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

# Variables

> A variables dictionary that defines variables to control the environment.

Optional in [single-runtime](https://developer.upsun.com/docs/configure-apps/app-reference/single-runtime-image.md#primary-application-properties) and [composable](https://developer.upsun.com/docs/configure-apps/app-reference/composable-image.md#primary-application-properties) images.

Upsun Cloud provides a number of ways to set [variables](https://developer.upsun.com/docs/development/variables).
Variables set in your app configuration have the lowest precedence,
meaning they're overridden by any conflicting values provided elsewhere.

All variables set in your app configuration must have a prefix.
Some [prefixes have specific meanings](https://developer.upsun.com/docs/development/variables#variable-prefixes).

Variables with the prefix `env` are available as a separate environment variable.
All other variables are available in
the [`PLATFORM_VARIABLES` environment variable](https://developer.upsun.com/docs/development/variables/use-variables#use-provided-variables).

The following example sets two variables:

* A variable named `env:AUTHOR` with the value `Juan` that's available in the environment as `AUTHOR`
* A variable named `d8config:system.site:name` with the value `My site rocks`
  that's available in the `PLATFORM_VARIABLES` environment variable

> [tab] Single-runtime image
>
>         applications:
>           myapp:
>             type: 'python:\{\{version:python:latest}}'
>             source:
>               root: "/"
>             variables:
>               env:
>                 AUTHOR: 'Juan'
>               d8config:
>                 "system.site:name": 'My site rocks'

> [tab] Composable image
>
>         applications:
>           myapp:
>             type: "composable:\{\{version:composable:latest}}"
>             source:
>               root: "/"
>             stack: 
>               runtimes: \[ "python@\{\{version:python:latest}}" ]
>             variables:
>               env:
>                 AUTHOR: 'Juan'
>               d8config:
>                 "system.site:name": 'My site rocks'

You can also define and access more [complex values](https://developer.upsun.com/docs/development/variables/use-variables.md#access-complex-values).


This documentation is built and hosted on [Mintlify](https://mintlify.com), a developer documentation platform.