Use this CDK stack to create a bastion host instance.

What is it?

Bastion hosts enables you to securely connect to your Linux instances without exposing your environment to the Internet. After you set up your bastion hosts, you can access the other instances in your VPC through Secure Shell (SSH) connections on Linux.

Features

• Deploy a bastion host instance in public subnet.

Prerequisites

You will need the following before utilize this CDK stack:

• AWS CLI
• AWS Account and User
• Node.js
• IDE for your programming language
• AWS CDK Tookit
• AWS Toolkit VSCode Extension

Stack Explain

cdk.json

Define project-name, env and profile context variables in cdk.json

{
  "context": {
    "project-name": "container",
    "env": "dev",
    "profile": "devopsrepo"
  }
}

lib/vpc-stack.ts

Setup standard VPC with public, private, and isolated subnets.

const vpc = new ec2.Vpc(this, 'Vpc', {
  maxAzs: 3,
  natGateways: 1,
  cidr: '10.0.0.0/16',
  subnetConfiguration: [
    {
      cidrMask: 24,
      name: 'ingress',
      subnetType: ec2.SubnetType.PUBLIC,
    },
    {
      cidrMask: 24,
      name: 'application',
      subnetType: ec2.SubnetType.PRIVATE,
    },
    {
      cidrMask: 28,
      name: 'rds',
      subnetType: ec2.SubnetType.ISOLATED,
    }
  ]
});

• maxAzs - Define 3 AZs to use in this region.
• natGateways - Create only 1 NAT Gateways/Instances.
• cidr - Use '10.0.0.0/16' CIDR range for the VPC.
• subnetConfiguration - Build the public, private, and isolated subnet for each AZ.

Create flowlog and log the vpc traffic into cloudwatch

vpc.addFlowLog('FlowLog');

lib/security-stack.ts

Get vpc create from vpc stack

const { vpc } = props;

Create security group for bastion host

const bastionSecurityGroup = new ec2.SecurityGroup(this, 'BastionSecurityGroup', {
  vpc: vpc,
  allowAllOutbound: true,
  description: 'Security group for bastion host',
  securityGroupName: 'BastionSecurityGroup'
});

• vpc - Use vpc created from vpc stack.
• allowAllOutbound - Allow outbound rules for access internet
• description - Description for security group
• securityGroupName - Define the security group name

Allow ssh access to bastion host

bastionSecurityGroup.addIngressRule(ec2.Peer.anyIpv4(), ec2.Port.tcp(22), 'SSH access');

lib/bastion-stack.ts

Get the vpc and bastionSecurityGroup from vpc and security stacks.

const { vpc, bastionSecurityGroup } = props;

Get profile from context variables

const profile = this.node.tryGetContext('profile');

Create bastion host instance in public subnet

const bastionHostLinux = new ec2.BastionHostLinux(this, 'BastionHostLinux', {  
  vpc: vpc,
  securityGroup: bastionSecurityGroup,
  subnetSelection: {
    subnetType: ec2.SubnetType.PUBLIC
  }
});

• vpc - Use vpc created from vpc stack.
• securityGroup - Use security group created from security stack.
• subnetSelection - Create the instance in public subnet.

Display commands for connect bastion host using ec2 instance connect

const createSshKeyCommand = 'ssh-keygen -t rsa -f my_rsa_key';
const pushSshKeyCommand = `aws ec2-instance-connect send-ssh-public-key --region ${cdk.Aws.REGION} --instance-id ${bastionHostLinux.instanceId} --availability-zone ${bastionHostLinux.instanceAvailabilityZone} --instance-os-user ec2-user --ssh-public-key file://my_rsa_key.pub ${profile ? `--profile ${profile}` : ''}`;
const sshCommand = `ssh -o "IdentitiesOnly=yes" -i my_rsa_key ec2-user@${bastionHostLinux.instancePublicDnsName}`;
        
new cdk.CfnOutput(this, 'CreateSshKeyCommand', { value: createSshKeyCommand });
new cdk.CfnOutput(this, 'PushSshKeyCommand', { value: pushSshKeyCommand });
new cdk.CfnOutput(this, 'SshCommand', { value: sshCommand});

Deploy all the stacks to your aws account.

cdk deploy '*'
or
cdk deploy '*' --profile your_profile_name

Use cases

Act as the jumpbox to access your private cloud resources via ec2 instance connect.

Follow the step below to access your bastion host via ec2 instance connect:

1. Generate ssh key pair in your local machine

   ssh-keygen -t rsa -f my_rsa_key

2. Push the ssh public key to your bastion host instance

   aws ec2-instance-connect send-ssh-public-key \
     --region <region_name>
     --instance-id <instance_id>
     --availability-zone <availability_zone>
     --instance-os-user ec2-user
     --ssh-public-key file://my_rsa_key.pub

3. Access your bastion host via ssh

   ssh -o "IdentitiesOnly=yes" -i my_rsa_key ec2-user@<public_dns_name_for_your_bastion_host>

Useful commands

NPM commands

• npm run build compile typescript to js
• npm run watch watch for changes and compile
• npm run test perform the jest unit tests

Toolkit commands

• cdk list (ls) Lists the stacks in the app
• cdk synthesize (synth) Synthesizes and prints the CloudFormation template for the specified stack(s)
• cdk bootstrap Deploys the CDK Toolkit stack, required to deploy stacks containing assets
• cdk deploy Deploys the specified stack(s)
• cdk deploy '*' Deploys all stacks at once
• cdk destroy Destroys the specified stack(s)
• cdk destroy '*' Destroys all stacks at once
• cdk diff Compares the specified stack with the deployed stack or a local CloudFormation template
• cdk metadata Displays metadata about the specified stack
• cdk init Creates a new CDK project in the current directory from a specified template
• cdk context Manages cached context values
• cdk docs (doc) Opens the CDK API reference in your browser
• cdk doctor Checks your CDK project for potential problems

Pricing

As this cdk stack will create bastion host instance using T3.nano, please refer the following link for pricing

• EC2 Pricing