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DVA-C02 · Question #245

A developer registered an AWS Lambda function as a target for an Application Load Balancer (ALB) using a CLI command. However, the Lambda function is not being invoked when the client sends requests…

The correct answer is C. The permissions to invoke the Lambda function are missing. When a Lambda function is registered as an ALB target via CLI, the ALB must be explicitly granted permission to invoke it via a resource-based policy. Without this permission, requests through the ALB will fail silently.

Submitted by mike_84· Mar 5, 2026Troubleshooting and Optimization

Question

A developer registered an AWS Lambda function as a target for an Application Load Balancer (ALB) using a CLI command. However, the Lambda function is not being invoked when the client sends requests through the ALB. Why is the Lambda function not being invoked?

Options

  • AA Lambda function cannot be registered as a target for an ALB.
  • BA Lambda function can be registered with an ALB using AWS Management Console only.
  • CThe permissions to invoke the Lambda function are missing.
  • DCross-zone is not enabled on the ALB.

How the community answered

(53 responses)
  • A
    2% (1)
  • B
    6% (3)
  • C
    89% (47)
  • D
    4% (2)

Why each option

When a Lambda function is registered as an ALB target via CLI, the ALB must be explicitly granted permission to invoke it via a resource-based policy. Without this permission, requests through the ALB will fail silently.

AA Lambda function cannot be registered as a target for an ALB.

Lambda functions can be registered as ALB targets; this is a supported integration since 2018.

BA Lambda function can be registered with an ALB using AWS Management Console only.

Lambda targets can be registered with an ALB using the CLI, SDKs, or CloudFormation, not just the console.

CThe permissions to invoke the Lambda function are missing.Correct

Registering a Lambda function as an ALB target does not automatically grant the ALB invoke permissions. A resource-based policy must be added to the Lambda function using `lambda:AddPermission` with the ALB as the principal. Without this explicit permission, the ALB cannot invoke the function, even if it is correctly registered as a target.

DCross-zone is not enabled on the ALB.

Cross-zone load balancing distributes traffic across Availability Zones and has no bearing on whether a Lambda function can be invoked.

Concept tested: Lambda resource-based policy for ALB invocation

Source: https://docs.aws.amazon.com/lambda/latest/dg/services-alb.html

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