---
title: Environment Variables
description: Runtime and user-defined environment variables available inside Container instances.
image: https://developers.cloudflare.com/dev-products-preview.png
---

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# Environment Variables

## Runtime environment variables

The container runtime automatically sets the following variables:

* `CLOUDFLARE_APPLICATION_ID` \- the ID of the Containers application
* `CLOUDFLARE_COUNTRY_A2` \- the [ISO 3166-1 Alpha 2 code ↗](https://www.iso.org/obp/ui/#search/code/) of a country the container is placed in
* `CLOUDFLARE_LOCATION` \- a name of a location the container is placed in
* `CLOUDFLARE_REGION` \- a region name
* `CLOUDFLARE_DURABLE_OBJECT_ID` \- the ID of the Durable Object instance that the container is bound to. You can use this to identify particular container instances on the dashboard.

## User-defined environment variables

You can set environment variables when defining a Container in your Worker, or when starting a container instance.

For example:

JavaScript

```

class MyContainer extends Container {

  defaultPort = 4000;

  envVars = {

    MY_CUSTOM_VAR: "value",

    ANOTHER_VAR: "another_value",

  };

}


```

More details about defining environment variables and secrets can be found in [this example](https://developers.cloudflare.com/containers/examples/env-vars-and-secrets).

```json
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```