The "AutoMaTweet"

At MindTouch, the company that I’m currently working for, we have been hosting a series of hands-on meetups focused on C# and AWS Lambda called λ# (Lambda Sharp). These are 3 hour hackathons where people are placed in random teams and get to learn, colaborate and have a lot of fun! Since I have been learning scala in my own time, I decided to implement one of the most fun challenges to date: The AutoMaTweet.

The AutoMaTweet is a simple AWS Lambda Function that is invoked every time an image is uploaded to an S3 bucket. The funciton will download the image and use a service called rekognition to analize the image and get “tags” or “lables” for the image. Finally the image is posted to twitter using a custom message created based on the labels:

You can find the challange in this github repository, and the Scala solution in my github account

Setup Guide

Clone repository

clone or fork the following github repository:

git clone https://github.com/onema/TheAutoMaTweet

Create a new AWS S3 bucket

aws s3api create-bucket --bucket <DEPLOYMENT BUCKET NAME>
aws s3api create-bucket --bucket <IMAGES BUCKET NAME>

Create a role for the lambda function

This role will contain the policy allowing the lambda function to get objects from S3 and use the Rekognition API

aws iam create-role \
    --role-name scala-lambda-role \
    --assume-role-policy-document file://trust-policy.json

{
    "Role": {
        "AssumeRolePolicyDocument": {
            "Version": "2012-10-17",
            "Statement": [
                {
                    "Action": "sts:AssumeRole",
                    "Effect": "Allow",
                    "Principal": {
                        "Service": "lambda.amazonaws.com"
                    }
                }
            ]
        },
        "RoleId": "FEDCBA987654321",
        "CreateDate": "2017-03-24T04:39:08.518Z",
        "RoleName": "scala-lambda-role",
        "Path": "/",
        "Arn": "arn:aws:iam::123456789012:role/scala-lambda-role"
    }
}

Create a policy

I have included a simple policy file. PLEASE NOTE THIS POLICY IS VERY OPEN AND SHOULD ONLY BE USED FOR TEST APPS

aws iam create-policy \
    --policy-name scala-lambda-s3-rekognition-policy \
    --policy-document file://policy.json

{
    "Policy": {
        "PolicyName": "scala-lambda-s3-rekognition-policy",
        "CreateDate": "2017-03-24T05:03:31.319Z",
        "AttachmentCount": 0,
        "IsAttachable": true,
        "PolicyId": "ABCDEF123456",
        "DefaultVersionId": "v1",
        "Path": "/",
        "Arn": "arn:aws:iam::123456789012:policy/scala-lambda-s3-rekognition-policy",
        "UpdateDate": "2017-03-24T05:03:31.319Z"
    }
}

NOTE: Take a note of the ARN returned by this call!

Attach the policy to the role

aws iam attach-role-policy \
    --role-name scala-lambda-role \
    --policy-arn <POLICY ARN>

Compile the project and upload it to S3

stb compile
sbt assembly
aws s3 cp target/scala-2.12/LambdaScala-assembly-1.0.jar s3://<DEPLOYMENT BUCKET NAME>/LambdaScala-assembly-1.0.jar

Create the lambda function

aws lambda create-function \
    --function-name scala-lambda-function \
    --runtime java8 \
    --timeout 30 \
    --memory-size 256 \
    --handler "lambda.AutoMaTweet::lambdaHandler" \
    --code S3Bucket=<DEPLOYMENT BUCKET NAME>,S3Key=LambdaScala-assembly-1.0.jar \
    --role <ROLE ARN>

Wrapping it all up

Create a trigger

At this point login to AWS go to lambda and click on your new function.

Select Triggers > Add trigger > S3

Make sure to select the Bucket: and the Event type: Object Created (All) and click on Submit

Set the environment variables

These values are used to access your twitter application (go to https://apps.twitter.com/ if you don’t have one). Create the following environment variables in the Code section of your lambda function: CONSUMER_KEY, CONSUMER_SECRET, ACCESS_TOKEN, TOKEN_SECRET and fill their values with your twitter application keys and access tokens. Save!

Upload an image

Upload an image jpg or png to the .

Troubleshooting

If you are not seeing anything happen, got the Monitoring section of your lambda function and click on View logs in CloudWatch, this will open the CloudWatch logs for your lambda function. Select the most resent Log Stream.