+++
title = "Define the HitCounter API"
weight = 100
+++

## Create a new file for our hit counter construct

Create a new file under `cdk_workshop` called `hitcounter.py` with the following content:

```python
from constructs import Construct
from aws_cdk import (
    aws_lambda as _lambda,
)

class HitCounter(Construct):

    def __init__(self, scope: Construct, id: str, downstream: _lambda.IFunction, **kwargs):
        super().__init__(scope, id, **kwargs)

        # TODO
```

Save the file.

## What's going on here?

* We declared a new construct class called `HitCounter`.
* As usual, constructor arguments are `scope`, `id` and `kwargs`, and we
  propagate them to the `cdk.Construct` base class.
* The `HitCounter` class also takes one explicit keyword parameter `downstream`
  of type `lambda.IFunction`. This is where we are going to "plug in" the Lambda
  function we created in the previous chapter so it can be hit-counted.

----

Next, are are going to write the handler code of our hit counter.