
			// {
			//		"statusCode": 200,
			//		"body": 51
			// }
			if(result.body == 9){	
				lambdaResult = "Succeeded";
				console.log ("Validation testing succeeded!");
			}
			else{
				lambdaResult = "Failed";
				console.log ("Validation testing failed!");
			}

			// Complete the PreTraffic Hook by sending CodeDeploy the validation status
			var params = {
				deploymentId: deploymentId,
				lifecycleEventHookExecutionId: lifecycleEventHookExecutionId,
				status: lambdaResult // status can be 'Succeeded' or 'Failed'
			};
			
			// Pass AWS CodeDeploy the prepared validation test results.
			codedeploy.putLifecycleEventHookExecutionStatus(params, function(err, data) {
				if (err) {
					// Validation failed.
					console.log('CodeDeploy Status update failed');
					console.log(err, err.stack);
					callback("CodeDeploy Status update failed");
				} else {
					// Validation succeeded.
					console.log('Codedeploy status updated successfully');
					callback(null, 'Codedeploy status updated successfully');
				}
			});
		}  
	});
}

The hook is hardcoded to check that the number of S3 buckets returned is 9.

Review the key parts of the SAM template that defines preTrafficHook:

  • The Policies attribute specifies additional policy statements that SAM adds onto the automatically generated IAM role for this function. The first statement provides permissions to call the CodeDeploy PutLifecycleEventHookExecutionStatus API action. The second statement provides permissions to invoke the specific version of the returnS3Buckets function to test
  • This function has traffic shifting features disabled by setting the DeploymentPreference option to false.
  • The FunctionName attribute explicitly tells CloudFormation what to name the function. Otherwise, CloudFormation creates the function with the default naming convention: [stackName]-[FunctionName]-[uniqueID].  Name the function with the “CodeDeployHook_” prefix because the CodeDeployServiceRole role only allows InvokeFunction on functions named with that prefix.
  • Set the Timeout attribute to allow enough time to complete your validation tests.
  • Use an environment variable to inject the ARN of the newest deployed version of the returnS3Buckets function. The ARN allows the function to know the specific version to invoke and perform validation testing on.

Deploy the function

Your SAM template is all set and the code is written—you’re ready to deploy the function for the first time. Here’s how to do it via the SAM CLI. Replace “sam” with “cloudformation” to use CloudFormation instead.

First, package the function. This command returns a CloudFormation importable file, packaged.yaml.

sam package –template-file template.yaml –s3-bucket mybucket –output-template-file packaged.yaml

Now deploy everything:

sam deploy –template-file packaged.yaml –stack-name mySafeDeployStack –capabilities CAPABILITY_IAM

At this point, both Lambda functions have been deployed within the CloudFormation stack mySafeDeployStack. The returnS3Buckets has been deployed as Version 1:

SAM automatically created a few things, including the CodeDeploy application, with the deployment pattern that you specified (Linear10PercentEvery1Minute). There is currently one deployment group, with no action, because no deployments have occurred. SAM also created the IAM service role that this CodeDeploy application uses:

There is a single managed policy attached to this role, which allows CodeDeploy to invoke any Lambda function that begins with “CodeDeployHook_”.

An API has been set up called safeDeployStack. It targets your Lambda function with the /test resource using the GET method. When you test the endpoint, API Gateway executes the returnS3Buckets function and it returns the number of S3 buckets that you own. In this case, it’s 51.

Publish a new Lambda function version

Now implement the requirements change, which is to make returnS3Buckets count only buckets that begin with the letter “a”. The code now looks like the following (see returnS3BucketsNew.js in GitHub):

'use strict';

var AWS = require('aws-sdk');
var s3 = new AWS.S3();

exports.handler = (event, context, callback) => {
	console.log("I am here! " + context.functionName  +  ":"  +  context.functionVersion);

	s3.listBuckets(function (err, data){
		if(err){
			console.log(err, err.stack);
			callback(null, {
				statusCode: 500,
				body: "Failed!"
			});
		}
		else{
			var allBuckets = data.Buckets;

			console.log("Total buckets: " + allBuckets.length);
			//callback(null, allBuckets.length);

			//  New Code begins here
			var counter=0;
			for(var i  in allBuckets){
				if(allBuckets[i].Name[0] === "a")
					counter++;
			}
			console.log("Total buckets starting with a: " + counter);

			callback(null, {
				statusCode: 200,
				body: counter
			});
			
		}
	});	
}

Repackage and redeploy with the same two commands as earlier:

sam package –template-file template.yaml –s3-bucket mybucket –output-template-file packaged.yaml
	
sam deploy –template-file packaged.yaml –stack-name mySafeDeployStack –capabilities CAPABILITY_IAM

CloudFormation understands that this is a stack update instead of an entirely new stack. You can see that reflected in the CloudFormation console:

During the update, CloudFormation deploys the new Lambda function as version 2 and adds it to the “live” alias. There is no traffic routing there yet. CodeDeploy now takes over to begin the safe deployment process.

The first thing CodeDeploy does is invoke the preTrafficHook function. Verify that this happened by reviewing the Lambda logs and metrics:

The function should progress successfully, invoke Version 2 of returnS3Buckets, and finally invoke the CodeDeploy API with a success code. After this occurs, CodeDeploy begins the predefined rollout strategy. Open the CodeDeploy console to review the deployment progress (Linear10PercentEvery1Minute):

Verify the traffic shift

During the deployment, verify that the traffic shift has started to occur by running the test periodically. As the deployment shifts towards the new version, a larger percentage of the responses return 9 instead of 51. These numbers match the S3 buckets.

A minute later, you see 10% more traffic shifting to the new version. The whole process takes 10 minutes to complete. After completion, open the Lambda console and verify that the “live” alias now points to version 2:

After 10 minutes, the deployment is complete and CodeDeploy signals success to CloudFormation and completes the stack update.

Check the results

If you invoke the function alias manually, you see the results of the new implementation.

aws lambda invoke –function [lambda arn to live alias] out.txt

You can also execute the prod stage of your API and verify the results by issuing an HTTP GET to the invoke URL:

Summary

This post has shown you how you can safely automate your Lambda deployments using the Lambda traffic shifting feature. You used the Serverless Application Model (SAM) to define your Lambda functions and configured CodeDeploy to manage your deployment patterns. Finally, you used CloudFormation to automate the deployment and updates to your function and PreTraffic hook.

Now that you know all about this new feature, you’re ready to begin automating Lambda deployments with confidence that things will work as designed. I look forward to hearing about what you’ve built with the AWS Serverless Platform.