# Configuring Environment Variables

Environment variables are key-value pairs that are stored outside of source
code. The values of environment variables can be applied to particular
environments in order to change behavior or configuration.

Environment variables can be read into source code and many configuration files
in your project. Variables are only applied to environments on new deployments.
If you change an environment variable, you must redeploy the environment in
order for the updated value to take effect.

Environment variables can be configuration or secrets. While all values are
stored encrypted at rest, only non-secret values can be read. Secrets are
write-only, meaning the value can't be retrieved once it's set.

:::tip

API Reference For detailed information about accessing environment variables in
code, see the
[Environment Variables API Reference](../programmable-api/environment.mdx).

:::

## Environment Variable Editor

To set environment variables in your project, click **Settings** and then select
**Environment Variables**.

To create a new variable, click **Add new variable**.

![Adding a new environment variable](../../public/media/environment-variables/bec84962-0139-4371-b3fd-a30e70860169.png)

Enter the name and value of your environment variable and select if you would
like the value to be a secret or a regular value.

## Environments

Environment variables can be applied to one or many different environments. You
can select one or more environments in which to apply the variable.

| Environment                | Description                                                                                                                                                                                    |
| -------------------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| Prod                       | The environment that's deployed from your **default** branch in source control. This is usually called `main`.                                                                                 |
| Preview                    | Any environment that's deployed from source control that's **not the default** branch. (for example `staging` or `preview`). This also includes any branch that's created from a pull request. |
| Development (Working Copy) | Any environment that's deployed while developing with the portal. Each developer gets their own development environment. These environments are always deployed to `zuplo.dev`                 |

For the **Preview** environment option, a specific named environment can be
selected. For example, if you want a variable set only for the environment
deployed from the `staging` branch in source control.

For the **Working Copy** option, developers can set a personal override. This
value **ONLY** applies to the developer who set the value.

:::info

A single environment variable name can't overlap environments. For example, if
you set a variable named `MY_VAR` and select all the environments a second
variable named `MY_VAR` can't be set on say the **Production** environments.

:::

## Reserved Environment Variables

Environment variables can't start with `ZUPLO` or `__ZUPLO`.

## Using Environment Variables

Environment variables can be used in several places within your Zuplo project:

### In Code

Variables are accessed through the `environment` object from `@zuplo/runtime`.
See the
[Environment Variables API Reference](../programmable-api/environment.mdx) for
detailed usage examples and patterns.

### In Configuration Files

Inside some configuration files, environment variables can be referenced with
the pattern `$env(MY_VAR)`.

For example, in the `policies.json` file, an environment variable could be set
on a policy option.

```json
{
  "name": "my-custom-code-inbound-policy",
  "policyType": "custom-code-inbound",
  "handler": {
    "export": "default",
    "module": "$import(./modules/YOUR_MODULE)",
    "options": {
      "config1": "$env(MY_CONFIG_VAR)",
      "config2": true
    }
  }
}
```

### Rewrite & Forwarding Handler

When referencing environment variables inside of the URL Rewrite handler and the
URL Forward handler, variables are substituted using JavaScript style string
interpolation.

```txt
https://${env.API_URL}/path/to/call
```

## System Environment Variables

The following variables are automatically set by the system and are available to
use in your code:

- `ZUPLO_ENVIRONMENT_TYPE` - The current environment type the API is running.
  Values are `edge`, `local`.
- `ZUPLO_ENVIRONMENT_STAGE` - The stage of the environment. Values are
  `production`, `preview`, `working-copy`, and `local`.
- `ZUPLO_ENVIRONMENT_NAME` - The name of the environment. This is a globally
  unique name for the environment. This is the same name that's used in the URL
  of the environment. For example, `my-project-main-1235.zuplo.app`. Setting a
  custom domain on the environment won't change this value.
- `ZUPLO_ACCOUNT_NAME` - The name of the Zuplo account where the environment is
  deployed.
- `ZUPLO_PROJECT_NAME` - The name of the project where the environment is
  deployed.
- `ZUPLO_BUILD_ID` - The build ID of the environment. This is a unique ID for
  each build of the environment. This is a UUID.
- `ZUPLO_COMPATIBILITY_DATE` - The
  [compatibility date](../programmable-api/compatibility-dates.mdx) of runtime
  environment.