Why isn't my Event Bridge rule executing my Lambda function? - amazon-web-services

Question

I am trying to create an Event Bridge rule that will run my Lambda function every 30 mins.
I based my code on this answer I found here on SO Use terraform to set up a lambda function triggered by a scheduled event source
Here is my terraform code:
monitoring/main.tf:
...
module "cloudwatch_event_rule" {
source = "./cloudwatch_event_rule"
extra_tags = local.extra_tags
}
module "lambda_function" {
source = "./lambda_functions"
extra_tags = local.extra_tags
alb_names = var.alb_names
slack_webhook_url = var.slack_webhook_url
environment_tag = local.environment_tag
}
module "cloudwatch_event_target" {
source = "./cloudwatch_event_target"
lambda_function_arn = module.lambda_function.detect_bad_rejects_on_alb_lambda_arn
cloudwatch_event_rule_name = module.cloudwatch_event_rule.cloudwatch_event_rule_name
extra_tags = local.extra_tags
}
monitoring/lambda_functions/main.tf:
resource "aws_lambda_function" "detect_bad_rejects_on_alb" {
filename = var.filename
function_name = var.function_name
role = aws_iam_role.detect_bad_reject_on_alb.arn
handler = var.handler
source_code_hash = filebase64sha256(var.filename)
runtime = var.runtime
timeout = var.timeout
environment {
...
}
}
monitoring/cloudwatch_event_rule/main.tf
resource "aws_cloudwatch_event_rule" "event_rule" {
name = var.rule_name
description = var.description
schedule_expression = var.schedule_expression
tags = ...
}
monitoring/cloudwatch_event_rule/variables.tf
...
variable "schedule_expression" {
type = string
default = "rate(30 minutes)"
}
...
monitoring/cloudwatch_event_target/main.tf
resource "aws_cloudwatch_event_target" "event_target" {
arn = var.lambda_function_arn
rule = var.cloudwatch_event_rule_name
input = var.input
}
This ends up creating the lambda function and the event bridge rule with my lambda function as its target with the schedule expression "rate(30 minutes)" but the lambda function is never executed? What am I doing wrong?

Answer 1

From what you posted is seems that you are not adding permissions for invocations. Your code does not show creation of aws_lambda_permission with proper rules. So you should add such permissions so that EventBridge can invoke your function (example):
resource "aws_lambda_permission" "event-invoke" {
statement_id = "AllowExecutionFromCloudWatch"
action = "lambda:InvokeFunction"
function_name = var.function_name
principal = "events.amazonaws.com"
source_arn = module.cloudwatch_event_rule.cloudwatch_event_rule_arn
}
Make sure source_arn correctly points to the ARN of your event rule.