@moia-oss/bastion-host-forward

Bastion Host Forward

This is a CDK Library providing custom bastion host constructs for connecting to several AWS data services. When building secure infrastructure, we face the problem that the data layer is only accessible from inside the VPC. These Bastion Hosts close the gap and let you interact with the data layer as they would be hosted on your machine.

Currently the following AWS Services are supported:

AWS Service	CDK Construct
Aurora Serverless	BastionHostAuroraServerlessForward
Redis	BastionHostRedisForward
Redshift	BastionHostRedshiftForward
RDS	BastionHostRDSForward

V1 DISCLAIMER

We introduced v1.0.0 recently, which now relies on v2 of CDK. This introced an incompability, because they don't offer a L2 Construct for Redshift anymore. This is why we cant offer the BastionHostRedshiftForward Construct anymore. We would need to accept a CFN L1 Construct instead, but we didn't allow this for the BastionHostRedisForward as well. Instead we decided to rename the BastionHostRedisForward to GenericBastionHostForward, which needs only the endpoint address and the port of the data store to be able to forward connections.

With the new GenericBastionHostForward you are still able to forward connections to Redis and Redshift and also every other data store in AWS, which we don't support specifically so far.

Technical details

The bastion hosts are extensions of the official BastionHostLinux CDK construct, which allows connecting to the bastion host and from there connect to the data layer.

These constructs additionally install and configure HAProxy to forward the endpoint of the chosen data store. They also have the SSM Agent to the bastion host, so you can connect via the AWS Session Manager. Connecting to a bastion host via the AWS Session Manager brings a couple of benefits:

• No management of SSH Keys anymore
• AWS IAM defines who is able to connect to the bastion host
• Bastion Hosts don't need to be hosted in public subnets anymore
• Easy port forwarding with a single command

The combination of having a local port forward via SSM Session Manager and the HAProxy on the bastion host itself let you interact with the data layer as they would be on your machine. This means you can connect to them via localhost: and also use visual tools like DataGrip or MySQL Workbench to interact with the data store in AWS. The following graphic illustrates the described procedure on the example of RDS:

Setup

First of all you need to include this library into your project for the language you want to deploy the bastion host with

Javascript/Typescript

For Javascript/Typescript the library can be installed via npm:

npm install @moia-oss/bastion-host-forward

Python

For python the library can be installed via pip:

pip install moia-dev.bastion-host-forward

Examples

The following section includes some examples in supported languages how the Bastion Host can be created for different databases.

Bastion Host for RDS in Typescript

A minimal example for creating the RDS Forward Construct, which will be used via username/password could look like this snippet:

import * as cdk from '@aws-cdk/core';
import { SecurityGroup, Vpc } from '@aws-cdk/aws-ec2';
import { DatabaseInstance } from '@aws-cdk/aws-rds';
import { BastionHostRDSForward } from '@moia-oss/bastion-host-forward';

export class BastionHostPocStack extends cdk.Stack {
  constructor(scope: cdk.App, id: string, props?: cdk.StackProps) {
    super(scope, id, props);

    const vpc = Vpc.fromLookup(this, 'MyVpc', {
      vpcId: 'vpc-0123456789abcd'
    });

    const securityGroup = SecurityGroup.fromSecurityGroupId(
      this,
      'RDSSecurityGroup',
      'odsufa5addasdj',
      { mutable: false }
    );

    const rdsInstance = DatabaseInstance.fromDatabaseInstanceAttributes(
      this,
      'MyDb',
      {
        instanceIdentifier: 'abcd1234geh',
        instanceEndpointAddress: 'abcd1234geh.ughia8asd.eu-central-1.rds.amazonaws.com',
        port: 5432,
        securityGroups: [securityGroup]
      }
    );

    new BastionHostRDSForward(this, 'BastionHost', {
      vpc: vpc,
      rdsInstance: rdsInstance,
      name: 'MyBastionHost',
    });

If the RDS is IAM Authenticated you also need to add an iam_user and rdsResourceIdentifier to the BastionHostRDSForward:

...
new BastionHostRDSForward(this, 'BastionHost', {
  vpc: vpc,
  rdsInstance: rdsInstance,
  name: 'MyBastionHost',
  iamUser: 'iamusername',
  rdsResourceIdentifier: 'db-ABCDEFGHIJKL123'
});

This will spawn a Bastion Host in the defined VPC. You also need to make sure that IPs from within the VPC are able to connect to the RDS Database. This needs to be set in the RDS's Security Group. Otherwise the Bastion Host can't connect to the RDS.

Bastion Host for a generic data store on AWS (Redis, Redshift etc.)

Typescript

A minimal example for creating the Generic Forward Construct, which will be used via username/password could look like this snippet. In this case we forward a connection to a RedShift instance, but this can also be a Redis Node or any other data store on AWS. Instead of passing the complete L2 construct and letting the library extract the necessary properties, the client is passing them directly to the construct:

import * as cdk from '@aws-cdk/core';
import { GenericBastionHostForward } from '@moia-oss/bastion-host-forward';
import { SecurityGroup, Vpc } from '@aws-cdk/aws-ec2';
import { Cluster } from '@aws-cdk/aws-redshift';

export class PocRedshiftStack extends cdk.Stack {
  constructor(scope: cdk.Construct, id: string, props?: cdk.StackProps) {
    super(scope, id, props);

    const vpc = Vpc.fromLookup(this, 'MyVpc', {
      vpcId: 'vpc-12345678',
    });

    const securityGroup = SecurityGroup.fromSecurityGroupId(this, 'BastionHostSecurityGroup', 'sg-1245678', {
      mutable: false,
    });

    const redshiftCluster = Cluster.fromClusterAttributes(this, 'RedshiftCluster', {
      clusterName: 'myRedshiftClusterName',
      clusterEndpointAddress: 'myRedshiftClusterName.abcdefg.eu-central-1.redshift.amazonaws.com',
      clusterEndpointPort: 5439,
    });

    new GenericBastionHostForward(this, 'BastionHostRedshiftForward', {
      vpc,
      securityGroup,
      name: 'MyRedshiftBastionHost',
      address: redshiftCluster.clusterEndpointAddress,
      port: redshiftCluster.clusterEndpointPort,
    });
  }
}

Python

from aws_cdk import core as cdk
from aws_cdk import aws_redshift
from aws_cdk import aws_ec2
from moia_dev import bastion_host_forward


class PocRedshiftStack(cdk.Stack):

    def __init__(self, scope: cdk.Construct, construct_id: str, **kwargs) -> None:
        super().__init__(scope, construct_id, **kwargs)
        vpc = aws_ec2.Vpc.from_lookup(
            self,
            "vpc",
            vpc_id="vpc-12345678"
        )
        security_group = aws_ec2.SecurityGroup.from_security_group_id(
            self,
            "sec_group", "sg-12345678"
        )
        redshift_cluster = aws_redshift.Cluster.from_cluster_attributes(
            self,
            "cluster",
            cluster_name="myRedshiftClusterName",
            cluster_endpoint_address="myRedshiftClusterName.abcdefg.eu-central-1.redshift.amazonaws.com",
            cluster_endpoint_port=5439
        )

        bastion_host_forward.GenericBastionHostForward(
            self,
            "bastion-host",
            name="my-bastion-host",
            security_group=security_group,
            address: redshift_cluster.cluster_endpoint_address,
            port: redshift_cluster.cluster_endpoint_port,
            vpc=vpc
        )

Bastion Host for Aurora Serverless

import * as cdk from '@aws-cdk/core';
import { SecurityGroup, Vpc } from '@aws-cdk/aws-ec2';
import { ServerlessCluster } from '@aws-cdk/aws-rds';
import { BastionHostAuroraServerlessForward } from '@moia-oss/bastion-host-rds-forward';

export class BastionHostPocStack extends cdk.Stack {
  constructor(scope: cdk.App, id: string, props?: cdk.StackProps) {
    super(scope, id, props);

    const vpc = Vpc.fromLookup(this, 'MyVpc', {
      vpcId: 'vpc-0123456789abcd'
    });

    const securityGroup = SecurityGroup.fromSecurityGroupId(
      this,
      'AuroraSecurityGroup',
      'odsufa5addasdj',
      { mutable: false }
    );

    const serverlessCluster = ServerlessCluster.fromServerlessClusterAttributes(
      this,
      'Aurora',
      {
        clusterIdentifier: 'my-cluster',
        port: 3306,
        clusterEndpointAddress: 'my-aurora.cluster-abcdef.eu-central-1.rds.amazonaws.com',
        securityGroups: [securityGroup]
      }
    );

    new BastionHostAuroraServerlessForward(this, 'BastionHost', {
      vpc,
      serverlessCluster,
    });

Deploying the Bastion Host

When you setup the Bastion Host for the Database you want to connect to, you can now go forward to actually deploy the Bastion Host:

cdk deploy

When the EC2 Instance for you Bastion Host is visible you can continue with the setup of the Session-Manager Plugin on your Machine

Install the Session-Manager Plugin for AWS-CLI

You are also able to connect to the Bastion Host via the AWS Web Console. For this go to AWS Systems Manager -> Session Manager -> choose the newly created instance -> click on start session.

But overall it's a much more comfortable experience to connect to the Bastion Session Manager Plugin. On Mac OSX you can get it via homebrew for example:

brew install --cask session-manager-plugin

For Linux it should also be available in the respective package manager. Also have a look at the official installation instructions from AWS

Forward the connection to your machine

The Session Manager offers a command to forward a specific port. On the Bastion Host a HAProxy was installed which forwards the connection on the same port as the specified service. Those are by default:

• RDS MySQL: 3306
• RDS PostgreSQL: 5432
• Redis: 6739
• Redshift: 5439

In the following example, we show how to forward the connection of a PostgreSQL database. To forward the connection to our machine we execute the following command in the shell:

aws ssm start-session \
    --target <bastion-host-id> \
    --document-name AWS-StartPortForwardingSession \
    --parameters '{"portNumber": ["5432"], "localPortNumber":["5432"]}'

This creates a port forward session on the defined localPortNumber. The target is the id of the bastion host instance. This will be output automatically after deploying the bastion host. The portNumber must be the same as the RDS Port.

Now you would be able to connect to the RDS as it would run on localhost:5432.

Note

In the example of a MySQL running in Serverless Aurora, we couldn't connect to the database using localhost. If you face the same issue, make sure to also try to connect via the local IP 127.0.0.1.

Example with the MySQL CLI:

mysql -u <username> -h 127.0.0.1 -p

Additional step if you are using IAM Authentication on RDS

If you have an IAM authenticated RDS, the inline policy of the bastion host will be equipped with access rights accordingly. Namely it will get rds:* permissions on the RDS you provided and it also allows rds-db:connect with the provided iamUser.

Most of the steps you would perform to connect to the RDS are the same, since it wouldn't be in a VPC.

First you generate the PGPASSWORD on your local machine:

export
PGPASSWORD="$(aws rds generate-db-auth-token
--hostname=<rds endpoint> --port=5432
--username=<iam user> --region <the region of the rds>)"

You also need to have the RDS certificate from AWS, which you can download:

wget https://s3.amazonaws.com/rds-downloads/rds-ca-2019-root.pem

There is now an additional step needed, because the certificate checks against the real endpoint name during the connect procedure. Therefore we need to add an entry to the /etc/hosts file on our machine:

echo "127.0.0.1  <rds endpoint>" >> /etc/hosts

Now you can connect to the IAM authenticated RDS like this:

psql "host=<rds endpoint> port=5432 dbname=<database name> user=<iamUser> sslrootcert=<full path to downloaded cert> sslmode=verify-ca"

For a full guide on how to connect to an IAM authenticated RDS check out this guide by AWS