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Feb 11, 2018

AWS Serverless Project Lambda Integration Part 3

First Read this

Understanding the lambda function Handler Read More…

Create IAM Policy

Review and use the below 3 files , download to a folder and execute the following command This will create a IAM Role and grants (2) permission to the Pet table and the Cloudwatch logs.

# Create the role and attach the trust policy that enables Lambda to assume this role.
$ aws iam create-role --role-name lambda-execution-serverless --assume-role-policy-document file://trustpolicy.json

# Embed the permissions policy (in this example an inline policy) to the role to specify what it is allowed to do.
$ aws iam put-role-policy --role-name lambda-execution-serverless --policy-name permission-dynamodb-serverless --policy-document file://dynamodb_permission_serverless.json
$ aws iam put-role-policy --role-name lambda-execution-serverless --policy-name permission-log-serverless --policy-document file://log_permission_serverless.json

After this step make a note of the arn:aws:iam::375525124878:role/lambda-execution-serverless from your command window

Login and review from console now !!

The Lambda function

We are going to use the below lambda function, which querries the DynamoDb for a pet using a hard-coded primary key. This also logs the informaton in the console.

var AWS = require("aws-sdk");
var docClient = new AWS.DynamoDB.DocumentClient();
exports.dynamo_query_pet_by_id = (event, context, callback) => {
var id = 1; // we will change this later
var params = {
    TableName : "Pet",
    KeyConditionExpression: "#id_key = :id_val",
        "#id_key": "id"
    ExpressionAttributeValues: {
docClient.query(params, function(err, data) {
    if (err) {
        console.error("Unable to query. Error:", JSON.stringify(err, null, 2));
    } else {
        console.log("Query succeeded.");
        data.Items.forEach(function(item) {
            //response has to structure this way for API Gateway to handle
            var response = {
                "statusCode": 200,
                "headers": {
                    "my_header": "my_value"
                "body": JSON.stringify(item), //data
                "isBase64Encoded": false
            callback(null,response); //returning call using callback

Create Above Lambda Function Using CLI

Review and use the below file

The below command lambda create-function uses all default values to create a query by pet id function.

$ aws lambda create-function --function-name "dynamo_query_pet_by_id" --runtime "nodejs6.10" --role "arn:aws:iam::374525349870:role/lambda-execution-serverless" --handler "dynamo_query_pet_by_id.dynamo_query_pet_by_id" --zip-file fileb://dynamo_query_pet_by_id.zip

Login to the console Lambda > Functions > dynamo_query_pet_by_id and review the function.

Test your Lambda

Login to the console and create a test function. Dont worry about passing values. Just execute the query. You should see a response from the DynamoDB becuase the primary key is hard coded into the function.

Hurrey !! You now have a working function that can query the DynamoDb


Lets integrate the AWS API Gateway to call out Lambda function , which in turn would call the DynamoDb.