Comment by tzs
7 years ago
> Of course, a service can switch to a new cloud provider, a new server, a new network, requiring clients to use up-to-date DNS records. And having reasonably low TTLs helps make the transition friction-free. However, no one moving to a new infrastructure is going to expect clients to use the new DNS records within 1 minute, 5 minutes or 15 minutes. Setting a minimum TTL of 40 minutes instead of 5 minutes is not going to prevent users from accessing the service.
Note that you can still get the benefit of a low TTL during a planned switch to a new cloud provider, server, or network even if you run with a high TTL normally. You just have to lower it as you approach the switch.
For example, let's say you normally run with a TTL of 24 hours. 25 hours before you are going to throw the switch on the provider change, change the TTL to 1 hour. 61 minutes before the switch, change TTL to 1 minute.
Wouldn't you be canarying your switch over a period of longer than 24 hours anyway?
I can still imagine a benefit to short TTLs in the sense that you can maybe roll out your canary in a more controlled way. But that's a lot more complicated than the issue of quick switching.
If it's planned, yes.
If your cloud provider does an oopsie (e.g. https://news.ycombinator.com/item?id=20064169) and takes down your entire infrastructure, or you have to move quickly for some other reason, or you're recovering from a misconfiguration, the long TTL can add 24 hours to your mitigation time.
If you're just playing around with your personal project/web site, you just added a giant round of whack-a-cache to your "let's finally clean up my personal server mess" evening.
As most who's ever worked with web hosting can confirm, small business customers often have no idea of what they're doing, and I've talked to many people who switched providers after seeing an ad for cheap hosting, without realising that they have to a) wait for the DNS changes to propagate, b) that they have to actually move their web site from one provider to another.
Subsequently, my previous employer lowered the default TTL simply because it got rid of all the bad Trustpilot ratings about customers being "prevented from leaving", and started offering a "move my WordPress site for me" service to profit from all the panicking new-comers who had no idea about how to do trivial things like importing/exporting a database and transferring files.