DevOps, SRE & Cloud Interview · Networking, Security & LLMOps · Lesson 1 of 3
DNS, load balancing & TLS
A handful of networking primitives sit under every deployed system, and interviewers probe whether you understand them end to end.
DNS
- DNS resolves a name (api.example.com) to an IP via a hierarchy (root → TLD → authoritative). Results are cached per the TTL.
- Common records: A/AAAA (name → IP), CNAME (alias), MX (mail). Low TTLs enable faster failover but more lookups.
Load balancing & TLS
- L4 (transport) load balancers route by IP/port; L7 (application) route by HTTP host/path and can do TLS termination, sticky sessions, and canary routing.
- TLS gives encryption + server identity via a certificate. The handshake authenticates the server (chain of trust to a CA) and negotiates a symmetric session key.
- TLS termination at the load balancer offloads crypto from app servers; re-encrypt inside the mesh if you need end-to-end.
DNS is the phone bookDNS is the internet's phone book: you know the name, it returns the number (IP). The TTL is how long you may keep that entry before looking it up again — short TTL means faster changes, more lookups.
◆ Lock it in
- DNS resolves names to IPs through a cached hierarchy; TTL trades freshness for lookup volume.
- L4 load balancers route by IP/port, L7 by HTTP and can terminate TLS and do canary routing.
- TLS = encryption + server identity via a CA chain; terminate at the LB, re-encrypt internally if needed.
Feynman drill — say it out loudTrace what happens from typing a URL to a TLS-encrypted response: DNS, load balancer, TLS handshake.
Step 1 rate your confidence · Step 2 pick your answer
What does an L7 (application) load balancer do that an L4 one cannot?
Step 1 — how sure are you?