Support optional externally managed cloudwatch log group (#66)

main.tf

@@ -7,6 +7,7 @@ data "aws_region" "current" {}
 # Cloudwatch
 # ------------------------------------------------------------------------------
 resource "aws_cloudwatch_log_group" "main" {
+  count             = var.log_group_name != "" ? 0 : 1
   name              = var.name_prefix
   retention_in_days = var.log_retention_in_days
   tags              = var.tags
@@ -51,6 +52,7 @@ resource "aws_iam_role" "task" {
 }
 
 resource "aws_iam_role_policy" "log_agent" {
+  count  = var.log_group_name != "" ? 0 : 1
   name   = "${var.name_prefix}-log-permissions"
   role   = aws_iam_role.task.id
   policy = data.aws_iam_policy_document.task_permissions.json
@@ -140,7 +142,7 @@ locals {
   task_container_mount_points  = concat([for v in var.efs_volumes : { containerPath = v.mount_point, readOnly = v.readOnly, sourceVolume = v.name }], var.mount_points)
 
   log_configuration_options = merge({
-    "awslogs-group"         = aws_cloudwatch_log_group.main.name
+    "awslogs-group"         = var.log_group_name != "" ? var.log_group_name : aws_cloudwatch_log_group.main.0.name,
     "awslogs-region"        = data.aws_region.current.name
     "awslogs-stream-prefix" = "container"
   }, local.log_multiline_pattern)

outputs.tf

@@ -48,7 +48,7 @@ output "service_name" {
 
 output "log_group_name" {
   description = "The name of the Cloudwatch log group for the task."
-  value       = aws_cloudwatch_log_group.main.name
+  value       = var.log_group_name != "" ? var.log_group_name : aws_cloudwatch_log_group.main.0.name
 }
 
 output "desired_count" {

policies.tf

@@ -16,9 +16,9 @@ data "aws_iam_policy_document" "task_permissions" {
   statement {
     effect = "Allow"
 
-    resources = [
-      "${aws_cloudwatch_log_group.main.arn}:*",
-    ]
+    resources = compact([
+      "${var.log_group_name != "" ? "" : aws_cloudwatch_log_group.main.0.arn}:*",
+    ])
 
     actions = [
       "logs:CreateLogStream",

variables.tf

@@ -108,6 +108,12 @@ variable "task_container_environment" {
   type        = map(string)
 }
 
+variable "log_group_name" {
+  description = "The name of the provided CloudWatch Logs log group to use."
+  default     = ""
+  type        = string
+}
+
 variable "log_retention_in_days" {
   description = "Number of days the logs will be retained in CloudWatch."
   default     = 30