Building a secure cloud environment on Amazon Web Services requires more than simply launching servers and hoping for the best. As organizations move sensitive workloads to the cloud, the network architecture surrounding those workloads becomes just as important as the applications themselves. Three components that frequently come up in discussions about secure AWS network design are bastion hosts, NAT gateways, and VPC interconnection methods, each serving a distinct purpose in keeping resources both accessible to authorized users and protected from unwanted exposure to the broader internet.
These three concepts often get grouped together because they all deal with controlling how traffic flows into, out of, and between private network segments. A bastion host provides a secure entry point for administrators who need to access private resources, a NAT gateway allows private resources to reach the internet for updates and external services without being directly reachable from outside, and VPC interconnection methods allow separate virtual networks to communicate with each other in controlled ways. Understanding how these pieces fit together, and when each one is appropriate, forms a foundational part of designing AWS environments that balance security with practical usability.
Understanding Virtual Private Clouds
Before diving into bastion hosts and gateways, it helps to understand the foundation upon which these components operate, which is the virtual private cloud itself. A VPC represents an isolated section of AWS infrastructure where an organization can launch resources within a logically isolated network that they control, including defining IP address ranges, creating subnets, and configuring route tables and network gateways.
Within a VPC, subnets are typically categorized as either public or private, based on whether they have a route to an internet gateway. Public subnets can have resources that are directly reachable from the internet, while private subnets contain resources that should not be directly exposed, such as databases or internal application servers. This separation forms the basis for why tools like bastion hosts and NAT gateways become necessary, since organizations need ways to manage and update resources in private subnets without exposing those resources directly to the internet.
The Purpose Of Bastion Hosts
A bastion host, sometimes called a jump box or jump server, serves as a single, hardened point of entry that administrators use to access resources within private subnets. Rather than exposing every server in a private subnet to direct internet access for administrative purposes, organizations place a single bastion host in a public subnet, configure strict security controls around it, and require administrators to connect through this host before reaching anything in the private network.
This approach significantly reduces the attack surface of an environment, since instead of having multiple servers each potentially exposed to remote access attempts, only the bastion host itself needs to be carefully monitored and secured. Security groups associated with the bastion host typically restrict access to specific IP addresses or ranges, often corresponding to an organization’s office network or VPN endpoints, ensuring that even this single point of entry is not openly accessible to the entire internet. Once an administrator connects to the bastion host, they can then connect onward to resources within private subnets, with the bastion host acting as an intermediary that funnels and controls this administrative access.
Configuring Bastion Host Security
Simply placing a bastion host in a public subnet does not automatically make an environment secure, since the bastion host itself becomes an attractive target precisely because it provides a path into otherwise protected resources. Proper configuration involves several layers of protection working together to minimize risk associated with this single point of entry.
At the network level, security groups should restrict inbound access to only the specific protocols and source addresses that legitimate administrators would use, rather than allowing broad access from anywhere. At the host level, keeping the operating system updated, disabling unnecessary services, and implementing strong authentication mechanisms, such as key-based authentication rather than passwords, further reduces risk. Many organizations also implement session logging on bastion hosts, recording commands executed during administrative sessions, which provides an audit trail that can be valuable both for security monitoring and for troubleshooting issues after the fact, since having a record of what changes were made and by whom can prove invaluable when investigating unexpected behavior in private resources.
Alternatives To Traditional Bastions
While bastion hosts have long been a standard approach for accessing private resources, AWS has introduced services that provide similar functionality with potentially reduced operational overhead. Systems Manager Session Manager, for example, allows administrators to connect to instances without requiring an open inbound port for SSH or RDP access, instead using AWS APIs and IAM permissions to control and audit access.
This approach eliminates the need to manage a separate bastion host entirely in some architectures, since the Session Manager agent running on instances can establish connections through AWS’s own infrastructure rather than requiring direct network connectivity from an administrator’s location. Organizations evaluating their approach to administrative access often find that combining traditional bastion hosts for certain use cases with newer approaches like Session Manager for others provides flexibility, though transitioning entirely away from bastion hosts may require updates to existing tooling, scripts, and team workflows that have been built around traditional jump server access patterns over time.
How NAT Gateways Function
While bastion hosts address inbound access to private resources, NAT gateways address the opposite direction, allowing resources within private subnets to initiate outbound connections to the internet without being directly reachable from the internet themselves. This matters because private resources, such as application servers, often need to download software updates, access external APIs, or communicate with services outside the VPC, even though these same resources should never receive unsolicited inbound connections from the internet.
A NAT gateway sits within a public subnet and translates outbound traffic from private subnet resources, presenting a single public IP address for all outbound traffic originating from those private resources. When responses come back from external services, the NAT gateway routes them back to the originating resource within the private subnet, maintaining the one-way nature of this relationship where private resources can reach out but external parties cannot initiate connections inward through this same path.
Comparing NAT Gateways And Instances
Before managed NAT gateways became available, organizations often implemented NAT functionality using EC2 instances configured to perform network address translation, sometimes called NAT instances. While this approach still works and remains relevant for certain specialized use cases, managed NAT gateways have become the preferred approach for most organizations due to reduced operational burden.
NAT gateways are managed services that automatically scale to handle traffic and do not require patching, monitoring, or maintenance the way a NAT instance running on EC2 would. This reduces the operational overhead significantly, though it comes with a cost structure based on data processed through the gateway, which can become a meaningful expense for environments with high volumes of outbound traffic. Organizations with very specific requirements, such as needing to run additional software on the NAT device itself or requiring more granular control over the underlying configuration, sometimes still choose NAT instances despite the additional management burden, but for most standard use cases, the operational simplicity of managed NAT gateways outweighs the cost considerations for all but the highest-traffic environments.
Placement And High Availability
NAT gateways must be placed within public subnets, since they require a route to the internet gateway to function. For environments spanning multiple availability zones, which is common practice for production workloads to ensure resilience against zone-level failures, organizations typically deploy a NAT gateway in each availability zone rather than relying on a single NAT gateway for the entire VPC.
This multi-zone approach ensures that if one availability zone experiences issues, private subnet resources in other zones can continue routing outbound traffic through their own zone’s NAT gateway without depending on a NAT gateway in a different zone that might be affected by whatever issue is occurring. While this approach increases costs compared to a single NAT gateway, the improved resilience often justifies this additional expense for production environments where availability matters significantly, since the alternative, having private resources across multiple zones depend on a NAT gateway in just one zone, creates a single point of failure that undermines the broader multi-zone architecture an organization might have otherwise carefully designed.
Connecting Multiple VPCs Together
As organizations grow, they often find themselves managing multiple VPCs, whether due to different business units, separate environments for development and production, or acquisitions that bring previously separate AWS environments into a single organization. In these situations, resources within different VPCs sometimes need to communicate with each other, requiring some form of VPC interconnection.
Several approaches exist for connecting VPCs together, each with different characteristics in terms of scalability, cost, and complexity. The right choice depends on factors like how many VPCs need to be connected, whether connectivity needs to span different AWS accounts or regions, and how complex the routing requirements between these networks need to be. Understanding the available options helps organizations choose an approach that meets their current needs while remaining adaptable as their environment continues to grow and evolve over time.
VPC Peering Explained
VPC peering represents one of the simplest ways to connect two VPCs, establishing a direct network connection between them that allows resources in either VPC to communicate with resources in the other as if they were part of the same network, provided appropriate routing and security group configurations are in place. This connection does not involve any intermediate gateway device, instead relying on AWS’s underlying network infrastructure to route traffic directly between the peered VPCs.
While VPC peering works well for connecting a small number of VPCs, it does not scale efficiently to large numbers of VPCs, since peering connections are not transitive, meaning that if VPC A is peered with VPC B, and VPC B is peered with VPC C, resources in VPC A cannot automatically communicate with resources in VPC C through this chain. Organizations with many VPCs that all need to communicate with each other would need to establish individual peering connections between every pair of VPCs, which becomes increasingly complex to manage as the number of VPCs grows, since the number of required connections increases rapidly with each additional VPC added to the environment.
Transit Gateway For Complex Networks
For organizations managing numerous VPCs that need to communicate with each other, AWS Transit Gateway provides a more scalable solution by acting as a central hub that VPCs connect to, rather than requiring direct connections between every pair of VPCs. Each VPC establishes a single connection to the transit gateway, and the transit gateway then handles routing traffic between all connected VPCs according to configured route tables.
This hub and spoke model dramatically simplifies the connectivity model for organizations with many VPCs, since adding a new VPC to the network only requires connecting that single VPC to the existing transit gateway, rather than establishing new connections to every other VPC in the environment. Transit gateways also support connections to on-premises networks through VPN or dedicated network connections, making them valuable not just for connecting VPCs to each other but also for integrating cloud environments with existing data center networks as part of a broader hybrid infrastructure strategy.
Site To Site VPN Connections
Organizations that need to connect their AWS environment to an on-premises network, such as a corporate data center or office network, often use site to site VPN connections as a way to establish this connectivity without requiring dedicated physical network infrastructure. These connections use encrypted tunnels over the internet to connect a customer’s network equipment to AWS, allowing resources on both sides to communicate as if they were part of the same network.
While VPN connections provide a relatively quick and cost-effective way to establish hybrid connectivity, they do rely on internet connectivity for the underlying tunnel, which means performance and reliability depend partly on the quality of internet connectivity available at the on-premises location. For organizations that need more consistent performance or higher bandwidth than VPN connections over the internet can reliably provide, dedicated network connections offer an alternative that bypasses the public internet for this connectivity entirely.
Dedicated Network Connections
AWS Direct Connect provides a way to establish a dedicated network connection between an on-premises environment and AWS, bypassing the public internet entirely for this traffic. This approach typically provides more consistent performance and can support higher bandwidth requirements compared to VPN connections, making it attractive for organizations with significant amounts of traffic flowing between their own infrastructure and AWS.
Setting up these dedicated connections involves working with network providers to establish physical connectivity to AWS infrastructure, which means implementation timelines tend to be longer compared to the relatively quick setup process for VPN connections. Organizations often use VPN connections as an interim solution while dedicated connections are being established, or as a backup connectivity method that provides redundancy if a dedicated connection experiences issues, ensuring that hybrid connectivity remains available even if one connection method encounters problems.
Security Considerations For Interconnection
Whenever VPCs are connected to each other or to on-premises networks, security considerations become particularly important, since these connections potentially expand the attack surface of an environment by creating new paths through which traffic can flow. Security groups, network access control lists, and route table configurations all play important roles in ensuring that interconnection methods provide necessary connectivity without inadvertently exposing resources that should remain isolated.
Organizations should carefully consider what traffic actually needs to flow between connected networks, configuring routing and security rules to allow only this necessary traffic rather than broadly opening up connectivity between entire network ranges. This principle of least privilege applies just as much to network interconnection as it does to other aspects of security, since overly permissive routing between connected VPCs or networks can inadvertently create paths that bypass other security controls an organization has carefully implemented elsewhere in their environment.
Monitoring And Logging Network Traffic
Regardless of which combination of bastion hosts, NAT gateways, and interconnection methods an organization implements, monitoring and logging network traffic provides essential visibility into how these components are being used and helps identify potential security issues or unexpected traffic patterns. VPC flow logs capture information about traffic flowing through network interfaces, providing data that can be analyzed to understand normal traffic patterns and identify anomalies that might indicate security concerns.
For bastion hosts specifically, monitoring login attempts and session activity helps identify potential unauthorized access attempts, while for NAT gateways, monitoring data transfer volumes can help identify unexpected spikes that might indicate compromised resources generating unusual outbound traffic. Establishing baseline expectations for normal traffic patterns across these different components, then configuring alerts for significant deviations from these baselines, helps organizations detect potential issues more quickly than relying solely on reactive investigation after problems have already caused noticeable impact.
Bringing These Components Together
In practice, a well-designed AWS network architecture often combines bastion hosts, NAT gateways, and appropriate VPC interconnection methods together as part of a cohesive overall design rather than implementing each component in isolation. A typical pattern might involve a VPC with both public and private subnets across multiple availability zones, with a bastion host or alternative access method in the public subnet providing controlled administrative access, NAT gateways in each availability zone allowing private resources to reach external services, and a transit gateway connecting this VPC to other VPCs within the organization as well as to on-premises networks through dedicated connections or VPN.
This combination addresses the fundamental network security challenge of allowing necessary connectivity, whether for administrators needing access, private resources needing outbound internet connectivity, or different parts of an organization’s infrastructure needing to communicate, while minimizing unnecessary exposure that could create security vulnerabilities. Each component plays a specific role within this broader picture, and understanding how they work together, rather than viewing them as entirely separate concerns, helps organizations design network architectures that are both secure and practical for their teams to work with on a daily basis.
Final Thoughts
Building secure network architecture on AWS requires thinking carefully about how different components work together to balance security with usability. Bastion hosts provide controlled administrative access without exposing every resource to potential remote access attempts, NAT gateways allow private resources to reach external services without becoming directly reachable themselves, and VPC interconnection methods enable communication between different parts of an organization’s infrastructure while maintaining appropriate boundaries and controls. None of these components exist in isolation, and the most effective security architectures consider how these pieces interact with each other rather than treating each as a separate checkbox to satisfy during initial setup.
As organizations grow and their AWS environments become more complex, revisiting these network design decisions periodically becomes important, since architectures that worked well for a smaller environment with fewer VPCs and simpler connectivity requirements might not scale efficiently as the organization adds more VPCs, more on-premises connectivity needs, or more administrative access requirements across larger teams. What started as a single VPC with a simple bastion host and one NAT gateway might eventually need to evolve into a more complex architecture involving transit gateways connecting numerous VPCs, multiple redundant connections to on-premises infrastructure, and potentially newer access methods that reduce reliance on traditional bastion hosts altogether.
Ultimately, the goal of implementing these various components is not security for its own sake but rather creating an environment where teams can work efficiently and resources can communicate as needed, while ensuring that the attack surface remains as small as practically possible given the organization’s actual requirements. Security measures that create excessive friction for legitimate use often lead to workarounds that undermine the security goals these measures were meant to achieve, so finding the right balance matters as much as implementing the components themselves. Organizations that approach network security architecture thoughtfully, considering not just individual components but how those components work together within the broader context of their specific needs, tend to build environments that remain both secure and manageable as they continue to grow and evolve over time, avoiding the common trap of either excessive complexity that nobody fully understands or oversimplified designs that fail to address genuine security requirements as the organization scales.