Terraform AWS Application Load Balancer

A Terraform module for building an application load balancer in AWS.

The load balancer requires:

• An existing VPC
• Some existing subnets
• A domain name and public and private hosted zones

The application load balancer consists of:

• An ALB
  • Deployed across the provided subnet IDs
  • Either internal or internet-facing as specified
  • With a health check using the specified target
  • With connection draining as specified
• A security group allowing access to/from the load balancer according to the specified access control and egress CIDRs configuration
• A security group for use by instances allowing access from the load balancer according to the specified access control configuration
• A DNS entry
  • In the public hosted zone if specified
  • In the private hosted zone if specified

Usage

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

module "application_load_balancer" {
  source  = "infrablocks/application-load-balancer/aws"
  version = "0.1.0"

  region = "eu-west-2"
  vpc_id = "vpc-fb7dc365"
  subnet_ids = "subnet-ae4533c4,subnet-443e6b12"
  
  component = "important-component"
  deployment_identifier = "production"
  
  domain_name = "example.com"
  public_zone_id = "Z1WA3EVJBXSQ2V"
  private_zone_id = "Z3CVA9QD5NHSW3"
  
  listeners = [
    {
      lb_port = 443
      lb_protocol = "HTTPS"
      instance_port = 443
      instance_protocol = "HTTPS"
      ssl_certificate_id = "arn:aws:iam::123456789012:server-certificate/default"
    },
    {
      lb_port = 6567
      lb_protocol = "TCP"
      instance_port = 6567
      instance_protocol = "TCP"
    }
  ]
  
  access_control = [
    {
      lb_port = 443
      instance_port = 443
      allow_cidr = '0.0.0.0/0'
    },
    {
      lb_port = 6567
      instance_port = 6567
      allow_cidr = '10.0.0.0/8'
    }
  ]
  
  egress_cidrs = '10.0.0.0/8'
  
  health_check_target = 'HTTPS:443/ping'
  health_check_timeout = 10
  health_check_interval = 30
  health_check_unhealthy_threshold = 5
  health_check_healthy_threshold = 5

  enable_cross_zone_load_balancing = 'yes'

  enable_connection_draining = 'yes'
  connection_draining_timeout = 60

  idle_timeout = 60

  include_public_dns_record = 'yes'
  include_private_dns_record = 'yes'

  expose_to_public_internet = 'yes'
}

As mentioned above, the load balancer 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 load balancer	-	yes
vpc_id	The ID of the VPC into which to deploy the load balancer	-	yes
subnet_ids	The IDs of the subnets for the ALB	-	yes
component	The component for which the load balancer is being created	-	yes
deployment_identifier	An identifier for this instantiation	-	yes
domain_name	The domain name of the supplied Route 53 zones	-	yes
public_zone_id	The ID of the public Route 53 zone	-	yes
private_zone_id	The ID of the private Route 53 zone	-	yes
enable_cross_zone_load_balancing	Whether or not to enable cross zone load balancing ("yes" or "no").	no	no
idle_timeout	The time after which idle connections are closed.	60	no
include_public_dns_record	Whether or not to create a public DNS entry ("yes" or "no").	no	no
include_private_dns_record	Whether or not to create a private DNS entry ("yes" or "no").	yes	no
expose_to_public_internet	Whether or not to the ALB should be internet facing ("yes" or "no").	no	no
use_https	whether or not to use HTTPS	no	no
target_group_port	The port that the application is listening on	-	yes
target_group_type	The type of target that you must specify when registering targets with this target group.	instance	no
target_group_protocol	The protocol to use for routing traffic to the targets. Should be either HTTP or HTTPS	HTTP	no
health_check_port	The port to use to connect with the target. Either ports 1-65536, or traffic-port	traffic-port	no
health_check_protocol	The protocol to use for health checks	HTTP	no
health_check_interval	The time between health check attempts in seconds	30	no
health_check_unhealthy_threshold	The number of failed health checks before an instance is taken out of service	2	no
health_check_healthy_threshold	The number of successful health checks before an instance is put into service	10	no
listener_port	Port that ALB listens on	443	no
listener_protocol	Protocol that the ALB listens on	HTTPS	no
listener_certificate_arn	certificate ARN to be used by the certificate	-	yes

Outputs

Name	Description
name	The name of the created ALB
arn	The arn of the created ALB
zone_id	The zone ID of the created ALB
dns_name	The DNS name of the created ALB
address	The address of the DNS record(s) for the created ALB

Compatibility

This module is compatible with Terraform versions greater than or equal to Terraform 0.14.

Development

Machine Requirements

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

• Ruby (2.3.1)
• Bundler
• git
• git-crypt
• gnupg
• direnv

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 2.3.1
rbenv rehash
rbenv local 2.3.1
gem install bundler

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

# 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

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

./go

To provision the module prerequisites:

./go deployment:prerequisites:provision[<deployment_identifier>]

To provision the module contents:

./go deployment:harness:provision[<deployment_identifier>]

To destroy the module contents:

./go deployment:harness:destroy[<deployment_identifier>]

To destroy the module prerequisites:

./go deployment:prerequisites:destroy[<deployment_identifier>]

Common Tasks

Generating an SSH key pair

To generate an SSH key pair:

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

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-application-load-balancer. 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.