CloudFormation resources generated when AWS::Serverless::WebFunction is specified

When you specify an AWS::Serverless::WebFunction, AWS Serverless Application Model (AWS SAM) generates the following base CloudFormation resources.

AWS::Lambda::WebFunction

LogicalId: <webfunction‑LogicalId>

Referenceable property: N/A (you must use the LogicalId to reference this CloudFormation resource)

AWS::Lambda::WebFunctionRevision

LogicalId: <webfunction‑LogicalId>Revision

Referenceable property: N/A (you must use the LogicalId to reference this CloudFormation resource)

Resource attributes: UpdateReplacePolicy: Retain

Every property of a revision is create-only, so a change to the function's code or configuration replaces the revision. AWS SAM sets UpdateReplacePolicy: Retain so that CloudFormation keeps the replaced revision instead of deleting it. An endpoint can still route traffic to it through RevisionWeights, and Lambda doesn't delete a revision that an endpoint uses. The replaced revision is no longer part of the stack. Deleting the function deletes all of its revisions.

The revision created by an update that fails and rolls back is also kept.

To override this, set UpdateReplacePolicy on the AWS::Serverless::WebFunction. AWS SAM then applies your value to every resource that it generates, including the Web Function endpoint.

AWS::Lambda::WebFunctionEndpoint

LogicalId: <webfunction‑LogicalId>Endpoint

Referenceable property: N/A (you must use the LogicalId to reference this CloudFormation resource)

All three resources use the same function name. If you don't specify the FunctionName property, AWS SAM generates a name of the form <webfunction‑LogicalId>-<stack-id-prefix>, where stack-id-prefix is the first 8 characters of the stack ID's unique identifier. AWS SAM shortens the logical ID if needed so that the name is at most 64 characters.

In addition to these CloudFormation resources, when AWS::Serverless::WebFunction is specified, AWS SAM also generates CloudFormation resources for the following scenarios:

ExecutionRoleArn property is not specified

When you don't specify the ExecutionRoleArn property of an AWS::Serverless::WebFunction, AWS SAM generates an AWS::IAM::Role CloudFormation resource with the AWSLambdaBasicExecutionRole AWS managed policy attached.

The role trust policy allows the lambda.amazonaws.com service principal to assume the role.

AWS::IAM::Role

LogicalId: <webfunction‑LogicalId>Role