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

## Create a new file for our hit counter construct

Create a new file under `src/CdkWorkshop` called `HitCounter.cs` with the following content:

```csharp
using Amazon.CDK;
using Amazon.CDK.AWS.Lambda;
using Constructs;

namespace CdkWorkshop
{
    public class HitCounterProps
    {
        // The function for which we want to count url hits
        public IFunction Downstream { get; set; }
    }

    public class HitCounter : Construct
    {
        public HitCounter(Construct scope, string id, HitCounterProps props) : base(scope, id)
        {
            // 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 `props`, and we
  propagate them to the `Construct` base class.
* The `props` argument is of type `HitCounterProps` which includes a single
  property `Downstream` of type `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, we are going to write the handler code of our hit counter.