---
title: "Use environment variables"
description: "Add environment variables to a Functions function, follow the key naming rules, and read them from your code."
content_type: "how-to"
product: "functions"
platform: "MyAccount"
url: "/myaccount/functions/how-to/use-environment-variables/"
topic: ["edit"]
relationships: {"requires":["/myaccount/functions/how-to/create-a-function/"]}
---

# Use environment variables

Environment variables hold configuration, such as database URLs, service endpoints, and
application settings, separately from your function's code. You add them when you create the function or later, and your code
reads them at runtime. To change a value, change the variable and save.

## Before you begin

You need a function that is **Running** or **Failed**. Its variables are read-only while it is
**Creating** or **Deploying**. To add variables while you create a function, see
[Create a function](/myaccount/functions/how-to/create-a-function/).

## Key names

A key uses letters, digits, and underscores, and must start with a letter or underscore. It can
be up to 50 characters long. Each key must be unique within a function. Functions reserves the
name `PORT` for its own use. Choose another name. To set the port a custom container listens on,
see [Deploy a custom container image](/myaccount/functions/how-to/deploy-a-custom-container-image/).

## Add environment variables

1. In **Compute > Functions**, click the function's name to open its page.
2. Under **Function Configuration**, find **Environment variables**. If the function has no
   variables yet, click **Add Variables**.
3. Enter a **Key** and a **Value**.
4. Click **Save** to apply the change.

## Read them from code

In a Python HTTP runtime, read a variable with `os.environ`:

```python
import os

database_url = os.environ.get("DATABASE_URL")
```

In a Node.js HTTP runtime, read it with `process.env`:

```js
export const handler = async (event) => {
  const serviceUrl = process.env.SERVICE_URL;
  return { statusCode: 200, body: "ok" };
};
```

In each example, replace the variable name in `os.environ.get` or `process.env` with the key you
set.

## Check that the change applied

After you save, the function redeploys. Select the function in the Functions list and open the
**Info** tab below the list. Check that **Version** went up by one. Then call
the function to confirm it reads the new value. See
[Call a function](/myaccount/functions/how-to/call-a-function/).

If the function fails to start after you add a variable, check its logs. See
[View logs and monitoring](/myaccount/functions/how-to/view-logs-and-monitoring/) and
[Troubleshooting Functions](/myaccount/functions/troubleshooting/functions/).