Merge pull request #7 from AndrewFarley/allow-existing-sns

Feature: Allow existing SNS via a variable flag

Author: dubiety

.gitignore

@@ -7,3 +7,7 @@
 
 # .tfvars files
 *.tfvars
+
+# Build harness
+.build-harness
+build-harness/

README.md

@@ -56,6 +56,17 @@ module "es_alarms" {
 }
 ```
 
+You can alternatively have this module not create an SNS incase you have existing ones created elsewhere.
+
+```hcl
+module "es_alarms" {
+  source           = "github::https://github.com/dubiety/terraform-aws-elasticsearch-cloudwatch-sns-alarms.git?ref=master"
+  domain_name      = "example"
+  sns_topic        = "arn:aws:sns:us-east-1:123456123456:sns-to-slack"   # < Put your full SNS ARN here, if necessary read from var or a resource
+  create_sns_topic = false
+}
+```
+
 
 ## Inputs
 
@@ -80,7 +91,8 @@ module "es_alarms" {
 | `monitor_jvm_memory_pressure_too_high` | Enable monitoring of JVM memory pressure is too high | string | `true` | no |
 | `monitor_master_cpu_utilization_too_high` | Enable monitoring of CPU utilization of master nodes are too high. Only enable this when dedicated master is enabled | string | `false` | no |
 | `monitor_master_jvm_memory_pressure_too_high` | Enable monitoring of JVM memory pressure of master nodes are too high. Only enable this wwhen dedicated master is enabled | string | `false` | no |
-| `sns_topic` | SNS topic you want to specify. If leave empty, it will use a prefix and a timestampe appended | string | `""` | no |
+| `create_sns_topic` | Will create an SNS topic, if you set this to false you MUST set `sns_topic` to a FULL ARN | string | `true` | no |
+| `sns_topic` | SNS topic you want to specify. If leave empty, it will use a prefix and a timestamp appended.  If `create_sns_topic` is set to false, this MUST be a FULL ARN | string | `""` | no |
 | `sns_topic_postfix` | SNS topic postfix | string | `""` | no |
 | `sns_topic_prefix` | SNS topic prefix | string | `""` | no |
 

examples/use-existing-sns/main.tf

@@ -0,0 +1,33 @@
+### For connecting and provisioning
+variable "region" {
+  default = "us-west-2"
+}
+
+provider "aws" {
+  region = var.region
+
+  # Make it faster by skipping something
+  skip_get_ec2_platforms      = true
+  skip_metadata_api_check     = true
+  skip_region_validation      = true
+  skip_credentials_validation = true
+  skip_requesting_account_id  = true
+}
+
+# Create an existing SNS topic (aka, do not create in module)
+resource "aws_sns_topic" "this" {
+  name  = "using-existing-sns-topic-test"
+}
+
+module "es_alarms" {
+  source              = "../../"
+  domain_name         = "example"
+  # To use an existing SNS topic, your sns_topic MUST be a full ARN
+  sns_topic           = var.aws_sns_topic.arn
+  # And you must set this to false
+  create_sns_topic    = false
+}
+
+output "es_alarms_sns_topic_arn" {
+  value = module.es_alarms.sns_topic_arn
+}

main.tf

@@ -6,26 +6,44 @@ data "aws_caller_identity" "default" {}
 
 # Make a topic
 resource "aws_sns_topic" "default_prefix" {
-  count       = var.sns_topic == "" ? 1 : 0
+  count       = var.sns_topic == "" && var.create_sns_topic == true ? 1 : 0
   name_prefix = "${var.sns_topic_prefix}elasticsearch-threshold-alerts${var.sns_topic_postfix}"
 }
 
 resource "aws_sns_topic" "default" {
-  count = var.sns_topic != "" ? 1 : 0
+  count = var.sns_topic != "" && var.create_sns_topic == true ? 1 : 0
   name  = "${var.sns_topic_prefix}${var.sns_topic}${var.sns_topic_postfix}"
 }
 
 locals {
-  aws_sns_topic_arn  = var.sns_topic == "" ? element(concat(aws_sns_topic.default_prefix.*.arn, list("")), 0) : element(concat(aws_sns_topic.default.*.arn, list("")), 0)
-  aws_sns_topic_name = var.sns_topic == "" ? element(concat(aws_sns_topic.default_prefix.*.name, list("")), 0) : var.sns_topic
+  aws_sns_topic_arn = coalesce(
+    element(
+      concat(
+        aws_sns_topic.default_prefix.*.arn,
+        [""],
+      ),
+      0,
+    ),
+    element(
+      concat(
+        aws_sns_topic.default.*.arn,
+        [""],
+      ),
+      0,
+    ),
+    var.sns_topic
+  )
+  aws_sns_topic_name = element(split(":", local.aws_sns_topic_arn), 5)
 }
 
 resource "aws_sns_topic_policy" "default" {
+  count  = var.create_sns_topic == true ? 1 : 0
   arn    = local.aws_sns_topic_arn
-  policy = data.aws_iam_policy_document.sns_topic_policy.json
+  policy = data.aws_iam_policy_document.sns_topic_policy[0].json
 }
 
 data "aws_iam_policy_document" "sns_topic_policy" {
+  count     = var.create_sns_topic == true ? 1 : 0
   policy_id = "__default_policy_ID"
 
   statement {

variables.tf

@@ -3,6 +3,12 @@ variable "domain_name" {
   type        = string
 }
 
+variable "create_sns_topic" {
+  description = "If you don't want to create the SNS topic, set this to false.  It will use the sns_topic value directly"
+  type        = bool
+  default     = true
+}
+
 variable "sns_topic" {
   description = "SNS topic you want to specify. If leave empty, it will use a prefix and a timestampe appended"
   type        = string