The Path Towards Enterprise Level AWS Infrastructure – EC2, AMI, Bastion Host, RDS

Let’s pick up the thread of our journey into the AWS Cloud, and keep discovering the intrinsics of the cloud computing universe while building a highly available, secure and fault-tolerant cloud system on the AWS platform.

This article is the second one of the mini-series which walks you through the process of creating an enterprise-level AWS infrastructure and explains concepts and components of the Amazon Web Services platform. In the previous part, we scaffolded our infrastructure; specifically, we created the VPC, subnets, NAT gateways, and configured network routing. If you have missed that, we strongly encourage you to read it first → Part 1 - Architecture Scaffolding (VPC, Subnets, Elastic IP, NAT).

In this article, we will build on top of the work we have done in the previous part, and this time we focus on the configuration of EC2 instances, the creation of AMI images, setting up Bastion Hosts, and RDS database.

The whole series comprises of:

Part 1 - Architecture Scaffolding (VPC, Subnets, Elastic IP, NAT).
Part 2 - The Path Towards Enterprise Level AWS Infrastructure – EC2, AMI, Bastion Host, RDS.
Part 3 - Load Balancing and Application Deployment (Elastic Load Balancer)

Infrastructure Overview

The diagram below presents our designed infrastructure. If you would like to learn more about design choices behind it, please read Part 1 - Architecture Scaffolding (VPC, Subnets, Elastic IP, NAT). We have already created a VPC, subnets, NAT Gateways, and configured network routing. In this part of the series, we focus on the configuration of required EC2 instances, the creation of AMI images, setting up Bastion Hosts, and the RDS database.

Figure 1Figure 1

AWS Theory

1. Elastic Cloud Compute Cloud (EC2)

Elastic Cloud Compute Cloud (EC2) is an Amazon service that allows you to manage your virtual computing environments, known as EC2 instances, on AWS. An EC2 instance is simply a virtual machine provisioned with a certain amount of resources such as CPU, memory, storage, and network capacity launched in a selected AWS region and availability zone. The elasticity of EC2 means that you can scale up or down resources easily, depending on your needs and requirements. The network security of your instances can be managed with the use of security groups by the configuration of protocols, ports, and IP addresses that your instances can communicate with.

There are five basic types of EC2 instances, which you can use based on your system requirements.

  • General Purpose,
  • Compute Optimized,
  • Memory Optimized,
  • Accelerated Computing,
  • Storage Optimized.

In our infrastructure, we will use only general-purpose instances, but if you would like to learn more about different features of instance types, see the AWS documentation.

All EC2 instances come with instance store volumes for temporary data that is deleted whenever the instance is stopped or terminated, as well as with Elastic Block Store (EBS), which is a persistent storage volume working independently of the EC2 instance itself.

Figure 2Figure 2

2. Amazon Machine Images (AMI)

Amazon utilizes templates of software configurations, known as Amazon Machine Images (AMI), in order to facilitate the creation of custom EC2 instances. AMIs are image templates that contain software such as operating systems, runtime environments, and actual applications that are used to launch EC2 instances. This allows us to preconfigure our AMIs and dynamically launch new instances on the go using this image instead of always setting up VM environments from scratch. Amazon provides some ready to use AMIs on the AWS Marketplace, which you can extend, customize, and save as your own (which we will do soon).

3. Key Pair

Amazon provides a secure EC2 login mechanism with the use of public-key cryptography. During the instance boot time, the public key is put in an entry within ~/.ssh/authorized_keys, and then you can securely access your instance through SSH using a private key instead of a password. The public and private keys are known as a key pair.

4. IAM Role

IAM means Identity and Access Management and it defines authentication and authorization rules for your system. IAM roles are IAM identities which comprise a set of permissions that control access to AWS services and can be attached to AWS resources such as users, applications, or services. As an example, if your application needs access to a specific AWS service such as an S3 Bucket, its EC2 instance needs to have a role with appropriate permission assigned.

5. Bastion Host

Bastion Host is a special purpose instance placed in a public subnet, which is used to allow access to instances located in private subnets while providing an increased level of security. It acts as a bridge between users and private instances, and due to its exposure to potential attacks, it is configured to withstand any penetration attempts. The private instances only expose their SSH ports to a bastion host, not allowing any direct connection. What is more, bastion hosts may be configured to log any activity providing additional security auditing.

Figure 3Figure 3

6. Amazon Relational Database Service (RDS)

6.1. RDS

RDS is an Amazon service for the management of relational databases in the cloud. As of now (23.04.2020), it supports six database engines specifically Amazon Aurora, PostgreSQL, MySQL, MariaDB, Oracle Database, and SQL Server. It is easy to configure, scale and it provides high availability and reliability with the use of Read Replicas and Multi-AZ Deployment features.

6.2. Read Replicas

RDS Read Replicas are asynchronous, read-only instances that are replicas of a primary “master” db instance. They can be used for handling queries that do not require any data change, thus reliving the workload from the master node.

6.3. Multi-AZ Deployment

AWS Multi-AZ Deployment is an option to allow RDS to create a secondary, standby instance in a different AZ, and replicate it synchronously with the data from the master node. Both master and standby instances run on their own physically independent infrastructures, and only the primary instance can be accessed directly. The standby replica is used as a failover in case of any master’s failure, without changing the endpoint of your DB.

This reduces downtime of your system and makes it easier to perform version upgrades or create backup snapshots, as they can be done on the spare instance. Multi-AZ is usually used only on the master instance. However, it is also possible to create read replicas with Multi-AZ deployment, which results in a resilient disaster recovery infrastructure.

Practice

We have two applications that we would like to run on our AWS infrastructure. One is a Java 11 Spring Boot application, so the EC2 which will host it is required to have Java 11 installed. The second one is a React.js frontend application, which requires a virtual machine with a Node.js environment. Therefore, as the first step, we are going to set up a Bastion Host, which will allow us to ssh our instances. Then, we will launch and configure those two EC2 instances manually in the first availability zone. Later on, we will create AMIs based on those instances and use them for the creation of EC2s in the second availability zone.

1. Availability Zone A

1.1. Bastion Host

A Bastion Host is nothing more than a special-purpose EC2 instance. Hence, in order to create a Bastion Host, go into the AWS Management Console, and search for EC2 service. Then click the Launch Instance button, and you will be shown with an EC2 launch wizard. The first step is the selection of an AMI image for your instance. You can filter AMIs and select one based on your preferences. In this article, we will use the Amazon Linux 2 AMI (HVM), SSD Volume Type image.

Figure 4Figure 4

On the next screen, we need to choose an instance type for our image. Here, I am sticking with the AWS free tier program, so I will go with the general-purpose t2.micro type. Click Next: Configure instance Details. Here, we can define the number of instances, network settings, IAM configuration, etc. For now, let’s start with 1 instance, we will work on the scalability of our infrastructure later. In the Network section, choose your previously created VPC and public-subnet-a and enable Public IP auto-assignment. We do not need to specify any IAM role as we are not going to use any of the AWS services.

Figure 5Figure 5

Click Next. Here you can see that the wizard automatically configures your instance with an 8GB EBS storage, which is enough for us. Click Next again. Now, we can add tags to improve the recognizability of our instance. Let’s add a Name tag bastion-a-ec2. On the next screen, we can configure a security group for our instance. Create a new security group, name it bastion-sg.

You can see that there is already one predefined rule exposing our instance for SSH sessions from 0.0.0.0/0 (anywhere). You should change it here to allow only connections from your IP address. The important thing to note here is that in the production environment you would never expose your instances to the whole world, instead, you would whitelist the IP addresses of employees allowed to connect to your instance.

Figure 6Figure 6

In the next step, you can review your EC2 configuration and launch it. The last action is the creation of a key pair. This is important because we need this key pair to ssh to our instance. Name the key pair e.g. user-manager-key-pair, download the private key, and store it locally on your machine. This is it, Amazon will take some time, but in the end, your EC2 instance will be launched.

Figure 7Figure 7

In the instance description section, you can find the public IP address of your instance. We can use it to ssh to the EC2. That is where we will need previously generated and hopefully locally saved private key (*.pem file). That’s it, our instance is ready for now. However, in production, it would be a good idea to harden the security of the Bastion Host even more. If you would like to learn more about that, we recommend this article.

1.2. Backend Server EC2

Now, let’s create an instance for the backend server. Click Launch instance again, choose the same AMI image as before, place it in your user-manager-vpc, private-subnet-a, and do not enable public IP auto-assignment this time. Move through the next steps as before, add a server-a-ec2 name tag. In the security group configuration, create a new security group, and modify its settings to allow SSH incoming communication only from the bastion-sg.

Figure 8Figure 8

Launch the instance. You can create a new key pair or use the previously created one (for simplicity I recommend using the same key pair for all instances). In the end, you should have your second instance up and running.

Figure 9Figure 9

You can see that server-a-ec2 does not have any public IP address. However, we can access it through the bastion host. First, we need to add our key to a keychain and then we can ssh to our bastion host instance adding -A flag to the ssh command. This flag enables agent-forwarding, which will let you ssh into your private instance without explicitly specifying private key again. This is a recommended way, which lets you avoid storage of the private key on the bastion host instance which could lead to a security breach.


ssh-add -k 
ssh -A -i path-to-your-pem-file ec2-user@bastion-a-ec2-instance-public-ip

Then, inside your bastion host execute the command:


ssh ec2-user@server-a-ec2-instance-private-ip

Now, you should be inside your server-a-ec2 private instance. Let’s install the required software on the machine by executing those commands:


sudo yum update -y &&
sudo amazon-linux-extras enable corretto8 &&
sudo yum clean metadata &&
sudo yum install java-11-amazon-corretto &&
java --version

As a result, you should have java 11 installed on your server-a-ec2 instance. You can go back to the local command prompt by executing the exit command twice.

AMI

The ec2 instance for the backend server is ready for the deployment. In the second availability zone, we could follow exactly the same steps. However, there is an easier way. We can create an AMI image based on our pre-configured instance and use it later for the creation of the corresponding instance in availability zone b. In order to do that, go again into the Instances menu, select your instance, click Actions -> Image -> Create image. Your AMI image will be created and you will be able to find it in the Images/AMIs section.

Figure 10Figure 10

1.3. Client Application EC2

The last EC2 instance we need in the Availability Zone A will host the client application. So, let’s go once again through the process of EC2 creation. Launch instance, select the same base AMI as before, select your VPC, place the instance in the public-subnet-a, and enable public IP assignment. Then, add a client-a-ec2 Name tag, and create a new security group client-sg allowing SSH incoming connection from the bastion-sg security group. That’s it, launch it.

Figure 11Figure 11

Now, SSH to the instance through the bastion host, and install the required software.


ssh -A -i path-to-your-pem-file ec2-user@bastion-a-ec2-instance-public-ip

Then, inside your bastion host execute the command:


ssh -A -i path-to-your-pem-file ec2-user@bastion-a-ec2-instance-public-ip

Inside client-a-ec2 command prompt, execute :


sudo yum update &&
curl -sL https://rpm.nodesource.com/setup_12.x | sudo bash - &&
sudo yum install -y nodejs &&
node -v &&
npm -v

Exit the EC2 command prompt and create a new AMI image based on it.

Figure 12Figure 12

2. Availability Zone B

2.1. Bastion Host

Create the second bastion host instance following the same steps as for availability zone a, but this time place it in public-subnet-b, add Name tag bastion-b-ec2, and assign to it previously created bastion-sg security group.

2.2. Backend Server EC2

For the backend server EC2, go again to the Launch Instance menu, and this time instead of using Amazon’s AMI switch to My AMI’s tab and select the previously created server-ami image. Place the instance in the private-subnet-b, add a name tag server-b-ec2, and assign to it the server-sg security group.

Figure 13Figure 13

2.3. Client Application EC2

Just as for the backend server instance, launch the client-b-ec2 using your custom AMI image. This time select the client-ami image, place EC2 in the public-subnet-b, enable automatic IP assignment, and choose the client-sg security group.

3. RDS

We have all our EC2 instances ready. The last part which we will cover in this article is the configuration of RDS. For that, go into the RDS service in the AWS Management Console and click Create database. In the database configuration window, follow the standard configuration path. Select MySQL db engine, and select Free tier template. Set your db name as user-manager-db, specify master username and password, select your user-manager-vpc, availability zone a, and make the database publicly not accessible. Create also a new user-manager-db-sg security group.

Figure 14Figure 14

In the Additional configuration section, specify the initial db name, and finally create a database.

Figure 15Figure 15

After AWS finishes the creation process, you will be able to get the database endpoint, which we will use to connect to the database from our application later on. Now, in order to provide high availability of the database, click the Modify button on the created database screen, and enable Multi-AZ deployment. Please, bear in mind that Multi-AZ deployment is not included in the free tier program, so if you would like to avoid any charges, skip this point.

Figure 16Figure 16

As the last step, we need to add a rule to the user-manager-db-sg to allow incoming connections from our server-sg on port 3306 in order to allow communication between our server and the database.

Figure 17Figure 17

Summary

Congratulations, our infrastructure is almost ready for deployment. As you can see in our final diagram, the only thing which is missing is the load balancer. In the next part of the series, we will take care of that, and deploy our applications to have a fully functioning system running on AWS infrastructure!

Figure 18Figure 18

Sources:

https://cloudacademy.com/blog/aws-bastion-host-nat-instances-vpc-peering-security/
https://aws.amazon.com/quickstart/architecture/linux-bastion/
https://aws.amazon.com/blogs/security/securely-connect-to-linux-instances-running-in-a-private-amazon-vpc/
https://app.pluralsight.com/library/courses/aws-developer-getting-started/table-of-contents
https://app.pluralsight.com/library/courses/aws-developer-designing-developing/table-of-contents
https://app.pluralsight.com/library/courses/aws-networking-deep-dive-vpc/table-of-contents
https://www.techradar.com/news/what-is-amazon-rds
https://medium.com/kaodim-engineering/hardening-ssh-using-aws-bastion-and-mfa-45d491288872
https://cloudacademy.com/blog/aws-bastion-host-nat-instances-vpc-peering-security/
https://docs.aws.amazon.com/IAM/latest/UserGuide/id_roles.html
https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/ec2-key-pairs.html
https://aws.amazon.com/ec2/instance-types/
https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/concepts.html

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