Testing and validating connectivity between environments

Describe the steps you would take to test the connectivity between an on-premises environment and an Amazon VPC using AWS Direct Connect.

To test connectivity between an on-premises environment and an Amazon VPC using AWS Direct Connect, I would first ensure that the Direct Connect connection is in the ‘Available’ state. Then, I would configure the on-premises router with the appropriate VLAN and BGP sessions as per AWS requirements. Next, I would verify that the Virtual Interface is up and that the BGP peering session is established. After that, I’d use tools such as ‘ping’ or ‘traceroute’ for initial connectivity tests, and ensure proper route propagation in both environments to allow traffic flow.

What AWS tool can you use to check for possible network ACL and security group configuration issues affecting connectivity?

The AWS tool I can use is the VPC Reachability Analyzer. This tool helps to troubleshoot connectivity issues caused by misconfigured network ACLs, security groups, route tables, and other VPC components by analyzing the network path between a source and a destination.

Explain how you would validate connectivity between two VPCs set up with a VPC peering connection.

To validate connectivity between two VPCs with VPC peering, I would first check the peering connection status to ensure it’s ‘Active.’ Then I would verify that the route tables in both VPCs contain routes to each other’s CIDR blocks via the peering connection. After that, I’d ensure that there are no overlapping IP address ranges and that network ACLs and security groups allow the required traffic. Finally, I would conduct a ping or application-specific test between instances in both VPCs.

How would you test connectivity from an EC2 instance to an RDS instance that are in separate VPCs with a peering connection?

First, I would verify the VPC peering is active and the correct routes are in place on both VPCs’ route tables pointing to each other. Then, I’d check the security groups and network ACLs to ensure that they allow the specific traffic for the database (like the appropriate port for MySQL or PostgreSQL). Lastly, I would connect to the EC2 instance and attempt to connect to the RDS instance using the database client, confirming communication over the peering connection.

Discuss the method you would use to validate the network bandwidth performance between EC2 instances in different availability zones.

To validate network bandwidth performance between EC2 instances in different availability zones, I would use built-in tools like Amazon CloudWatch to monitor metrics like NetworkIn and NetworkOut. Apart from this, I can perform tests using network performance testing tools like iperf or netperf. I would ensure that instances are of a type that supports Enhanced Networking for the best performance and that they are in the same region to use the low-latency network provided by AWS between different availability zones.

What steps would you take to test connectivity to an internet-facing ELB from an external network?

To test connectivity to an internet-facing Elastic Load Balancer (ELB) from an external network, I’d first confirm that the ELB is correctly configured with a listener for the desired protocol and port. Next, I would make sure that the associated security groups and network ACLs allow inbound traffic on the appropriate ports from my source network. Then, I’d use a tool such as ‘curl’ or a web browser to send a request to the ELB DNS name and verify that I can receive a response from one of the backend instances.

How would you troubleshoot an issue where EC2 instances in a VPC cannot access the Internet through a NAT gateway?

To troubleshoot EC2 instances that cannot access the Internet through a NAT gateway, I would check several key areas: First, ensure the NAT gateway is in the ‘Available’ state and has an Elastic IP address attached. Next, verify the route table associated with the private subnet directs internet-bound traffic to the NAT gateway. After that, check that the security groups and network ACLs associated with the EC2 instances do not block outbound internet traffic. Finally, make sure the network ACL associated with the NAT gateway permits the relevant traffic.

How can you validate if your VPC Subnet’s route table is correctly configured to send traffic to a VPN connection?

To validate the route table of a VPC subnet for a VPN connection, I would examine the route table entries to ensure that there is a route that points to the Virtual Private Gateway associated with the VPN connection. This route would direct specific traffic (usually identified by a particular IP range) to go through the VPN. I’d also check the VPN connection status and the VGW (Virtual Gateway) route propagation settings to ensure that the VPN and VPC are correctly linked.

If you needed to check whether the Network Load Balancer is successfully distributing traffic to multiple backend EC2 instances, what method would you employ?

To check that a Network Load Balancer (NLB) is successfully distributing traffic, I would use CloudWatch to monitor the target group and review metrics such as ‘HealthyHostCount’ and ‘UnHealthyHostCount.’ I would also verify that the NLB listener configuration matches the port and protocol used by the backend instances. Additionally, I might manually test the NLB by sending requests and checking for expected responses from different EC2 instances, assuming they are distinguishable.

When setting up a cross-region VPC peering connection, how would you test to ensure it’s configured correctly?

For a cross-region VPC peering connection, I would verify that the VPC peering status is ‘Active’ and that each VPC’s route table contains the appropriate entries to route to the peer VPC’s CIDR block through the peering connection. Also, I would ensure that there is no CIDR block overlap between the VPCs and that both sides have properly configured security groups and network ACLs to allow the required traffic. Finally, a ping or traffic test from an instance in one VPC to an instance in the other VPC would be performed to confirm connectivity.

What commands or tools can you use to simulate traffic load between application components in separate VPCs for testing purposes?

To simulate traffic load between application components in separate VPCs, one can use tools like iperf, netperf for network load testing or Apache JMeter, to simulate application-level load. AWS also provides Client VPN to securely connect to VPC resources and test internal connectivity as if they were within the network.

How can AWS Transit Gateway be tested to ensure it’s routing traffic correctly between multiple VPCs?

To test an AWS Transit Gateway’s routing capabilities, I would validate that all VPC attachments are in ‘Available’ state and confirm that the route tables within the Transit Gateway are properly configured to route traffic between the VPCs. Furthermore, I would check corresponding VPC route tables to ensure that they have routes targeting the Transit Gateway for destined traffic to other VPCs. Then I’d perform connectivity tests (like pinging EC2 instances) across VPCs to ensure traffic is flowing as expected through the Transit Gateway.