AWS Serverless

Introduction

This is an example of how to set up a serverless framework function within AWS

Setup

Within AWS there are example templates for each piece of the infrastructure. For this we need to create a

• S3 Bucket to hold the code
• IAM::Role to describe the permissions
• Lambda The function to run
• Bucket Policy This grants access from the bucket to the lambda function

Templates

Here are the templates I used. I have highlighted where they differ from the provided examples

Stack cowsay-bucket

S3 Bucket

Example can be found here
This needs to be in its own stack and create prior to the other resources.

{
    "Resources": {
        "cowsayBucket": {
            "Type": "AWS::S3::Bucket",
            "Properties": {
                "BucketName": "cowsayBucket"
            }
        }
    }
}

Stack cowsay-lambda

This stack or group of resources holds the lamda, bucket policy and role. The lambda function references the bucket created above.

IAM::Role

Example can be found here

{
    "Resources": {
        "cowsayIamRole": {
            "Type": "AWS::IAM::Role",
            "Properties": {
                "AssumeRolePolicyDocument": {
                    "Version": "2012-10-17",
                    "Statement": [
                        {
                            "Effect": "Allow",
                            "Principal": {
                                "Service": [
                                    "lambda.amazonaws.com"
                                ]
                            },
                            "Action": [
                                "sts:AssumeRole"
                            ]
                        }
                    ]
                },
                "Path": "/",
                "Policies": [
                    {
                        "PolicyName": "root",
                        "PolicyDocument": {
                            "Version": "2012-10-17",
                            "Statement": [
                                {
                                    "Effect": "Allow",
                                    "Action": [
                                        "logs:*"
                                    ],
                                    "Resource": "arn:aws:logs:*:*:*"
                                }
                            ]
                        }
                    }
                ]
            }
        }
    }
}

Lambda Function

Example can be found here

{
    "Resources": {
        "cowsayLambda": {
            "Type": "AWS::Lambda::Function",
            "Properties": {
                "Code": {
                    "S3Bucket": "cowsaybucket",
                    "S3Key": "cowsay.zip"
                },
                "Handler": "index.handler",
                "Runtime": "nodejs14.x",
                "Role": {
                    "Fn::GetAtt": [
                        "cowsayIamRole",
                        "Arn"
                    ]
                }
            }
        }
    }
}

Adding the Role to the Lambda

Now we have the base templates we need to add properties to allow them to interact

{
    "Resources": {
        "cowsayBucket": {
            "Type": "AWS::S3::Bucket",
            "Properties": {
                "BucketName": "cowsayBucket"
            }
        },
        "Role": {
            "Ref": "cowsayIamRole"
        }
    }
}

Bucket Policy

We need to allow lambda function access to the bucket. We do this with a the bucket

{
    "Resources": {
        "cowsayBucketPolicy": {
            "Type": "AWS::S3::BucketPolicy",
            "Properties": {
                "Bucket": "cowsaybucket",
                "PolicyDocument": {
                    "Statement": [
                        {
                            "Effect": "Allow",
                            "Principal": {
                                "Service": "serverlessrepo.amazonaws.com"
                            },
                            "Action": "s3:GetObject",
                            "Resource": "arn:aws:s3:::cowsaybucket/*",
                            "Condition": {
                                "StringEquals": {
                                    "aws:SourceArn": {
                                        "Fn::GetAtt": [
                                            "cowsayLambda",
                                            "Arn"
                                        ]
                                    }
                                }
                            }
                        }
                    ]
                }
            }
        }
    }
}

The Code

Do do this we

• Create a node js package
• Create a function
• Create a template to run it locally

Create a node js package

Just a straight forward package

{
  "name": "cowsay",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "author": "",
  "license": "ISC",
  "dependencies": {
    "cowsay": "^1.4.0"
  }
}

Create a function

const cowsay = require('cowsay');
exports.handler = function(event, context) {
    // Get a cow from cowsay!
    let cow = cowsay.say({
        text: "I'm a lambda moooodule",
        e: "oO",
        T: "U "
    });
// Replace line breaks to HTML line breaks
    cow = cow.replace(/[\n|\r|\n\r]/g, '<br />');
// Create the HTML
    var html = '<html><head><title>Cowsay Lambda!</title></head>' + 
        `<body><h1>Welcome to Cowsay Lambda!</h1>${cow}</body></html>`;
    
    // New Source 1
            
    // Return the HTML response
    context.succeed(html);
};

Create a template to run it locally

See here for documentation.

AWSTemplateFormatVersion: '2010-09-09'
Transform: 'AWS::Serverless-2016-10-31'
Description: An AWS Serverless Specification template describing your function.
Resources:
  myfirstlambda:
    Type: 'AWS::Serverless::Function'
    Properties:
      Handler: index.handler
      Runtime: nodejs14.x
      CodeUri: .
      Description: ''
      MemorySize: 128
      Timeout: 3

We need to create a function. We create a package and function

Uploading the code

We need to upload the code to the S3Bucket we created above. We need to zip it up making sure that index.js is at the root and not in a folder. Remember you need the code as well. It does not build it in the cloud.

cd <myproject>
zip -r cowsay.zip *

We can upload it by right-clicking lambda and choosing upload lambda

Running the Code

To run the code locally type

sam local invoke

To run the code on AWS right click on the lambda within AWS Explorer in VS Code