DynamoDB document client put method works on a local DynamoDB instance but does not work inside AWS Lambda

Question

I have created a Table inside a local DynamoDB instance and in AWS using:

var AWS = require("aws-sdk");

AWS.config.update({
  region: "us-west-2"
  // Uncomment the following line to create the table locally.
  //endpoint: "http://localhost:8000"
});

var dynamodb = new AWS.DynamoDB();

var params = {
    TableName : "ProductView",
    KeySchema: [       
        { AttributeName: "id", KeyType: "HASH"},  //Partition key
        { AttributeName: "description", KeyType: "RANGE" }  //Sort key
    ],
    AttributeDefinitions: [       
        { AttributeName: "id", AttributeType: "N" },
        { AttributeName: "description", AttributeType: "S" }
    ],
    ProvisionedThroughput: {       
        ReadCapacityUnits: 10, 
        WriteCapacityUnits: 10
    }
};

dynamodb.createTable(params, function(err, data) {
    if (err) {
        console.error("Unable to create table. Error JSON:", JSON.stringify(err, null, 2));
    } else {
        console.log("Created table. Table description JSON:", JSON.stringify(data, null, 2));
    }
});

I can add a new item to the local and remote tables executing this:

console.log('Loading function');
var AWS = require("aws-sdk");

AWS.config.update({
    region: "us-west-2"
    // Uncomment the following line to add the item locally.
    //endpoint: "http://localhost:8000"
});

var docClient = new AWS.DynamoDB.DocumentClient();

var table = "ProductView";



var id = 1;
var description = "This is only a test";

var params = {
    TableName: table,
    Item: {
        "id": id,
        "description": description
    }
};

console.log("Adding a new item...");
docClient.put(params, function (err, data) {
    if (err) {
        console.error("Unable to add item. Error JSON:", JSON.stringify(err, null, 2));
    } else {
        console.log("Added item:", JSON.stringify(data, null, 2));
    }
});

However, if I use that code inside a Lambda as:

console.log('Loading function');
var AWS = require("aws-sdk");

var docClient = new AWS.DynamoDB.DocumentClient();

var table = "ProductView";

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

    var id = 1;
    var description = "This is only a test";

    var params = {
        TableName: table,
        Item: {
            "id": id,
            "description": description
        }
    };

    console.log("Adding a new item...");
    docClient.put(params, function (err, data) {
        if (err) {
            console.error("Unable to add item. Error JSON:", JSON.stringify(err, null, 2));
        } else {
            console.log("Added item:", JSON.stringify(data, null, 2));
        }
    });
    

}

The item won't get added and neither of the logging statements inside the callback get printed.

The item will be added in the AWS table if use this code inside the Lambda though:

console.log('Loading function');
var AWS = require("aws-sdk");

var docClient = new AWS.DynamoDB.DocumentClient();

var table = "ProductView";

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

    var id = 1;
    var description = "This is only a test";

    var params = {
        TableName: table,
        Item: {
            "id": id,
            "description": description
        }
    };

    console.log("Adding a new item...");
    await docClient.put(params).promise();

}

Why does the callback approach work in the local DynamoDB Table but not inside the Lambda against the Table in the cloud?

Answer 1

If you want to use callback then you need to use callback style lambda handler and invoke the handler callback in the callback from the put. It doesn't matter that it works locally without it, it's free to do whatever it wants given the wrong code.