Twelve AWS networking questions, and what the interviewer is actually listening for
I have asked some version of "walk me through why this EC2 instance can't reach the internet" in about forty interviews. Maybe six people answered it well. Not because it's hard. Because most candidates answer the question they wish had been asked. They recite what a NAT gateway is. The question was diagnostic, and diagnosis is a different skill from definition. These are the twelve that come up…
10. DNS failures within a VPC can stem from various causes, but the most common is an incorrect or missing DNS resolution configuration. If the VPC is not set up to use the private hosted zone or there's an issue with the DNS server settings, instances within the VPC may struggle to resolve domain names. Another potential cause is a misconfigured route table, where traffic intended for DNS resolution is being sent to the wrong target.
This can result in DNS requests failing to reach the appropriate DNS servers, leading to resolution errors. Understanding these nuances is crucial, as it demonstrates the candidate's ability to diagnose and troubleshoot underlying network issues effectively.
11. When designing a VPC, how do you decide on the appropriate CIDR block sizes? Selecting suitable CIDR block sizes is a critical step in VPC design, as it directly impacts address space utilization and scalability. The general recommendation is to allocate larger CIDR blocks for core components and smaller blocks for individual services or subnets.
For example, you might assign a /16 CIDR block to a VPC for broader address space and then break it down into smaller /24 or /28 blocks for different application tiers or services. This hierarchical approach allows for efficient subnetting and minimizes waste, ensuring that resources are allocated effectively while maintaining the flexibility to scale as the application grows.
12. How do you handle IP address conflicts in a multi-VPC environment? In a multi-VPC setup, IP address conflicts can arise if subnets within different VPCs contain overlapping IP ranges. To prevent such conflicts, it's essential to maintain a clear and well-documented IP address allocation plan that outlines the specific ranges assigned to each VPC.
Before provisioning resources or creating subnets, double-check that the proposed IP ranges do not overlap with those already in use. Additionally, leveraging features like VPC peering or Transit Gateway can help manage and coordinate IP address assignments across VPCs, ensuring that resources are placed in appropriate VPCs without duplicating address space.
Regularly reviewing and auditing IP address utilization can also help identify and resolve conflicts before they impact network connectivity.
Written by urgent.news from Dev.to's reporting — not their text. Machine-written — may contain errors; check the original before relying on it.
