> ## Documentation Index
> Fetch the complete documentation index at: https://docs.metlo.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Node

### Installation

Currently Metlo's Node Agent supports 3 frameworks:

* Express
* Koa
* Fastify

It can be installed from `npm` by running:

```bash Bash theme={null}
npm install metlo
```

Or from `yarn` by running:

```bash Bash theme={null}
yarn add metlo
```

### Configuration

#### Express

Metlo can be included as a standard Express Middleware.

```js theme={null}
import { initExpress as metlo } from "metlo";
// Or using require
const metlo = require("metlo").initExpress;
...
const app = express();
...
app.use(
  metlo(
    {
      key: <YOUR_METLO_API_KEY>,
      host: "http://<YOUR_METLO_HOST>:8081",
    }
  )
);
```

#### Koa

Metlo can be included as a standard Koa Middleware.

```js theme={null}
import { initKoa as metlo } from "metlo";
// Or using require
const metlo = require("metlo").initKoa;
...
const app = new Koa();
...
app.use(
  metlo(
    {
      key: <YOUR_METLO_API_KEY>,
      host: "http://<YOUR_METLO_HOST>:8081",
    }
  )
);
```

#### Fastify

Metlo can be included as a standard Fastify plugin.

```js theme={null}
import { initFastify as metlo } from "metlo";
// Or using require
const metlo = require("metlo").initFastify;
...
const fastify = Fastify();
...
fastify.register(
  metlo(
    {
      key: <YOUR_METLO_API_KEY>,
      host: "http://<YOUR_METLO_HOST>:8081",
    }
  )
);
```

#### Extra configuration

Metlo for NodeJS can further be customized to add more context to collected traces or to enable/disable functionality.

* host : Location of the Metlo instance
* key : API key used for collecting to Metlo
* backendPort : Backend port used by Metlo.
* collectorPort : Collector port used to capture traces. Defaults to 8081
* logLevel : The log level Metlo should log at. Can be
  * trace
  * info
  * debug
  * warn
  * error
* getUser : A function that takes in a request/response or context and returns the user for that request. By default, Metlo collects no information about user of a request.
* rejectResponse : Response to return when Metlo is set to block malicious requests.
* maxBodyCaptureSize : Max size of request/response bodies that Metlo should capture. Defaults to 5 KB
* disableBlocking : Used to disable request blocking by Metlo.

In addition, Metlo accepts two environment variables

* METLO\_DISABLE\_BLOCKING : If provided a truthy value (true, 1, yes), then will disable request blocking by Metlo. Defaults to false.
* METLO\_ENABLE : If **left unset** or provided a truthy value (true, 1, yes), then will enable Metlo. Conversely, providing a value other than that listed above would disable Metlo. Defaults to true