VPC Lambda functions should operate in multiple Availability Zones

How to fix it

In the console

Lambda → Functions → the function → Configuration → VPC

Subnets

The subnets attached now plus at least one in another Availability Zone

Aliases

Publish a new version and point each alias at it; published versions keep the old subnets

With the AWS CLI

• Overwrites existing settings: The --vpc-config value replaces the function's subnet and security group lists, so pass every subnet and security group the function keeps.

aws lambda update-function-configuration --function-name <function-name> --vpc-config SubnetIds=<subnet-id-in-zone-a>,<subnet-id-in-zone-b>,SecurityGroupIds=<security-group-id> --region <region>

With Terraform

resource "aws_lambda_function" "this" {
  function_name = var.function_name
  role          = var.execution_role_arn
  filename      = var.deployment_package

  vpc_config {
    subnet_ids         = [var.subnet_id_zone_a, var.subnet_id_zone_b]
    security_group_ids = var.security_group_ids
  }
}