Is it possible to add a file to my app? Or is there another way to add a secret API key?

As far as adding a file, you could configure a custom build command to pull down a file during the build process. Outside of that we don’t have any other mechanisms to add an “env” file.

You can however, define a given environment variable as a secret for your application. We store the value encrypted along the entire process until it gets mounted in your container for use.

It’s both available as an option when configuring environment variables in the UI as well as on the app spec.

Here is how you would set it in an example app spec:

name: sample-environment-app-types
services:
- name: web
  ...
  envs:
  - key: TYPE_SECRET
    type: SECRET
    value: secret-value

Note: After submitting, value will always be returned as an encrypted value in your app spec. You can keep re-submitting the encrypted value to leave it unchanged, or specify another plain text value to update it.

Additionally, feel free to reference our spec documentation for more information about all the configuration options available to you:

https://www.digitalocean.com/docs/app-platform/references/app-specification-reference/