AWS Lambda execution role - AWS Lambda

AWS Lambda execution role

A Lambda function's execution role is an AWS Identity and Access Management (IAM) role that grants the function permission to access AWS services and resources. You provide this role when you create a function, and Lambda assumes the role when your function is invoked. You can create an execution role for development that has permission to send logs to Amazon CloudWatch and to upload trace data to AWS X-Ray.

To view a function's execution role

  1. Open the Functions page on the Lambda console.

  2. Choose a function.

  3. Choose Configuration and then choose Permissions.

  4. Under Resource summary, view the services and resources that the function can access.

  5. Choose a service from the dropdown list to see permissions related to that service.

You can add or remove permissions from a function's execution role at any time, or configure your function to use a different role. Add permissions for any services that your function calls with the AWS SDK, and for services that Lambda uses to enable optional features.

When you add permissions to your function, make an update to its code or configuration as well. This forces running instances of your function, which have out-of-date credentials, to stop and be replaced.

Creating an execution role in the IAM console

By default, Lambda creates an execution role with minimal permissions when you create a function in the Lambda console. You can also create an execution role in the IAM console.

To create an execution role in the IAM console

  1. Open the Roles page in the IAM console.

  2. Choose Create role.

  3. Under Common use cases, choose Lambda.

  4. Choose Next: Permissions.

  5. Under Attach permissions policies, choose the AWS managed policies AWSLambdaBasicExecutionRole and AWSXRayDaemonWriteAccess.

  6. Choose Next: Tags.

  7. Choose Next: Review.

  8. For Role name, enter lambda-role.

  9. Choose Create role.

For detailed instructions, see Creating a role for an AWS service (console) in the IAM User Guide.

Grant least privilege access to your Lambda execution role

When you first create an IAM role for your Lambda function during the development phase, you might sometimes grant permissions beyond what is required. Before publishing your function in the production environment, best practice is to adjust the policy to include only the required permissions. For more information, see granting least privilege.

Use IAM Access Analyzer to help identify the required permissions for the IAM execution role policy. IAM Access Analyzer reviews your AWS CloudTrail logs over the date range that you specify and generates a policy template with only the permissions that the function used during that time. You can use the template to create a managed policy with fine-grained permissions, and then attach it to the IAM role. That way, you grant only the permissions that the role needs to interact with AWS resources for your specific use case.

To learn more, see Generate policies based on access activity in the IAM User Guide.

Managing roles with the IAM API

To create an execution role with the AWS Command Line Interface (AWS CLI), use the create-role command.

In the following example, you specify the trust policy inline. Requirements for escaping quotes in the JSON string vary depending on your shell.

aws iam create-role --role-name lambda-ex --assume-role-policy-document '{"Version": "2012-10-17","Statement": [{ "Effect": "Allow", "Principal": {"Service": "lambda.amazonaws.com"}, "Action": "sts:AssumeRole"}]}'

You can also define the trust policy for the role using a JSON file. In the following example, trust-policy.json is a file in the current directory. This trust policy allows Lambda to use the role's permissions by giving the service principal lambda.amazonaws.com permission to call the AWS Security Token Service AssumeRole action.

Example trust-policy.json

{ "Version": "2012-10-17", "Statement": [ { "Effect": "Allow", "Principal": { "Service": "lambda.amazonaws.com" }, "Action": "sts:AssumeRole" } ] }
aws iam create-role --role-name lambda-ex --assume-role-policy-document file://trust-policy.json

You should see the following output:

{ "Role": { "Path": "/", "RoleName": "lambda-ex", "RoleId": "AROAQFOXMPL6TZ6ITKWND", "Arn": "arn:aws:iam::123456789012:role/lambda-ex", "CreateDate": "2020-01-17T23:19:12Z", "AssumeRolePolicyDocument": { "Version": "2012-10-17", "Statement": [ { "Effect": "Allow", "Principal": { "Service": "lambda.amazonaws.com" }, "Action": "sts:AssumeRole" } ] } } }

To add permissions to the role, use the attach-policy-to-role command. Start by adding the AWSLambdaBasicExecutionRole managed policy.

aws iam attach-role-policy --role-name lambda-ex --policy-arn arn:aws:iam::aws:policy/service-role/AWSLambdaBasicExecutionRole

AWS managed policies for Lambda features

The following AWS managed policies provide permissions that are required to use Lambda features:

  • AWSLambdaBasicExecutionRole – Permission to upload logs to CloudWatch.

  • AWSLambdaDynamoDBExecutionRole – Permission to read records from an Amazon DynamoDB stream.

  • AWSLambdaKinesisExecutionRole – Permission to read events from an Amazon Kinesis data stream or consumer.

  • AWSLambdaMQExecutionRole – Permission to read records from an Amazon MQ broker.

  • AWSLambdaMSKExecutionRole – Permission to read records from an Amazon Managed Streaming for Apache Kafka (Amazon MSK) cluster.

  • AWSLambdaSQSQueueExecutionRole – Permission to read a message from an Amazon Simple Queue Service (Amazon SQS) queue.

  • AWSLambdaVPCAccessExecutionRole – Permission to manage elastic network interfaces to connect your function to a virtual private cloud (VPC).

  • AWSXRayDaemonWriteAccess – Permission to upload trace data to X-Ray.

  • CloudWatchLambdaInsightsExecutionRolePolicy – Permission to write runtime metrics to CloudWatch Lambda Insights.

  • AmazonS3ObjectLambdaExecutionRolePolicy – Permission to interact with Amazon S3 Object Lambda.

For some features, the Lambda console attempts to add missing permissions to your execution role in a customer managed policy. These policies can become numerous. To avoid creating extra policies, add the relevant AWS managed policies to your execution role before enabling features.

When you use an event source mapping to invoke your function, Lambda uses the execution role to read event data. For example, an event source mapping for Kinesis reads events from a data stream and sends them to your function in batches. You can use event source mappings with the following services:

In addition to the AWS managed policies, the Lambda console provides templates for creating a custom policy with permissions for additional use cases. When you create a function in the Lambda console, you can choose to create a new execution role with permissions from one or more templates. These templates are also applied automatically when you create a function from a blueprint, or when you configure options that require access to other services. Example templates are available in this guide's GitHub repository.