# Deploying Subtrace on Fly.io

If you’re deploying your app on Fly.io, you can add Subtrace in just a couple of steps. Depending on the kind of [Fly builder](https://fly.io/docs/reference/builders) you’re using, the instructions are different. We’ll use a Python Uvicorn server as an example, but you can do this with any language and framework.

## Dockerfile Changes

Make the following changes to your app’s Dockerfile:

```
- CMD ["uvicorn", "main:app", "--host", "0.0.0.0"]
+ RUN curl -fsSLO "https://subtrace.dev/download/latest/$(uname -s)/$(uname -m)/subtrace" && chmod +x ./subtrace
+ CMD ["./subtrace", "run", "--", "uvicorn", "main:app", "--host", "0.0.0.0"]
```

Get a `SUBTRACE_TOKEN` from the **Tokens** page on the [dashboard](/content/dashboard/index.html) and set it as a Fly.io secret:

```
fly secrets set SUBTRACE_TOKEN=subt_...
```

Deploy your app as you normally would:

```
fly deploy
```

That’s it! You can now visit your app and make some requests to see them automatically appear in the Subtrace dashboard.

## Custom Buildpack

If you have a custom buildpack, add this line to its `bin/build` file to download Subtrace:

```
curl -fSLO "https://subtrace.dev/download/$(uname -s)/$(uname -m)/subtrace" && chmod +x ./subtrace
```

Change the command(s) in your `fly.toml` file to use Subtrace:

```
# fly.toml

[processes]
-   web = "uvicorn main:app --host 0.0.0.0"
+   web = "./subtrace run -- uvicorn main:app --host 0.0.0.0"
```

Get a `SUBTRACE_TOKEN` from the **Tokens** page on the [dashboard](/content/dashboard/index.html) and set it as a Fly.io secret:

```
fly secrets set SUBTRACE_TOKEN=subt_...
```

Deploy your app as you normally would:

```
fly deploy
```

That’s it! You can visit your app and make some requests to see them automatically appear in the Subtrace dashboard.