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Three Tier Architecture with AWS

In this story, I am planning to create three-tier architecture with the help of AWS resources. First-tier Load Balancer, Second tier(webserver) considered as application logic and last tier Database. I am using Dynamodb for the NoSQL database.

Architecture

An auto-scaling group is created with a minimum of 2 instances. ASG has two subnets both in a different availability zone. This auto-scaling group will be used as a target group for application Load Balancer. In my configuration, instances are not reached directly via there public address over port 80 will only application load balancer will be forwarding a request to EC2 instance. Session get terminated at the application load balancer.

Two buckets are needed, the first S3 bucket used to store userdata and AWS Dynamodb script in S3. The second bucket will be used for ALB to store logs. IAM roles.

Configuration list

  • data.aws_ssm_parameter.s3bucket: S3 bucket information to storage scripts
  • aws_vpc.app_vpc: VPC for environment
  • aws_eip.lb_eip: Elastic IP address for Load balancer
  • aws_iam_role.app_s3_dynamodb_access_role: Role for EC2 instnace profile
  • data.aws_availability_zones.azs: To get list of all availability zones
  • data.aws_ssm_parameter.accesslogbucket: S3 bucketname to storage ALB logs
  • aws_dynamodb_table.app-dynamodb-table: Dynamoddb Table resource
  • aws_iam_role_policy.app_s3_dynamodb_access_role_policy: Policy to attach on role “app_s3_dynamodb_access_role”. Dynamodb full access is granted please grant appropriate access for your application need
  • aws_iam_instance_profile.app_instance_profile: EC2 instance profile to access S3 storage and Dynamodb table
  • aws_subnet.app_subnets: Multiple subnets are created with VPC per Availability zone in region
  • aws_lb_target_group.app-lb-tg: Target group for ALB
  • aws_security_group.app_sg_allow_public: Security group for LB. Port 80 open from all world.
  • aws_internet_gateway.app_ig: Internet gateway
  • aws_lb.app-lb: Application load balancer
  • app_s3_dynamodb_access_role : To access Dynamodb and S3 account from Lambda function
  • aws_route_table.app_rt: Route table
  • aws_security_group.app_sg_allow_localip: Security group to allow ssh access from “localip” from variables file and ALB to access EC2 instance over port 80
  • aws_instance.app-web: This is template instance will be used for AMI creation used for Launch configuration and Autoscaling group (ASG)
  • aws_lb_listener.app-lb_listner: ALB Listner for healthcheck
  • aws_ami_from_instance.app-ami: AMI resource will create ami from “app-web” instance. Will use this ami to create launch configuration.
  • aws_launch_configuration.app-launch-config: EC2 instnace launch configuration used to create Autoscalling group.
  • aws_autoscaling_group.app-asg: Autoscaling group used create two instance in different availability zone. ALB will send request on these ASG.

Source code

Please download source code from my GitHub Repo —

https://github.com/yogeshagrawal11/cloud/tree/master/aws/3%20Tier%20app

  • aws-userdata-script.sh : This will will run during userdata is executed. File will get information list instance-id, Publicip, lcoal ip and Availability zone name from metadata server and copy that to “/var/www/html/index.html” file.
  • nps_parks.csv : Is input file to copy data from S3 and add into dynamodb table
  • dynamodb.py : file used above input file and create new table and insert a record into the table. This table now used to sorting and output is store again in “/var/www/html/index.html” for future view. Objecting is to ensure instances from different availability zones able to comminited to Database our 3rd layer.
  • user_data.tpl : Userdata template file used by terraform
  • terraform.tfvars : Terraform varible file
  • main.tf : Terraform program file

PS. I don’t want to use this story to create a full-blown application.

Prerequisites

Download all files from the Github repository.

Download “terraform” software and copy at same downloaded location

Create S3 bucket to store scripts. Create “userdata” directory in bucket toplevel and upload “aws-userdata-script.sh”, “nps_parks.csv” and “dynamodb.py” file at that location. script “EC2 instance will copy these script using user-data template file.

Create key pair for EC2 instance.

Create the following parameter —

accesslogbucket : <buckname for ALB logs> You can use same bucket name as userdata.

ec2_keyname : <Key pair name>

s3bucket : s3://<bucketname>. Please ensure to prefix “s3://” before bucket name in value parameter.

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image -2

Configuration Output

Starting running terraform template you will see below output

The output is the Load balancer output link. You can add this output to DNS records for future access. For this exercise, we will use this address directly to access our application.

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image -3

Load balancer configuration. DNS name to access your ALB endpoint. VPc, Availability zone, and security group configuration. The public security group will be used to get traffic from world to ALB on port 80. image-5 has information about S3 location where ALB will going to save logs.

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image — 4
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image — 5

ALB target group configuration and health check details. Healthcheck is performed on “/” parent page. This can be changed as per different application endpoints. Image-7 has information about instances registered to the target group via the Autoscaling group.

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image — 6
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image — 7

I am first creating a sample instance “ya-web”. Using this application to create “golden-ami”. This AMI is been used for launch configuration and to create the Autoscaling Group(ASG). Normally golden AMI already created. That AMI information can be inputted as a variable in “terraform.tfvars” files. image — 9 is the Autoscaling group configuration. Minimum/maximum capacity can be altered as part of input as well.

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image — 8
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image — 9

Instance information. “ya-web” is a template vm. Other two vis are part of autoscaling group.

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image — 10

Accessing application with a Load Balancer. LB transferred the request to the first instance in AZ “us-west-2a”. Instance able to pull data from DynamoDB using boto API and because of instance profile, we created in our resource file. The image-12 request is transferred to a 2nd instance for different AZ “us-west-2b”. I am using stickiness for 20sec. This can be managed via cookies as well. My idea of the application is make it a simple kind of “hello world” application to get the bare minimum configuration.

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ALB transferring request to First instance, image-11
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ALB transferring request to First instance, image-12

Instance public IPs are not able to access from outside world(image — 13). Only ssh and ping(icmp) are allowed from localip defined variables file.

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image-13(a)
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image — 13(b)

Disclaimer

Network security and Identity security needed to be improved for production use.