Terraform AWS ECS Cluster

A Terraform module for building an ECS Cluster in AWS.

The ECS cluster requires:

• An existing VPC
• Some existing subnets

The ECS cluster consists of:

• A cluster in ECS
• A launch template and auto-scaling group for a cluster of ECS container instances
• An SSH key to connect to the ECS container instances
• A security group for the container instances optionally allowing:
  • Outbound internet access for all containers
  • Inbound TCP access on any port from the VPC network
• An IAM role and policy for the container instances allowing:
  • ECS interactions
  • ECR image pulls
  • S3 object fetches
  • Logging to cloudwatch
• An IAM role and policy for ECS services allowing:
  • Elastic load balancer registration / deregistration
  • EC2 describe actions and security group ingress rule creation
• A CloudWatch log group

Usage

To use the module, include something like the following in your Terraform configuration:

module "ecs_cluster" {
  source  = "infrablocks/ecs-cluster/aws"
  version = "5.0.0"

  region     = "eu-west-2"
  vpc_id     = "vpc-fb7dc365"
  subnet_ids = [
    "subnet-eb32c271",
    "subnet-64872d1f"
  ]

  component             = "important-component"
  deployment_identifier = "production"

  cluster_name                         = "services"
  cluster_instance_ssh_public_key_path = "~/.ssh/id_rsa.pub"
  cluster_instance_type                = "t3.small"

  cluster_minimum_size     = 2
  cluster_maximum_size     = 10
  cluster_desired_capacity = 4
}

As mentioned above, the ECS cluster deploys into an existing base network. Whilst the base network can be created using any mechanism you like, the AWS Base Networking module will create everything you need. See the docs for usage instructions.

See the Terraform registry entry for more details.

Inputs

Name	Description	Default	Required
region	The region into which to deploy the cluster	-	yes
vpc_id	The ID of the VPC into which to deploy the cluster	-	yes
subnet_ids	The IDs of the subnets for container instances	-	yes
component	The component this cluster will contain	-	yes
deployment_identifier	An identifier for this instantiation	-	yes
tags	A map of additional tags to add to all resources	-	no
cluster_name	The name of the cluster to create	default	yes
cluster_instance_ssh_public_key_path	The path to the public key to use for the container instances	-	yes
cluster_instance_type	The instance type of the container instances	t2.medium	yes
cluster_instance_root_block_device_size	The size in GB of the root block device on cluster instances	30	yes
cluster_instance_root_block_device_path	Path of the instance root block storage volume	/dev/xvda	yes
cluster_instance_root_block_device_type	The type of the root block device on cluster instances ('standard', 'gp2', or 'io1')	standard	yes
cluster_instance_user_data_template	The contents of a template for container instance user data	see user-data	no
cluster_instance_ami	AMI for the container instances	ECS optimised AMI	yes
cluster_instance_metadata_options	A map of metadata options for cluster instances.	-	no
cluster_instance_iam_policy_contents	The contents of the cluster instance IAM policy	see policies	no
cluster_service_iam_policy_contents	The contents of the cluster service IAM policy	see policies	no
cluster_minimum_size	The minimum size of the ECS cluster	1	yes
cluster_maximum_size	The maximum size of the ECS cluster	10	yes
cluster_desired_capacity	The desired capacity of the ECS cluster	3	yes
associate_public_ip_addresses	Whether or not to associate public IP addresses with ECS container instances	false	no
include_default_ingress_rule	Whether or not to include the default ingress rule on the ECS container instances security group	true	no
include_default_egress_rule	Whether or not to include the default egress rule on the ECS container instances security group	true	no
default_ingress_cidrs	The CIDRs allowed access to containers	["10.0.0.0/8"]	if include_default_ingress_rule
default_egress_cidrs	The CIDRs accessible from containers	["0.0.0.0/0"]	if include_default_egress_rule
security_groups	The list of security group IDs to associate with the cluster in addition to the default security group	[]	no
cluster_log_group_retention	The number of days logs will be retained in the CloudWatch log group of the cluster (0 = unlimited)	0	no
enable_detailed_monitoring	Enable detailed monitoring of EC2 instance(s)	true	no
enable_container_insights	Whether or not to enable container insights on the ECS cluster	false	no
protect_cluster_instances_from_scale_in	Whether or not to protect cluster instances in the autoscaling group from scale in	false	no
include_asg_capacity_provider	Whether or not to add the created ASG as a capacity provider for the ECS cluster	false	no
asg_capacity_provider_manage_termination_protection	Whether or not to allow ECS to manage termination protection for the ASG capacity provider	true	no
asg_capacity_provider_manage_scaling	Whether or not to allow ECS to manage scaling for the ASG capacity provider	true	no
asg_capacity_provider_minimum_scaling_step_size	The minimum scaling step size for ECS managed scaling of the ASG capacity provider	1	no
asg_capacity_provider_maximum_scaling_step_size	The maximum scaling step size for ECS managed scaling of the ASG capacity provider	1000	no
asg_capacity_provider_target_capacity	The target capacity, as a percentage from 1 to 100, for the ASG capacity provider	100	no
cluster_instance_enable_ebs_volume_encryption	Determines whether encryption is enabled on the EBS volume	true	no
cluster_instance_ebs_volume_kms_key_id	KMS key to use for encryption of the EBS volume when enabled	alias/aws/ebs	no

Notes:

• By default, the latest available Amazon Linux 2 AMI is used.
• For Amazon Linux 1 AMIs use version <= 0.6.0 of this module for terraform 0.11 or version = 1.0.0 for terraform 0.12.
• When a specific AMI is provided via cluster_instance_ami, only the root block device can be customised, using the cluster_instance_root_block_device_size and cluster_instance_root_block_device_type variables.
• The user data template will get the cluster name as cluster_name. If none is supplied, a default will be used.

Outputs

Name	Description
cluster_id	The ID of the created ECS cluster
cluster_name	The name of the created ECS cluster
cluster_arn	The ARN of the created ECS cluster
autoscaling_group_name	The name of the autoscaling group for the ECS container instances
launch_template_name	The name of the launch template for the ECS container instances
launch_template_id	The ID of the launch template for the ECS container instances
security_group_id	The ID of the default security group associated with the ECS container instances
instance_role_arn	The ARN of the container instance role
instance_role_id	The ID of the container instance role
instance_policy_arn	The ARN of the container instance policy
instance_policy_id	The ID of the container instance policy
service_role_arn	The ARN of the ECS service role
service_role_id	The ID of the ECS service role
service_policy_arn	The ARN of the ECS service policy
service_policy_id	The ID of the ECS service policy
log_group	The name of the default log group for the cluster

Compatibility

This module is compatible with Terraform versions greater than or equal to Terraform 1.0.

Required Permissions

• iam:GetPolicy
• iam:GetPolicyVersion
• iam:ListPolicyVersions
• iam:ListEntitiesForPolicy
• iam:CreatePolicy
• iam:DeletePolicy
• iam:GetRole
• iam:PassRole
• iam:CreateRole
• iam:DeleteRole
• iam:ListRolePolicies
• iam:AttachRolePolicy
• iam:DetachRolePolicy
• iam:GetInstanceProfile
• iam:CreateInstanceProfile
• iam:ListInstanceProfilesForRole
• iam:AddRoleToInstanceProfile
• iam:RemoveRoleFromInstanceProfile
• iam:DeleteInstanceProfile
• ec2:DescribeSecurityGroups
• ec2:CreateSecurityGroup
• ec2:DeleteSecurityGroup
• ec2:AuthorizeSecurityGroupIngress
• ec2:AuthorizeSecurityGroupEgress
• ec2:RevokeSecurityGroupEgress
• ec2:ImportKeyPair
• ec2:DescribeKeyPairs
• ec2:DeleteKeyPair
• ec2:CreateTags
• ec2:DescribeImages
• ec2:DescribeNetworkInterfaces
• ecs:DescribeClusters
• ecs:CreateCluster
• ecs:DeleteCluster
• autoscaling:DescribeLaunchConfigurations
• autoscaling:CreateLaunchConfiguration
• autoscaling:DeleteLaunchConfiguration
• autoscaling:DescribeScalingActivities
• autoscaling:DescribeAutoScalingGroups
• autoscaling:CreateAutoScalingGroup
• autoscaling:UpdateAutoScalingGroup
• autoscaling:DeleteAutoScalingGroup
• logs:CreateLogGroup
• logs:DescribeLogGroups
• logs:ListTagsLogGroup
• logs:DeleteLogGroup

Development

Machine Requirements

In order for the build to run correctly, a few tools will need to be installed on your development machine:

• Ruby (3.1)
• Bundler
• git
• git-crypt
• gnupg
• direnv
• aws-vault

Mac OS X Setup

Installing the required tools is best managed by homebrew.

To install homebrew:

ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"

Then, to install the required tools:

# ruby
brew install rbenv
brew install ruby-build
echo 'eval "$(rbenv init - bash)"' >> ~/.bash_profile
echo 'eval "$(rbenv init - zsh)"' >> ~/.zshrc
eval "$(rbenv init -)"
rbenv install 3.1.1
rbenv rehash
rbenv local 3.1.1
gem install bundler

# git, git-crypt, gnupg
brew install git
brew install git-crypt
brew install gnupg

# aws-vault
brew cask install

# direnv
brew install direnv
echo "$(direnv hook bash)" >> ~/.bash_profile
echo "$(direnv hook zsh)" >> ~/.zshrc
eval "$(direnv hook $SHELL)"

direnv allow <repository-directory>

Running the build

Running the build requires an AWS account and AWS credentials. You are free to configure credentials however you like as long as an access key ID and secret access key are available. These instructions utilise aws-vault which makes credential management easy and secure.

To provision module infrastructure, run tests and then destroy that infrastructure, execute:

aws-vault exec <profile> -- ./go

To provision the module prerequisites:

aws-vault exec <profile> -- ./go deployment:prerequisites:provision[<deployment_identifier>]

To provision the module contents:

aws-vault exec <profile> -- ./go deployment:root:provision[<deployment_identifier>]

To destroy the module contents:

aws-vault exec <profile> -- ./go deployment:root:destroy[<deployment_identifier>]

To destroy the module prerequisites:

aws-vault exec <profile> -- ./go deployment:prerequisites:destroy[<deployment_identifier>]

Configuration parameters can be overridden via environment variables:

DEPLOYMENT_IDENTIFIER=testing aws-vault exec <profile> -- ./go

When a deployment identifier is provided via an environment variable, infrastructure will not be destroyed at the end of test execution. This can be useful during development to avoid lengthy provision and destroy cycles.

Common Tasks

Generating an SSH key pair

To generate an SSH key pair:

ssh-keygen -m PEM -t rsa -b 4096 -C [email protected] -N '' -f config/secrets/keys/bastion/ssh

Generating a self-signed certificate

To generate a self signed certificate:

openssl req -x509 -newkey rsa:4096 -keyout key.pem -out cert.pem -days 365

To decrypt the resulting key:

openssl rsa -in key.pem -out ssl.key

Managing CircleCI keys

To encrypt a GPG key for use by CircleCI:

openssl aes-256-cbc \
  -e \
  -md sha1 \
  -in ./config/secrets/ci/gpg.private \
  -out ./.circleci/gpg.private.enc \
  -k "<passphrase>"

To check decryption is working correctly:

openssl aes-256-cbc \
  -d \
  -md sha1 \
  -in ./.circleci/gpg.private.enc \
  -k "<passphrase>"

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/infrablocks/terraform-aws-assumable-roles-policy. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the Contributor Covenant code of conduct.

License

The library is available as open source under the terms of the MIT License.