Test connectivity (for example, Route Analyzer, Reachability Analyzer, tooling)

Can you explain what AWS Reachability Analyzer is and how it can assist you in troubleshooting connectivity issues in your VPC?

AWS Reachability Analyzer is a tool within AWS’s VPC offering that helps you verify the network reachability between two endpoints in your AWS environment. It simplifies the troubleshooting process by enabling you to test reachability between Elastic Network Interfaces (ENIs), instances, subnets, and internet gateways. It generates a hop-by-hop analysis of the potential paths, and reports whether the desired connectivity is possible or not. If not, it identifies the configuration changes needed for remediation.

What is an AWS Route Analyzer, and in what scenarios would you use it as opposed to the Reachability Analyzer?

AWS Route Analyzer is not a specific AWS tool; rather, it is a common term that may refer to checking routes in the AWS Transit Gateway Network Manager. The use of routing analytics is instrumental when managing and monitoring a global network. The tool provides route analysis in complex environments with multiple connected VPCs, VPNs, and Direct Connect connections. Compared to AWS Reachability Analyzer, which troubleshoots VPC endpoint reachability, the Route Analyzer functionality within the Transit Gateway Network Manager is best for analyzing and optimizing routes on a more macro scale, across a multi-region, multi-account AWS environment.

What are the prerequisites for utilizing the AWS Reachability Analyzer?

To use AWS Reachability Analyzer, you need an AWS account, appropriate IAM permissions, and network resources such as VPCs, subnets, and route tables already set up. The source and destination between which you wish to assess reachability must be part of your account, and those resources need to be associated with an AWS Transit Gateway if you are testing connectivity across peering connections.

Can you describe the difference between a stateful and stateless rule, and how that impacts connectivity analysis?

A stateful rule, as used in AWS Network ACLs and security groups, remembers the state of a connection and automatically allows return traffic from a connection that was initiated. On the other hand, a stateless rule, such as those in network ACLs, does not track connection states and requires rules to explicitly allow both outbound and inbound traffic. In connectivity analysis, this distinction impacts how you interpret results because you need to make sure both directions of traffic are permitted in a stateless environment, while in a stateful context, you only need to consider the initial traffic direction.

What are some common connectivity issues that AWS Reachability Analyzer can help identify?

AWS Reachability Analyzer can help identify common connectivity issues such as incorrect route table entries, misconfigured network ACLs or security groups, absent or incorrect VPC peering connections, and issues with transit gateway attachments or route tables. It does not, however, resolve problems related to DNS resolution or external networks that AWS has no control over.

When performing a connectivity analysis, what AWS-specific considerations should you take into account, compared to on-premises environments?

In AWS, you should consider the underlying managed services and inherent characteristics of the AWS network, such as the implicit router that connects subnets within a VPC, the role of internet gateways for public connectivity, the use of NAT gateways/NAT instances for internet access from private subnets, and the specific nuances of AWS security group and network ACL behavior. AWS-managed networking constructs can behave differently and may have different limitations than on-premises networking equipment, so understanding these differences is crucial when analyzing connectivity in AWS.

How does AWS Reachability Analyzer aid in compliance and auditing tasks?

AWS Reachability Analyzer can assist in compliance and auditing by providing documentation of the tested network paths and evidencing whether network configurations are aligned with the organization’s compliance requirements. It helps validate that the required connectivity paths are open, while unnecessary paths are closed, ensuring adherence to the principle of least privilege.

Can AWS Reachability Analyzer test connectivity to endpoints outside of the AWS network, like a corporate data center or an on-premises environment?

No, AWS Reachability Analyzer cannot directly test connectivity to endpoints outside of AWS. It is designed to assess reachability within the AWS network, including VPCs, AWS Transit Gateway, and VPN connections. For hybrid scenarios, it can indicate if traffic is successfully reaching a VPN endpoint or a Direct Connect location, but you would need additional on-premises tooling to test connectivity from that point onward.

If the AWS Reachability Analyzer indicates that a particular path is not reachable, what are some remediation steps you can take?

If a path is not reachable, the remediation steps can include reviewing and modifying route table entries to ensure correct routing, adjusting network ACL and security group rules to permit relevant traffic, establishing or configuring VPC peering or transit gateways as needed, and checking configurations of any involved NAT gateways, VPN connections, or Direct Connect links for proper setup and operational status.

How might you use tags and AWS Resource Grouping features in conjunction with AWS Reachability Analyzer to enhance your analysis?

You can use tags to organize and categorize your AWS resources which can be particularly helpful when analyzing complex networks with many components. AWS Resource Grouping allows you to create collections of resources that share common tags. You can then use AWS Reachability Analyzer to test connectivity within these specific groups, which can simplify troubleshooting and ensure that the analysis is consistently applied to the correct resources within the defined operational boundaries of a project or environment.

Are there any limitations of the AWS Reachability Analyzer that one should be aware of when testing connectivity?

Yes, there are limitations to what AWS Reachability Analyzer can do. For example, it cannot test reachability to or from endpoints not managed by AWS, such as user devices or on-premises servers, and there are limits on the number of active and completed path analyses. Furthermore, it does not analyze performance issues or the actual data transmission, only potential connectivity based on network configuration.

Could you explain a scenario where you would need to troubleshoot connectivity for a hybrid cloud architecture using both AWS and on-premises resources?

In a hybrid cloud architecture, you may encounter a scenario where an application running on AWS needs to access a database hosted on-premises. If there are connectivity issues, you would use tools like AWS Reachability Analyzer to check the AWS side of the network up to the VPN or Direct Connect endpoint. Next, you’d ensure that your on-premises firewalls, routers, or SD-WAN solutions are configured correctly to allow traffic from AWS. Additionally, you should verify that the necessary routing rules and security settings are in place on both ends to facilitate seamless communication between AWS and the on-premises environment.