What?

This is a Lambda function that, when installed, offers you a HTTP service with which you can increment DynamoDB-backed counters. Use case is to generate sequential unique IDs (1, 2, 3, ...). There are still times when you just can't use a UUID, and you need this service to be reliable and available - hence ran on AWS.

Why?

Our use case was to implement globally unique tenant IDs for a multi-tenanted application that for space saving purpose shall remain a (relatively small) integer instead of a UUID. Most of our architecture is eventually consistent, so we cannot generate atomic sequential IDs for the few entities that need them and that's what this service is for.

How?

$ curl -X POST https://REDACTED.execute-api.us-east-1.amazonaws.com/prod/counter/increment?counter=mycounter
{
	"counter": "mycounter",
	"new_value": 714
}

The REDACTED part you'll find out after you install this package to your AWS account.

Download

Master release is always available from S3 as master.zip, published automatically from the CI server.

Credits

• This project is built on the work of serg-io/dynamodb-atomic-counter, thanks!

Install

Step 1: Create DynamoDB table:

• Go to AWS > DynamoDB > Tables > Create
• Table name = AtomicCounters
• Primary key = id (type string)
• [ Create ]

Step 2: Create IAM role:

• Go to AWS > IAM > Roles > Create new role
• Role name = AtomicCounter
• Role type = AWS Service Roles > AWS Lambda
• Do not attach any policies, but click [ Next ] and [ Create role ]

Now, AWS > IAM > Roles > AtomicCounter > Inline policies > Custom policy:

• Name = dynamodb-atomiccounters

Content:

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "",
            "Effect": "Allow",
            "Action": [
                "dynamodb:UpdateItem"
            ],
            "Resource": [
                "arn:aws:dynamodb:*:*:table/AtomicCounters"
            ]
        },
        {
            "Sid": "",
            "Resource": "*",
            "Action": [
                "logs:CreateLogGroup",
                "logs:CreateLogStream",
                "logs:PutLogEvents"
            ],
            "Effect": "Allow"
        }
    ]
}

Step 3: Create Lambda function:

• Go to AWS > Lambda > Create
• Use blank function as a template - we'll overwrite it soon
• Do not add any triggers - just hit [ Next ]
• Name = AtomicCounter
• Runtime = Node.js 4.3
• Code entry type = Upload a .ZIP file
• Download this zip file to your desktop, and then upload to Lambda
• Role = Choose an existing role
• Existing role = AtomicCounter
• Timeout = 15 sec
• [ Create function ]

Step 4: Create API Gateway:

• Go to AWS > API Gateway > Create API > New API
• Name = AtomicCounter
• [ Create API ]

Now in Actions > Create resource:

• Configure as proxy resource = check
• Resource name = proxy
• Resource path = {proxy+}
• [ Create resource ]
• Integration type = Lambda function proxy
• Lambda region = the region of your Lambda function
• Lambda function = AtomicCounter
• [ Save ]

And then Actions > Deploy API:

• Deployment stage = prod (or new stage + stage name = prod if not exists)

Now you should see the Invoke URL: https://m2toimgsc8.execute-api.us-east-1.amazonaws.com/prod.

The m2toimgsc8 part is your API ID, which you would use in place of REDACTED from the usage example.

That's it!

Support / contact

Basic support (no guarantees) for issues / feature requests via GitHub issues.

Paid support is available via function61.com/consulting

Contact options (email, Twitter etc.) at function61.com