Tag Archives: Lambda

Get User Id in Lambda node.js

Hi everyone,

A quick post on where to find the user id (sub) in a lambda requested that has been authenticated with a congito authorizer.

You’ll be able to find everything you need in the event object under requestContext > authorizer > claims:

exports.viewContextHandler = async (event, context, callback) => {

"requestContext": {
    "resourceId": "XXXXX",
    "authorizer": {
        "claims": {
            "at_hash": "XXXXX",
            "sub": "XXXXX-XXXXX-XXXXX-XXXXX-XXXXX",
            "aud": "XXXXX12341234512345XXXXX",
            "email_verified": "true",
            "token_use": "id",
            "auth_time": "1547371205",
            "iss": "https://cognito-XXXXX.com/XXXXX",
            "cognito:username": "XXXXX-XXXXX-XXXXX-XXXXX-XXXXX",
            "exp": "Sun Jan 13 10:20:05 UTC 2019",
            "iat": "Sun Jan 13 09:20:05 UTC 2019",
            "email": "XXXXX@XXXXX.XXXXX"

Upload an Image to S3 Using Post and a Presigned Url

Hi everyone,

Today I’ve been converting my “PUT” upload to S3 to a “POST”. The main motivator for this was to restrict the file size of uploads using a signed policy. Unfortunately this was a pretty tedious process and the error responses from S3 were very vague. Thankfully it’s working now and here’s what I needed to do!

Here’s an excerpt from my nodejs lambda function that generates the presigned url:

/* Creates a pre-signed upload url and then stores a reference in a table */
exports.createUploadUrl = async params => {

    var { databaseHandler, bucketHandler } = params;

    // Create id for upload
    var uploadId = uuidv4();

    // Retrieve pre-signed url
    var bucketDataPromise = createPresignedPostPromise({
        Bucket: process.env.BUCKET_UPLOADS,
        Expires: 60 * 60,
        Conditions: [            
            ["content-length-range", 0, 300000], // 300kb
            [ "eq", "$key", uploadId],
            [ "eq", "$Content-Type", 'image/jpeg' ],

    // var ddbData = await ddbDataPromise;
    var bucketData = await bucketDataPromise;

    // Wait for database handler to complete operation and then return
    return Helpers.generateResponse({
        data: {
            uploadData: bucketData,
            additionalFields: {
                key: uploadId,
                "Content-Type": 'image/jpeg',
        statusCode: 200

You can then retrieve the upload details using a request like the following (Python):

resp = requests.put("https://f86caxqe9f.execute-api.ap-southeast-2.amazonaws.com/Prod/images", data=open(path, 'rb'))

This will return a response similar to the following:

    "messages": [],
    "data": {
        "uploadUrl": {
            "url": "YOUR UPLOAD URL",
            "fields": {
                "bucket": "YOUR BUCKET",
                "X-Amz-Algorithm": "AWS4-HMAC-SHA256",
                "X-Amz-Credential": "XXX",
                "X-Amz-Date": "20190107T125044Z",
                "X-Amz-Security-Token": "SECURITY_TOKEN",
                "Policy": "YOUR BASE64 ENCODED POLICY",
                "X-Amz-Signature": "SIGNATURE"
        "uploadId": "UPLOAD_ID"

And once you have those details you can use them to upload the image:

# Attempt to retrieve upload url etc
json = resp.json()
data = json["data"]
uploadUrl = data["uploadData"]["url"]
uploadFields = data["uploadData"]["fields"]

    print("Uploading image...",end='')
    headers = {'Content-Type': 'multipart/form-data' }
    files = { 'file': open(path, 'rb')}
    resp = requests.post(uploadUrl, data=uploadFields, files=files)

    # Only show content if there's an error
    if resp.status_code == 200:

except Exception as e:
    print("\r\nFailed to upload image.")
    print("Upload data:")

Hopefully that’s been able to help you out, but feel free to let me know in the comments below if you need more info!

Thanks to these links for the info:

AWS SAM Cheat Sheet/Quick Reference

Hi everyone,

This will just be a living cheat sheet or quick reference for using AWS SAM with nodejs. I’ll add to it as I find things that are useful or I might need again.

General AWS SAM Info:

Description Example More
Validate template sam validate
Start AWS Sam Locally https://docs.aws.amazon.com/serverless-application-model/latest/developerguide/serverless-quick-start.html
Access config variable in Lambda const CAT_BREED_TABLE = process.env.CAT_BREED_TABLE; https://stackoverflow.com/a/48491845/522859
Dynamically reference another resource in template.yml CAT_BREED_TABLE: !Ref DynamoDbCatBreedTable https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/intrinsic-function-reference-ref.html

Dynamo DB Local Info:

Description Example More
Create table aws dynamodb create-table –table-name CatBreeds –attribute-definitions AttributeName=CatBreedId,AttributeType=S –key-schema AttributeName=CatBreedId,KeyType=HASH –provisioned-throughput ReadCapacityUnits=5,WriteCapacityUnits=5
List Tables aws dynamodb list-tables –endpoint-url https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/Tools.CLI.html
List All Rows in Table aws dynamodb scan –table-name PestinatorTable –endpoint-url https://stackoverflow.com/a/52236600/522859

Node.js Info:

Description Example More
Run tests npm test

Parsing DynamoDB Items – AWS Lambda with Node.js

Hi everyone,

A quick post on how to parse DynamoDB items into something more readable when using lambda with Node.js:



    CatBreedId: { S: '17acbc81-2b4a-462b-be87-bcc49580b1ae'},
    Name: { S: 'Cat #1'}



    "CatBreedId": "17acbc81-2b4a-462b-be87-bcc49580b1ae",
    "Name": "Cat #1"

Official doco is here: https://docs.aws.amazon.com/AWSJavaScriptSDK/latest/AWS/DynamoDB/Converter.html

Thanks to the following stackoverflow post for the info: https://stackoverflow.com/a/44536616/522859

AWS 2_ContinuousDeliveryPipeline Tutorial – Error: no test specified

Hi everyone,

I ran into the following error while completing an AWS tutorial: https://github.com/aws-samples/aws-serverless-workshops/tree/master/DevOps/2_ContinuousDeliveryPipeline

C:UsersChris-PCsourcereposUniApiuni-apitest>npm test

> uni-api-test@1.0.0 test C:UsersChris-PCsourcereposUniApiuni-api
> echo ‘Error: no test specified’

‘Error: no test specified’

The solution was to add the following line to my package.json file:

“scripts”: {“test”: “mocha”}

Now when running npm test I get the expected test output:

4 passing (24ms)
1 failing

1) Reading Unicorns
errors on missing unicorn data:

AssertionError [ERR_ASSERTION]: 500 == 404
+ expected – actual


at lambda.lambda_handler (testread.spec.js:77:20)
at appread.js:20:10
at Object.get (testread.spec.js:34:33)
at Object.exports.lambda_handler (appread.js:18:13)
at Context. (testread.spec.js:65:16)

npm ERR! Test failed. See above for more details.

Thanks to this link for the answer: https://teamtreehouse.com/community/when-i-run-test-i-am-getting-an-error-that-says-no-test-specified

An error occurred (UnrecognizedClientException) when calling the CreateFunction operation: The security token included in the request is invalid.

Hi everyone,

I ran into the following error today while attempting to create a Lambda function using the CLI:

An error occurred (UnrecognizedClientException) when calling the CreateFunction operation: The security token included in the request is invalid.

The first thing to check is that your aws config is setup correctly. For me this is under c:userschris-pc.aws.

If that looks fine, double check that the associated user has the correct rights by viewing the IAM page in the server console: https://console.aws.amazon.com/iam/home

Finally, ensure that the user has programmatic access and that the keys match those in your config.