AWScloud~10 mins

High availability design patterns in AWS - Commands & Configuration

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Introduction

High availability design patterns help keep your applications running without interruption. They reduce downtime by using multiple resources that can take over if one fails.

When you want your website to stay online even if one server crashes

When you need your database to be accessible all the time without losing data

When you want to handle sudden traffic spikes without slowing down

When you want to deploy your app across different locations to avoid regional failures

When you want automatic recovery from hardware or software failures

Config File - main.tf

main.tf

provider "aws" {
  region = "us-east-1"
}

resource "aws_vpc" "main" {
  cidr_block = "10.0.0.0/16"
}

resource "aws_subnet" "subnet1" {
  vpc_id            = aws_vpc.main.id
  cidr_block        = "10.0.1.0/24"
  availability_zone = "us-east-1a"
}

resource "aws_subnet" "subnet2" {
  vpc_id            = aws_vpc.main.id
  cidr_block        = "10.0.2.0/24"
  availability_zone = "us-east-1b"
}

resource "aws_lb" "app_lb" {
  name               = "app-load-balancer"
  internal           = false
  load_balancer_type = "application"
  subnets            = [aws_subnet.subnet1.id, aws_subnet.subnet2.id]
}

resource "aws_autoscaling_group" "app_asg" {
  name                      = "app-asg"
  max_size                  = 4
  min_size                  = 2
  desired_capacity          = 2
  vpc_zone_identifier       = [aws_subnet.subnet1.id, aws_subnet.subnet2.id]
  health_check_type         = "ELB"
  health_check_grace_period = 300

  launch_configuration = aws_launch_configuration.app_lc.name
  target_group_arns    = [aws_lb_target_group.app_tg.arn]
}

resource "aws_launch_configuration" "app_lc" {
  name_prefix   = "app-lc-"
  image_id      = "ami-0c94855ba95c71c99"
  instance_type = "t3.micro"
  security_groups = [aws_security_group.app_sg.id]
  lifecycle {
    create_before_destroy = true
  }
}

resource "aws_lb_target_group" "app_tg" {
  name     = "app-target-group"
  port     = 80
  protocol = "HTTP"
  vpc_id   = aws_vpc.main.id
  health_check {
    path                = "/"
    interval            = 30
    timeout             = 5
    healthy_threshold   = 5
    unhealthy_threshold = 2
  }
}

resource "aws_lb_listener" "app_listener" {
  load_balancer_arn = aws_lb.app_lb.arn
  port              = 80
  protocol          = "HTTP"

  default_action {
    type             = "forward"
    target_group_arn = aws_lb_target_group.app_tg.arn
  }
}

resource "aws_security_group" "app_sg" {
  name        = "app-sg"
  description = "Allow HTTP inbound"
  vpc_id      = aws_vpc.main.id

  ingress {
    from_port   = 80
    to_port     = 80
    protocol    = "tcp"
    cidr_blocks = ["0.0.0.0/0"]
  }

  egress {
    from_port   = 0
    to_port     = 0
    protocol    = "-1"
    cidr_blocks = ["0.0.0.0/0"]
  }
}

This Terraform file creates a high availability setup on AWS.

VPC and Subnets: Defines a private network with two subnets in different availability zones for fault tolerance.
Load Balancer: Distributes incoming traffic across multiple instances.
Auto Scaling Group: Automatically manages the number of instances to handle load and replace failed ones.
Launch Configuration: Defines the instance type and settings for new instances.
Target Group and Listener: Connects the load balancer to the instances and listens on port 80.
Security Group: Allows HTTP traffic to the instances.

Commands

Initializes Terraform in the current directory to download necessary plugins and prepare for deployment.

Terminal

terraform init

Expected OutputExpected

Initializing the backend... Initializing provider plugins... - Finding latest version of hashicorp/aws... - Installing hashicorp/aws v4.0.0... - Installed hashicorp/aws v4.0.0 (signed by HashiCorp) Terraform has been successfully initialized! You may now begin working with Terraform. Try running "terraform plan" to see any changes required for your infrastructure.

Applies the Terraform configuration to create the high availability infrastructure automatically without asking for confirmation.

Terminal

terraform apply -auto-approve

Expected OutputExpected

aws_vpc.main: Creating... aws_vpc.main: Creation complete after 3s [id=vpc-0a1b2c3d4e5f6g7h8] aws_subnet.subnet1: Creating... aws_subnet.subnet2: Creating... aws_subnet.subnet1: Creation complete after 2s [id=subnet-0123456789abcdef0] aws_subnet.subnet2: Creation complete after 2s [id=subnet-0fedcba9876543210] aws_security_group.app_sg: Creating... aws_security_group.app_sg: Creation complete after 1s [id=sg-0a1b2c3d4e5f6g7h8] aws_launch_configuration.app_lc: Creating... aws_launch_configuration.app_lc: Creation complete after 1s [id=app-lc-20240610] aws_lb.app_lb: Creating... aws_lb.app_lb: Creation complete after 4s [id=app-load-balancer] aws_lb_target_group.app_tg: Creating... aws_lb_target_group.app_tg: Creation complete after 2s [id=app-target-group] aws_lb_listener.app_listener: Creating... aws_lb_listener.app_listener: Creation complete after 1s [id=app-listener] aws_autoscaling_group.app_asg: Creating... aws_autoscaling_group.app_asg: Creation complete after 3s [id=app-asg] Apply complete! Resources: 10 added, 0 changed, 0 destroyed.

→

-auto-approve - Skips manual approval to apply changes immediately

Checks the status and details of the created load balancer to confirm it is active and ready to route traffic.

Terminal

aws elbv2 describe-load-balancers --names app-load-balancer

Expected OutputExpected

{ "LoadBalancers": [ { "LoadBalancerArn": "arn:aws:elasticloadbalancing:us-east-1:123456789012:loadbalancer/app/app-load-balancer/50dc6c495c0c9188", "DNSName": "app-load-balancer-1234567890.us-east-1.elb.amazonaws.com", "CanonicalHostedZoneId": "Z35SXDOTRQ7X7K", "CreatedTime": "2024-06-10T12:00:00.000Z", "LoadBalancerName": "app-load-balancer", "Scheme": "internet-facing", "VpcId": "vpc-0a1b2c3d4e5f6g7h8", "State": { "Code": "active" }, "Type": "application", "AvailabilityZones": [ { "ZoneName": "us-east-1a", "SubnetId": "subnet-0123456789abcdef0" }, { "ZoneName": "us-east-1b", "SubnetId": "subnet-0fedcba9876543210" } ], "SecurityGroups": [ "sg-0a1b2c3d4e5f6g7h8" ] } ] }

→

--names - Specifies the load balancer name to describe

Verifies the auto scaling group is running the desired number of instances across availability zones for high availability.

Terminal

aws autoscaling describe-auto-scaling-groups --auto-scaling-group-names app-asg

Expected OutputExpected

{ "AutoScalingGroups": [ { "AutoScalingGroupName": "app-asg", "MinSize": 2, "MaxSize": 4, "DesiredCapacity": 2, "Instances": [ { "InstanceId": "i-0123456789abcdef0", "AvailabilityZone": "us-east-1a", "LifecycleState": "InService", "HealthStatus": "Healthy" }, { "InstanceId": "i-0fedcba9876543210", "AvailabilityZone": "us-east-1b", "LifecycleState": "InService", "HealthStatus": "Healthy" } ] } ] }

→

--auto-scaling-group-names - Specifies the auto scaling group to describe

Key Concept

If you remember nothing else from this pattern, remember: spreading resources across multiple zones with automatic failover keeps your app running even when parts fail.

Common Mistakes

Creating all resources in a single availability zone

If that zone fails, your whole app goes down, losing high availability.

Always deploy resources like subnets and instances in at least two different availability zones.

Not attaching instances to a load balancer

Traffic won't be distributed, and failed instances won't be replaced automatically.

Use a load balancer with target groups and auto scaling groups to manage traffic and health.

Setting min_size and desired_capacity to zero in auto scaling group

No instances will run, so your app will be offline.

Set min_size and desired_capacity to at least 1 to keep instances running.

Summary

Initialize Terraform to prepare the environment with 'terraform init'.

Apply the configuration to create high availability resources with 'terraform apply -auto-approve'.

Check the load balancer status to ensure it is active and ready.

Verify the auto scaling group is running instances in multiple availability zones.

Practice

(1/5)

1. What is the main goal of a high availability design pattern in AWS?

easy

A. To reduce the cost of cloud resources

B. To keep the application running even if some parts fail

C. To increase the speed of the application only

D. To limit the number of users accessing the app

Recommended

Ready to prove it?

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10 questions~5 mineasy hard

High availability design patterns in AWS - Commands & Configuration

Practice

Solution

Step 1: Understand high availability concept

Step 2: Match goal with options

Final Answer:

Quick Check:

Solution

Step 1: Identify service for traffic distribution

Step 2: Eliminate other options

Final Answer:

Quick Check:

Solution

Step 1: Understand multi-AZ deployment

Step 2: Analyze ELB behavior

Final Answer:

Quick Check:

Solution

Step 1: Check Auto Scaling group settings

Step 2: Understand failure impact

Final Answer:

Quick Check:

Solution

Step 1: Understand region failure scope

Step 2: Choose multi-region design

Final Answer:

Quick Check:

Ready to prove it?