refactor: replace samversion with sam_asset (#168)

The previous module was overly restrictive, by assuming that a caller
would always want to know only the CodeUri of a few functions. Make the
base module more generic: given an asset and a version, return the body.
The primary value the module provides is to give us a consistent default
version.

modules/forwarder/README.md

@@ -71,7 +71,7 @@ module "forwarder" {
 
 | Name | Source | Version |
 |------|--------|---------|
-| <a name="module_samversion"></a> [samversion](#module\_samversion) | ../samversion | n/a |
+| <a name="module_sam_asset"></a> [sam\_asset](#module\_sam\_asset) | ../sam_asset | n/a |
 
 ## Resources
 

modules/forwarder/main.tf

@@ -1,5 +1,5 @@
 locals {
-  code_uri        = var.code_uri != "" ? var.code_uri : module.samversion[0].code_uri
+  code_uri        = var.code_uri != "" ? var.code_uri : yamldecode(module.sam_asset[0].body)["Resources"]["Forwarder"]["Properties"]["CodeUri"]
   parsed_s3_uri   = regex("s3://(?P<bucket>[^/]+)/(?P<key>.+)", local.code_uri)
   destination_uri = var.destination.uri != "" ? var.destination.uri : "s3://${var.destination.bucket}/${var.destination.prefix}"
   name_prefix     = "${substr(var.name, 0, 37)}-"
@@ -21,10 +21,9 @@ data "aws_region" "current" {}
 
 data "aws_partition" "current" {}
 
-module "samversion" {
-  count    = var.code_uri != "" ? 0 : 1
-  source   = "../samversion"
-  app      = "forwarder"
-  function = "Forwarder"
-  release  = var.sam_release_version
+module "sam_asset" {
+  count           = var.code_uri != "" ? 0 : 1
+  source          = "../sam_asset"
+  asset           = "forwarder.yaml"
+  release_version = var.sam_release_version
 }

modules/sam_asset/README.md

@@ -0,0 +1,18 @@
+# SAM Asset
+
+This is a helper module to retrieve objects for a given release version from
+https://github.com/observeinc/aws-sam-apps.
+
+If no `release_version` is provided, we will default to a hard-coded value
+which is maintained up to date by `updatecli`. This ensures that a given
+terraform module release produces the same behavior across time.
+
+## Usage
+
+```hcl
+module "sam_asset" {
+    source          = "observeinc/collection/aws//modules/sam_asset"
+    asset           = "forwarder.yaml"
+    release_version = "1.19.3"
+}
+```

modules/samversion/main.tf → modules/sam_asset/main.tf

@@ -1,13 +1,12 @@
 locals {
-  latest_release      = "1.19.3"
-  sam_release_version = var.release != "" ? var.release : local.latest_release
-  code_uri            = yamldecode(data.http.manifest.response_body)["Resources"][var.function]["Properties"]["CodeUri"]
+  latest_release  = "1.19.3"
+  release_version = var.release_version != "" ? var.release_version : local.latest_release
 }
 
 data "aws_region" "current" {}
 
 data "http" "manifest" {
-  url = "https://observeinc-${data.aws_region.current.name}.s3.amazonaws.com/aws-sam-apps/${local.sam_release_version}/${var.app}.yaml"
+  url = "https://observeinc-${data.aws_region.current.name}.s3.amazonaws.com/aws-sam-apps/${local.release_version}/${var.asset}"
 
   lifecycle {
     postcondition {

modules/sam_asset/outputs.tf

@@ -0,0 +1,4 @@
+output "body" {
+  description = "Response body"
+  value       = data.http.manifest.response_body
+}

modules/samversion/variables.tf → modules/sam_asset/variables.tf

@@ -1,17 +1,13 @@
-variable "app" {
-  description = "App name"
+variable "asset" {
+  description = <<-EOF
+    Asset key. This value is appended to the SAM apps version prefix to form
+    the object key.
+  EOF
   type        = string
   nullable    = false
 }
 
-variable "function" {
-  description = "Function name"
-  type        = string
-  default     = ""
-  nullable    = false
-}
-
-variable "release" {
+variable "release_version" {
   description = "Release version on github.com/observeinc/aws-sam-apps."
   type        = string
   default     = ""

modules/subscriber/README.md

@@ -21,7 +21,7 @@ This app is specifically to register new cloudwatch log groups for the `logwrite
 
 | Name | Source | Version |
 |------|--------|---------|
-| <a name="module_samversion"></a> [samversion](#module\_samversion) | ../samversion | n/a |
+| <a name="module_sam_asset"></a> [sam\_asset](#module\_sam\_asset) | ../sam_asset | n/a |
 
 ## Resources
 

modules/subscriber/main.tf

@@ -2,14 +2,13 @@ locals {
   has_discovery_rate = var.discovery_rate != ""
   name_prefix        = "${substr(var.name, 0, 37)}-"
 
-  code_uri      = var.code_uri != "" ? var.code_uri : module.samversion[0].code_uri
+  code_uri      = var.code_uri != "" ? var.code_uri : yamldecode(module.sam_asset[0].body)["Resources"]["Subscriber"]["Properties"]["CodeUri"]
   parsed_s3_uri = regex("s3://(?P<bucket>[^/]+)/(?P<key>.+)", local.code_uri)
 }
 
-module "samversion" {
-  count    = var.code_uri != "" ? 0 : 1
-  source   = "../samversion"
-  app      = "logwriter"
-  function = "Subscriber"
-  release  = var.sam_release_version
+module "sam_asset" {
+  count           = var.code_uri != "" ? 0 : 1
+  source          = "../sam_asset"
+  asset           = "logwriter.yaml"
+  release_version = var.sam_release_version
 }