How Low Should I Set TTL for DNS Zones?

There really isn't a one-size-fits-all answer here. It all depends on how frequently you anticipate making changes. If you know there are upcoming changes, lowering the TTL in advance can help minimize downtime during switchover, letting you cut over quickly. But remember, if you set it too low for too long, in case of a major DNS outage, your records could expire from caches and cause problems. It's a balancing act.

I usually drop the TTL to a minute when I know a change is coming, then bring it back up to an hour after everything is settled. This way you get the benefits of fast propagation and still keep your DNS server from being overloaded. The default 24-hour TTL is there for a reason, but it works fine for normal operations.

Watch out for major DNS servers; they often ignore your TTL settings if they're too low, just to prevent potential DDoS attacks. Doing so can lead to unexpected propagation behavior. For things like SPF/DKIM records for email, it's best to keep the TTL longer—ideally over an hour. But if you're just dealing with web traffic, a 1-hour default is usually good enough.

I think lowering the TTL to something like 5 minutes might work well for quick changes. Just keep in mind that a lower TTL can lead to more frequent queries to your authoritative DNS server, which could increase latency and the load on your DNS server. However, you probably won't notice a significant impact with a lower TTL unless you're handling a massive amount of traffic.