You can use environment variables to adjust your function's behavior without updating code. An environment variable is a pair of strings that is stored in a function's version-specific configuration. The Lambda runtime makes environment variables available to your code and sets additional environment variables that contain information about the function and invocation request.

Environment variables are not evaluated before the function invocation. Any value you define is considered a literal string and not expanded. Perform the variable evaluation in your function code.

Creating Lambda environment variables

You can configure environment variables in Lambda using the Lambda console, the AWS Command Line Interface (AWS CLI), AWS Serverless Application Model (AWS SAM), or using an AWS SDK.

Console

You define environment variables on the unpublished version of your function. When you publish a version, the environment variables are locked for that version along with otherversion-specific configuration settings.

You create an environment variable for your function by defining a key and a value. Your function uses the name of the key to retrieve the value of the environment variable.

To set environment variables in the Lambda console

1. Open theFunctions page of the Lambda console.

2. Choose a function.

3. Choose theConfiguration tab, then chooseEnvironment variables.

4. UnderEnvironment variables, chooseEdit.

5. ChooseAdd environment variable.

6. Enter a key and value.

   Requirements

   • Keys start with a letter and are at least two characters.

   • Keys only contain letters, numbers, and the underscore character (_).

   • Keys aren'treserved by Lambda.

   • The total size of all environment variables doesn't exceed 4 KB.

7. ChooseSave.

To generate a list of environment variables in the console code editor

You can generate a list of environment variables in the Lambda code editor. This is a quick way to reference your environment variables while you code.

1. Choose theCode tab.

2. Scroll down to theENVIRONMENT VARIABLES section of the code editor. Existing environment variables are listed here:

   

3. To create new environment variables, choose the choose the plus sign ():

   

Environment variables remain encrypted when listed in the console code editor. If you enabled encryption helpers for encryption in transit, then those settings remain unchanged. For more information, seeSecuring Lambda environment variables.

The environment variables list is read-only and is available only on the Lambda console. This file is not included when you download the function's .zip file archive, and you can't add environment variables by uploading this file.

AWS CLI

The following example sets two environment variables on a function namedmy-function.

aws lambda update-function-configuration \  --function-namemy-function \  --environment"Variables={BUCKET=amzn-s3-demo-bucket,KEY=file.txt}"

When you apply environment variables with theupdate-function-configuration command, the entire contents of theVariables structure is replaced. To retain existing environment variables when you add a new one, include all existing values in your request.

To get the current configuration, use theget-function-configuration command.

aws lambda get-function-configuration \  --function-namemy-function

You should see the following output:

{    "FunctionName": "my-function",    "FunctionArn": "arn:aws:lambda:us-east-2:111122223333:function:my-function",    "Runtime": "nodejs22.x",    "Role": "arn:aws:iam::111122223333:role/lambda-role",    "Environment":{        "Variables":{            "BUCKET": "amzn-s3-demo-bucket",            "KEY": "file.txt"        }    },    "RevisionId": "0894d3c1-2a3d-4d48-bf7f-abade99f3c15",    ...}

You can pass the revision ID from the output ofget-function-configuration as a parameter toupdate-function-configuration. This ensures that the values don't change between when you read the configuration and when you update it.

To configure a function's encryption key, set theKMSKeyARN option.

aws lambda update-function-configuration \  --function-namemy-function \  --kms-key-arnarn:aws:kms:us-east-2:111122223333:key/055efbb4-xmpl-4336-ba9c-538c7d31f599

AWS SAM

You can use theAWS Serverless Application Model to configure environment variables for your function. Update theEnvironment andVariables properties in yourtemplate.yaml file and then runsam deploy.

Example template.yaml

AWSTemplateFormatVersion: '2010-09-09'Transform: AWS::Serverless-2016-10-31Description: An AWS Serverless Application Model template describing your function.Resources:my-function:    Type: AWS::Serverless::Function    Properties:      CodeUri: .      Description: ''      MemorySize: 128      Timeout: 120      Handler: index.handler      Runtime: nodejs22.x      Architectures:        - x86_64      EphemeralStorage:        Size: 10240      Environment:        Variables:BUCKET: amzn-s3-demo-bucketKEY: file.txt# Other function properties...

AWS SDKs

To manage environment variables using an AWS SDK, use the following API operations.

• UpdateFunctionConfiguration

• GetFunctionConfiguration

• CreateFunction

To learn more, refer to theAWS SDK documentation for your preferred programming language.

Example scenario for environment variables

You can use environment variables to customize function behavior in your test environment and production environment. For example, you can create two functions with the same code but different configurations. One function connects to a test database, and the other connects to a production database. In this situation, you use environment variables to pass the hostname and other connection details for the database to the function.

The following example shows how to define the database host and database name as environment variables.

If you want your test environment to generate more debug information than the production environment, you could set an environment variable to configure your test environment to use more verbose logging or more detailed tracing.

For example, in your test environment, you could set an environment variable with the keyLOG_LEVEL and a value indicating a log level of debug or trace. In your Lambda function's code, you can then use this environment variable to set the log level.

The following code examples in Python and Node.js illustrate how you can achieve this. These examples assume your environment variable has a value ofDEBUG in Python ordebug in Node.js.

Python

Example Python code to set log level

import osimport logging# Initialize the loggerlogger = logging.getLogger()# Get the log level from the environment variable and default to INFO if not setlog_level = os.environ.get('LOG_LEVEL', 'INFO')# Set the log levellogger.setLevel(log_level)def lambda_handler(event, context):    # Produce some example log outputs    logger.debug('This is a log with detailed debug information - shown only in test environment')    logger.info('This is a log with standard information - shown in production and test environments')

Node.js (ES module format)

Example Node.js code to set log level

This example uses thewinston logging library. Use npm to add this library to your function's deployment package. For more information, seeCreating a .zip deployment package with dependencies.

import winston from 'winston';// Initialize the logger using the log level from environment variables, defaulting to INFO if not setconst logger = winston.createLogger({   level: process.env.LOG_LEVEL || 'info',   format: winston.format.json(),   transports: [new winston.transports.Console()]});export const handler = async (event) =>{   // Produce some example log outputs   logger.debug('This is a log with detailed debug information - shown only in test environment');   logger.info('This is a log with standard information - shown in production and test environment');   };

Retrieving Lambda environment variables

To retrieve environment variables in your function code, use the standard method for your programming language.

Node.js

let region = process.env.AWS_REGION

Python

import os  region = os.environ['AWS_REGION']

Note

In some cases, you may need to use the following format:

region = os.environ.get('AWS_REGION')

Ruby

region = ENV["AWS_REGION"]

Java

String region = System.getenv("AWS_REGION");

Go

var region = os.Getenv("AWS_REGION")

C#

string region = Environment.GetEnvironmentVariable("AWS_REGION");

PowerShell

$region = $env:AWS_REGION

Lambda stores environment variables securely by encrypting them at rest. You canconfigure Lambda to use a different encryption key, encrypt environment variable values on the client side, or set environment variables in an AWS CloudFormation template with AWS Secrets Manager.

Defined runtime environment variables

Lambdaruntimes set several environment variables during initialization. Most of the environment variables provide information about the function or runtime. The keys for these environment variables arereserved and cannot be set in your function configuration.

The following additional environment variables aren't reserved and can be extended in your function configuration.

The sample values shown reflect the latest runtimes. The presence of specific variables or their values can vary on earlier runtimes.

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