AWS Security

AWS Security: Bastion Hosts, NAT Instances, and VPC Peering

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Amazon Web Services (AWS) provides a highly scalable cloud computing platform with the advantages of high availability and trustworthiness. AWS security is one of the prominent factors that drive the popularity and adoption of AWS solutions. AWS prioritizes the confidentiality and integrity of all the customer systems and data on AWS. As a result, AWS could earn and maintain the trust and confidence of customers in its services.

AWS allows companies to scale their infrastructure and applications dynamically. They have baked amazing security features into their services. To ensure that AWS services are properly configured as per the best practices, they provide many offerings. These are considered as the essential tools for AWS security and are required to understand well.

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Essential Tools for AWS Security

The prominence of various AWS security issues calls for immediate action to ensure 100% security for your systems and data. The following discussion would guide you through three essential tools for AWS cloud security. The primary highlights of the following discussion would be bastion hosts, NAT instances, and VPC peering. Let us find out more about their importance in safeguarding your AWS infrastructure. 

Bastion Hosts

The first entry in this discussion about AWS cloud security best practices is bastion hosts. Bastion hosts are instances which station within the public subnet, and access to Bastion hosts is possible through SSH or RDP. After establishing remote connectivity with the bastion host, it assumes the identity of a ‘jump’ server.

The bastion host then helps you log into other instances at deeper levels within the concerned VPC by leveraging SSH or RDP. With proper configuration by using Network ACLs (NACLs) and security groups, the bastion could help in serving as a bridge for your private instances through the internet. 

The requirement of a bastion host for AWS security depends on your needs. For example, if you need remote connectivity with private instances in your VPC across the public internet, then yes! One of the important practices for the design of bastion host for AWS infrastructure is to refrain from its use for any other purposes.

Designing the bastion host for an AWS infrastructure with scope for other purposes could lead to unwanted vulnerabilities in security. Therefore, better hardening of the operating system could provide exceptional results in terms of tighter security. The basic steps for the creation of a bastion host are as follows.

  • Launch an EC2 instance just like for any other instance.
  • Implementation of OS hardening according to requirements.
  • Establish proper security groups (SGs).
  • Implementation of either Remote Desktop Gateway for Windows connectivity or SSH-agent forwarding for Linux connectivity.
  • Deployment of an AWS bastion host in every Availability Zone you consider for use. 

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Security Groups in Bastion Hosts

Security groups are crucial elements for maintaining tight AWS security. In addition, security groups also play an important role in the functionality of bastion hosts. First of all, create a security group that can help in allowing bastion connectivity for existing private instances. The SG should accept only SSH or RDP inbound requests from bastion hosts across concerned Availability Zones (AZ).

This security group should be on all private instances that demand connectivity. The next security group that you create should be ideal for application to the bastion host. The restrictions on inbound and outbound traffic at the protocol level should be as high as possible. The inbound rule should accept SSH or RDP connections from specific IP addresses only.

The outbound connection rule should involve only SSH or RDP access to private instances of an AWS infrastructure. The best practice for achieving this is through populating the “Destination” field with the ID of the security group meant for private instances. 

One of the notable highlights of the AWS security services in the bastion host refers to the requirement of public and private key access for authentication of SSH and RDP connection. Connecting with the bastion host from a local machine is very easy because you could store the private key locally. On the other hand, logging into the private instances after connecting the bastion host can demand private keys on the bastion.

Therefore, you can face difficulties in the storage of private keys. Most important of all, you can risk your AWS security by storing private keys on remote instances. However, bastion hosts resolve this issue by providing SSH-agent forwarding and RDP connections to Linux instances and Windows instances, respectively. These two solutions take away the need for storage of private keys on the bastion host.

One of the promising highlights, in this case, is the facility of reliable AWS documentation for approaches on implementation of Windows Remote Desktop Gateway and SSH- agent forwarding. Finally, the deployment of a bastion in each public Availability Zone in use is imperative. Why? Because of the AZ hosting your bastion host becomes unavailable, then you can lose connectivity with your private instances in other Availability Zones. 

Also Read: How to grant access to AWS Resources to the third party via roles & external Id?

Updates to Bastion Host Functionality

AWS security best practices also imply that you should update your bastion hosts frequently for better security status. First of all, you could skip bastion hosts totally through the Session Manager in the AWS Systems Manager. As a result, you can connect with all private instances in a VPC with higher security. Most important of all, you would not need an intermediary bastion host or the other security-related dependencies such as key-pairs.

Another recommendation for leveraging the best of bastion host AWS security services is the use of EC2 Instance Connect. EC2 Instance Connect could help you in simplification of certain management aspects of bastion hosts. So, you can shun worries for the association of key-pair to a bastion host instance or addition of permanent user keys to authorized keys.

On the contrary, you can push keys for short intervals of time alongside using IAM policies for restricting access accordingly. As a result, you can witness a reduction in your audit and compliance footprint. The best practice for using Instance Connect refers to its use along with the AWS Lambda function for automation of the SG group config. As a result, you can ensure permissions for access from predefined IP address range of Instance Connect service. 

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NAT Instances

Another prominent mention in the AWS security services list is AWS NAT instances and NAT gateways. Network Address Transition (NAT) instance is similar to the bastion host and is evident as an EC2 instance living in your public subnet. On the other hand, NAT instance allows the outgoing connectivity of private instances with the internet. At the same time, NAT instance also blocks inbound traffic from the internet.

Various users configure the NAT instances for allowing private instances to access the internet for significant OS updates. The frequent patching of your OS is a crucial aspect of the maintenance of instance-level security. NAT Gateways are AWS managed NAT service with similar functionalities as NAT instances. Therefore, NAT Gateways tend to offer better availability and bandwidth, albeit with limited configuration and administration for AWS security. 

The process of creating and launch NAT instances for AWS security is as follows.

  • Create a Security group for application to the NAT.
  • Choose a pre-defined AMI and implement its configuration like any other EC2 instance.
  • Establish the correct routing.

After launching NAT, you should focus on disabling the source or destination checks. You can achieve this by right-clicking on the NAT instance in the AWS Console. Now, choose the option of “Networking” and then “Change Source/Dest. Check”. Click on the “Yes” button and then “Disable” for confirmation.

Creating a security group for your NAT is one of the important AWS security best practices. You should ensure permissions for allowing inbound traffic from private instances through HTTPS (443) and HTTP (80) ports for allowing OS and software updates. The outbound rule must also have an open destination for 80 and 443 ports also. The most important concern is to ensure restrictions on connections starting from the internet from reaching private instances. 

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AWS VPC Peering

Now, the final entry in our discussion and a prominent one among the AWS security services list is AWS VPC Peering. AWS VPC (Virtual Private Cloud) peering helps in the connection of two VPCs as a single network. VPC peering utilizes the AWS network infrastructure for sharing resources among VPCs.

As a result, there is no need to route data through a VPN connection or the internet. AWS VPC peering could thus help in ensuring a comprehensive and highly secure shared environment with limited external exposure. Peered VPCs interact through the private CIDR blocks. So, it is important that two different VPCs should not have similar CIDR address ranges.

Furthermore, you could not just reference a security group directly from one VPC to the other. On the other hand, you have to input a specific IP address or CIDR block in the Source/Destination section of SG rules. AWS VPC peering is one of the credible instruments for AWS security by providing excellent and trusted secure connections between VPCs. 

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Final Words

The landscape of AWS security is spread out extensively across a wider assortment of products, services, and tools. So, the above-mentioned discussion shows that bastion hosts, NAT instances, and VPC peering could be promising instruments for AWS security. For example, the bastion host enables secure primary connection for accessing private instances through the internet. In addition, VPC peering helps in establishing secure connectivity and file sharing privileges between VPCs.

Furthermore, NAT instances help in availing access to essential software updates alongside blocking access to external traffic. Therefore, we clearly note that bastion hosts, NAT instances, and VPC peering offer the perfect tools for keeping your data within your network. In addition, these tools also provide flexibility for the management of secure data. So, the security posture of AWS seems to be very strong, doesn’t it?

If you are an AWS security specialist, it is required that you should have enough knowledge about these tools for AWS security. Also, it is recommended that you should validate your knowledge and expertise with the AWS Security Specialty certification. Check out our AWS Certified Security Specialty training course and prepare well to become a certified professional!

About Pavan Gumaste

Pavan Rao is a programmer / Developer by Profession and Cloud Computing Professional by choice with in-depth knowledge in AWS, Azure, Google Cloud Platform. He helps the organisation figure out what to build, ensure successful delivery, and incorporate user learning to improve the strategy and product further.

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