Recently, I changed my domain to point to a new server but faced a frustrating delay. After updating the A record and waiting, my old website kept showing up despite clearing my browser cache and restarting my computer. It wasn't until three hours later that I learned about TTL (Time To Live). My previous A record had a TTL of 3600 seconds (1 hour), meaning that resolvers cached the old IP for that duration. This experience led me down a rabbit hole exploring various aspects of DNS, including the hierarchy (Root → TLD → Domain), different record types (A, AAAA, CNAME, MX, TXT), the propagation trade-off with TTL, the resolution process occurring upon URL entry, and distinguishing between resolvers and nameservers. I also discovered useful commands to view and clear DNS caches. A key lesson I picked up: if you're planning a server migration, it's wise to lower your TTL to 300 a few days in advance to help old cached records expire much faster. I'm curious, what's something you use daily that you only really understood when something went wrong?
2 Answers
This is a really nice breakdown! One thing you might add is that every hostname technically has an implied period at the end (like www.example.com.), marking it as a complete domain at the root. I was pretty surprised when I stumbled across that fact. Also, just a head's up, some of your content isn't visible in the UK.
Great write-up! The TTL thing is definitely a common "why didn’t someone tell me this before?" situation, haha. I've also noticed that different DNS providers handle propagation in their own ways. For example, Cloudflare might update immediately, but Google's 8.8.8.8 might show the old IP for an extra 20 minutes. It can feel so random troubleshooting until you check a few different resolvers. Also, some ISPs completely ignore TTL settings and cache things for longer than they should, which is super frustrating during migrations. I always drop my TTL to 300 about 48 hours ahead now to avoid issues. What actually broke that led you to learn all this? Was it just curiosity or did something go haywire?
Thanks for the input! Great point about the trailing dot; I should include that. About the UK visibility issue, is it just certain images or the entire article? My images are on Imgur, which sometimes faces restrictions on different networks.