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Merged
merged 2 commits into from
Aug 29, 2025
Merged

feat: add VPC and subnet name support #54

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2c0ec7b
feat: allow passing VPC and Subnet names
gberenice Aug 28, 2025
21f6285
chore: security best-practices + minor improvements
gberenice Aug 29, 2025
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92 changes: 91 additions & 1 deletion data.tf
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Original file line number Diff line number Diff line change
@@ -1,6 +1,30 @@
data "aws_region" "current" {}
data "aws_caller_identity" "current" {}

# VPC lookup by name (when vpc_name is provided)
data "aws_vpc" "selected" {
count = var.vpc_name != null ? 1 : 0

filter {
name = "tag:Name"
values = [var.vpc_name]
}
}

# Individual subnet lookup by name (when subnet_names are provided)
data "aws_subnet" "selected" {
for_each = toset(var.subnet_names)

filter {
name = "tag:Name"
values = [each.value]
}
filter {
name = "vpc-id"
values = [local.vpc_id]
}
}

# Most recent Amazon Linux 2023 AMI
data "aws_ami" "amazon_linux_2023" {
most_recent = true
Expand Down Expand Up @@ -33,7 +57,7 @@ data "aws_ami" "amazon_linux_2023" {
# This rule was introduced in the following PR:
# https://github.com/masterpointio/terraform-aws-ssm-agent/pull/43.
#
# trunk-ignore(trivy/AVD-AWS-0344)
# trivy:ignore:AVD-AWS-0344
data "aws_ami" "instance" {
count = length(var.ami) > 0 ? 1 : 0

Expand All @@ -44,3 +68,69 @@ data "aws_ami" "instance" {
values = [var.ami]
}
}

# IAM policy document for EC2 instances to assume the SSM Agent role
data "aws_iam_policy_document" "default" {

statement {
effect = "Allow"
actions = ["sts:AssumeRole"]

principals {
type = "Service"
identifiers = ["ec2.amazonaws.com"]
}
}
}

# https://docs.aws.amazon.com/systems-manager/latest/userguide/getting-started-create-iam-instance-profile.html#create-iam-instance-profile-ssn-logging
data "aws_iam_policy_document" "session_logging" {
count = var.session_logging_enabled ? 1 : 0

statement {
sid = "SSMAgentSessionAllowS3Logging"
effect = "Allow"
actions = [
"s3:PutObject"
]
resources = ["${local.session_logging_bucket_arn}/*"]
}

statement {
sid = "SSMAgentSessionAllowCloudWatchLogging"
effect = "Allow"
actions = [
"logs:CreateLogStream",
"logs:PutLogEvents"
]
resources = ["${local.session_logging_log_group_arn}:*"]
}

statement {
sid = "SSMAgentSessionAllowCloudWatchDescribe"
effect = "Allow"
actions = [
"logs:DescribeLogGroups",
"logs:DescribeLogStreams"
]
resources = [local.session_logging_log_group_arn]
}

statement {
sid = "SSMAgentSessionAllowGetEncryptionConfig"
effect = "Allow"
actions = [
"s3:GetEncryptionConfiguration"
]
resources = [local.session_logging_bucket_arn]
}

statement {
sid = "SSMAgentSessionAllowKMSDataKey"
effect = "Allow"
actions = [
"kms:GenerateDataKey"
]
resources = [local.session_logging_kms_key_arn]
}
}
75 changes: 75 additions & 0 deletions examples/with-names/main.tf
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Original file line number Diff line number Diff line change
@@ -0,0 +1,75 @@
provider "aws" {
region = var.region
}

# Create VPC and subnets with specific names for demonstration
module "vpc" {
source = "cloudposse/vpc/aws"
version = "2.1.0"

namespace = var.namespace
stage = var.stage
name = "example-vpc"

ipv4_primary_cidr_block = "10.0.0.0/16"
assign_generated_ipv6_cidr_block = true
}

module "subnets" {
source = "cloudposse/dynamic-subnets/aws"
version = "2.3.0"
namespace = var.namespace
stage = var.stage
name = "example-subnets"

availability_zones = var.availability_zones
vpc_id = module.vpc.vpc_id
igw_id = [module.vpc.igw_id]
ipv4_cidr_block = [module.vpc.vpc_cidr_block]
ipv6_enabled = var.ipv6_enabled
}

# Example 1: Using VPC and subnet IDs (traditional approach)
module "ssm_agent_with_ids" {
source = "../../"
stage = var.stage
namespace = var.namespace
name = "ssm-with-ids"

vpc_id = module.vpc.vpc_id
subnet_ids = module.subnets.private_subnet_ids
}

# Example 2: Using VPC and subnet names (new functionality)
module "ssm_agent_with_names" {
source = "../../"
stage = var.stage
namespace = var.namespace
name = "ssm-with-names"

vpc_name = module.vpc.vpc_id_tag_name # This would be the Name tag value
subnet_names = [
# These would be the actual Name tag values of the subnets
# In a real scenario, you'd know these names or get them from data sources
"example-private-subnet-1",
"example-private-subnet-2"
]

depends_on = [module.subnets]
}
Comment on lines +58 to +59
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@coderabbitai coderabbitai bot Aug 28, 2025

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💡 Verification agent

❓ Verification inconclusive

depends_on here won’t fix plan-time data lookups

Data sources inside the child module resolve during planning; they won’t “wait” for module.subnets. This example will often fail on first plan/apply when the subnets don’t yet exist. Document this limitation or prefer IDs when creating the subnets in the same run.

-  depends_on = [module.subnets]
+  # Note: Name-based lookups plan-time resolve and can fail on first apply if subnets are created in the same run.
+  # Consider using IDs when creating subnets, or run in two stages (create subnets, then apply this module with names).

Document plan-time data lookup limitation and prefer IDs or two-stage applies
Terraform data sources inside modules resolve during the planning phase, so a depends_on on module.subnets won’t delay those lookups until after subnet creation—this can cause failures on the first apply when subnets don’t yet exist. Update the example to either:

  • Use subnet IDs directly in this module (so the lookup happens against created resources)
  • Or split into two runs: first apply the subnets module, then apply the module relying on name-based lookups.
🤖 Prompt for AI Agents 
In examples/with-names/main.tf around lines 58-59, the current depends_on =
[module.subnets] comment is misleading because Terraform data sources inside
modules are evaluated at plan time and won’t wait for the subnets to be created;
update the example to either (A) accept and pass the subnet IDs into this module
so the module uses explicit IDs (avoiding plan-time lookups), or (B) document
and demonstrate a two-stage apply workflow (first terraform apply for the
subnets module, then apply for the dependent module) and remove/clarify the
depends_on that implies data lookups will be delayed until after creation.


# Example 3: Mixed configuration (VPC by ID, subnets by name)
module "ssm_agent_mixed" {
source = "../../"
stage = var.stage
namespace = var.namespace
name = "ssm-mixed"

vpc_id = module.vpc.vpc_id
subnet_names = [
"example-private-subnet-1",
"example-private-subnet-2"
]

depends_on = [module.subnets]
}
Comment on lines +74 to +75
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🛠️ Refactor suggestion

Same plan-time lookup caveat for mixed example

Remove depends_on and add a note, or switch the example to consume existing infra names.

-  depends_on = [module.subnets]
+  # See note above regarding plan-time name lookups when subnets are created in the same run.
📝 Committable suggestion

‼️ IMPORTANT
Carefully review the code before committing. Ensure that it accurately replaces the highlighted code, contains no missing lines, and has no issues with indentation. Thoroughly test & benchmark the code to ensure it meets the requirements.

Suggested change
depends_on = [module.subnets]
}
# See note above regarding plan-time name lookups when subnets are created in the same run.
}
🤖 Prompt for AI Agents 
In examples/with-names/main.tf around lines 74-75, the explicit depends_on =
[module.subnets] introduces a plan-time lookup caveat; remove the depends_on
line and either (a) add a short comment/note in the example explaining the
caveat and recommending consuming named existing infra (or using data sources)
instead of forcing depends_on, or (b) modify the example to consume existing
infra names/IDs (e.g., accept variables or use data sources for subnets) so the
example no longer needs depends_on. Ensure the file reflects the chosen approach
and update any adjacent README/example text to explain the behavior.

23 changes: 23 additions & 0 deletions examples/with-names/variables.tf
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@@ -0,0 +1,23 @@
variable "region" {
type = string
description = "AWS region"
default = "us-east-1"
}

variable "namespace" {
type = string
description = "Namespace for resource naming"
default = "mp"
}

variable "stage" {
type = string
description = "Stage for resource naming"
default = "test"
}

variable "availability_zones" {
type = list(string)
description = "List of availability zones"
default = ["us-east-1a", "us-east-1b"]
}
93 changes: 17 additions & 76 deletions main.tf
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Expand Up @@ -14,6 +14,10 @@ locals {
length(var.ami) > 0 ? element(data.aws_ami.instance, 0).root_device_name : "/dev/xvda"
)

# VPC and Subnet ID resolution - names take precedence over IDs
vpc_id = var.vpc_name != null ? one(data.aws_vpc.selected[*].id) : var.vpc_id
subnet_ids = length(var.subnet_names) > 0 ? values(data.aws_subnet.selected)[*].id : var.subnet_ids

}

resource "null_resource" "validate_instance_type" {
Expand All @@ -27,6 +31,7 @@ resource "null_resource" "validate_instance_type" {
}
}


module "role_label" {
source = "cloudposse/label/null"
version = "0.25.0"
Expand All @@ -47,8 +52,10 @@ locals {
region = coalesce(var.region, data.aws_region.current.region)
account_id = data.aws_caller_identity.current.account_id

session_logging_bucket_name = try(coalesce(var.session_logging_bucket_name, module.logs_label.id), "")
session_logging_kms_key_arn = try(coalesce(var.session_logging_kms_key_arn, module.kms_key.key_arn), "")
session_logging_bucket_name = try(coalesce(var.session_logging_bucket_name, module.logs_label.id), "")
session_logging_kms_key_arn = try(coalesce(var.session_logging_kms_key_arn, module.kms_key.key_arn), "")
session_logging_bucket_arn = var.session_logging_enabled ? "arn:aws:s3:::${local.session_logging_bucket_name}" : ""
session_logging_log_group_arn = var.session_logging_enabled ? "arn:aws:logs:${local.region}:${local.account_id}:log-group:${module.logs_label.id}" : ""

logs_bucket_enabled = var.session_logging_enabled && length(var.session_logging_bucket_name) == 0
}
Expand All @@ -57,68 +64,6 @@ locals {
## SSM AGENT ROLE ##
###################

data "aws_iam_policy_document" "default" {

statement {
effect = "Allow"
actions = ["sts:AssumeRole"]

principals {
type = "Service"
identifiers = ["ec2.amazonaws.com"]
}
}
}

data "aws_s3_bucket" "logs_bucket" {
count = var.session_logging_enabled ? 1 : 0
bucket = try(coalesce(var.session_logging_bucket_name, module.logs_bucket.bucket_id), "")
}

# https://docs.aws.amazon.com/systems-manager/latest/userguide/getting-started-create-iam-instance-profile.html#create-iam-instance-profile-ssn-logging
data "aws_iam_policy_document" "session_logging" {
count = var.session_logging_enabled ? 1 : 0

statement {
sid = "SSMAgentSessionAllowS3Logging"
effect = "Allow"
actions = [
"s3:PutObject"
]
resources = ["${join("", data.aws_s3_bucket.logs_bucket.*.arn)}/*"]
}

statement {
sid = "SSMAgentSessionAllowCloudWatchLogging"
effect = "Allow"
actions = [
"logs:CreateLogStream",
"logs:PutLogEvents",
"logs:DescribeLogGroups",
"logs:DescribeLogStreams"
]
resources = ["*"]
}

statement {
sid = "SSMAgentSessionAllowGetEncryptionConfig"
effect = "Allow"
actions = [
"s3:GetEncryptionConfiguration"
]
resources = ["*"]
}

statement {
sid = "SSMAgentSessionAllowKMSDataKey"
effect = "Allow"
actions = [
"kms:GenerateDataKey"
]
resources = ["*"]
}
}

resource "aws_iam_role" "default" {
name = module.role_label.id
assume_role_policy = data.aws_iam_policy_document.default.json
Expand Down Expand Up @@ -157,19 +102,21 @@ resource "aws_iam_instance_profile" "default" {
###################

resource "aws_security_group" "default" {
vpc_id = var.vpc_id
vpc_id = local.vpc_id
name = module.this.id
description = "Allow ALL egress from SSM Agent."
tags = module.this.tags
}

# trivy:ignore:aws-vpc-no-public-egress-sgr SSM Agent requires broad egress to communicate with AWS services
resource "aws_security_group_rule" "allow_all_egress" {
type = "egress"
from_port = 0
to_port = 0
protocol = "-1"
cidr_blocks = ["0.0.0.0/0"]
ipv6_cidr_blocks = ["::/0"]
description = "Allow all outbound traffic for SSM Agent communication with AWS services"
security_group_id = aws_security_group.default.id
}

Expand Down Expand Up @@ -246,21 +193,15 @@ DOC

module "logs_bucket" {
source = "cloudposse/s3-bucket/aws"
version = "3.1.2"
version = "4.10.0"

enabled = local.logs_bucket_enabled
context = module.logs_label.context

# Encryption / Security
acl = "private"
sse_algorithm = "aws:kms"
kms_master_key_arn = local.session_logging_kms_key_arn
allow_encrypted_uploads_only = false
force_destroy = true

# Feature enablement
user_enabled = false
versioning_enabled = true
sse_algorithm = "aws:kms"
kms_master_key_arn = local.session_logging_kms_key_arn
force_destroy = true

lifecycle_configuration_rules = [{
enabled = true
Expand Down Expand Up @@ -385,7 +326,7 @@ resource "aws_autoscaling_group" "default" {
# By default, we don't care to protect from scale in as we want to roll instances frequently
protect_from_scale_in = var.protect_from_scale_in

vpc_zone_identifier = var.subnet_ids
vpc_zone_identifier = local.subnet_ids

default_cooldown = 180
health_check_grace_period = 180
Expand Down
4 changes: 2 additions & 2 deletions outputs.tf
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Expand Up @@ -24,11 +24,11 @@ output "role_id" {
}

output "session_logging_bucket_id" {
value = local.logs_bucket_enabled ? join("", data.aws_s3_bucket.logs_bucket.*.id) : ""
value = var.session_logging_enabled ? local.session_logging_bucket_name : ""
description = "The ID of the SSM Agent Session Logging S3 Bucket."
}

output "session_logging_bucket_arn" {
value = local.logs_bucket_enabled ? join("", data.aws_s3_bucket.logs_bucket.*.arn) : ""
value = local.session_logging_bucket_arn
description = "The ARN of the SSM Agent Session Logging S3 Bucket."
}
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