[CRCR] Add EventBridge sweeper configuration and interval variable

crcr/aws/sweeper.tf

@@ -0,0 +1,29 @@
+# Active sweeper: EventBridge fires the callback lambda on a fixed schedule so it
+# can scan the Redis ZSET of in-progress jobs and time out any "zombie" jobs whose
+# expected-timeout score has elapsed. The callback handler routes on the constant
+# payload below to branch into the cleanup logic.
+
+resource "aws_cloudwatch_event_rule" "sweeper" {
+  name                = "crcr-sweeper-${var.environment}"
+  description         = "Periodic trigger for the cross-repo-ci callback lambda to reap timed-out jobs"
+  schedule_expression = "rate(${var.sweeper_interval_minutes} minutes)"
+  tags                = local.tags
+}
+
+resource "aws_cloudwatch_event_target" "sweeper" {
+  rule      = aws_cloudwatch_event_rule.sweeper.name
+  target_id = "crcr-callback-sweeper"
+  arn       = aws_lambda_function.callback.arn
+
+  input = jsonencode({
+    source = "crcr.sweeper"
+  })
+}
+
+resource "aws_lambda_permission" "sweeper_invoke" {
+  statement_id  = "AllowEventBridgeSweeperInvoke"
+  function_name = aws_lambda_function.callback.function_name
+  action        = "lambda:InvokeFunction"
+  principal     = "events.amazonaws.com"
+  source_arn    = aws_cloudwatch_event_rule.sweeper.arn
+}

crcr/aws/variables.tf

@@ -66,3 +66,14 @@ variable "oot_status_ttl" {
   type        = number
   default     = 259200
 }
+
+variable "sweeper_interval_minutes" {
+  description = "How often EventBridge triggers the callback lambda to reap timed-out jobs (minutes)"
+  type        = number
+  default     = 10
+
+  validation {
+    condition     = var.sweeper_interval_minutes >= 2
+    error_message = "sweeper_interval_minutes must be >= 2; more frequent sweeps reap too few zombies to be worthwhile."
+  }
+}