Understanding TTL (time-to-live)
Time to live is what dictates how long it will be until your computer refreshes its DNS related information. For example, the IP address your domain name points to or where your MX records are directing email.
This time is defined in seconds and the default setting can be found in the zone file (available in the AccountCenter under Edit Zone File). The reason this is useful is that if you will be moving hosts, or if you have any sort of DNS information that you need to change, it will take affect in a shorter time interval.
Generally, DNS propagation takes 24 to 48 hours to complete whenever any changes are made to the Zone File. Lowering the TTL prior to making the change will reduce the time for propagation.
Let's say you want to change your email from your (mt) Media Temple account to Google Apps. If you make this change now, with the default TTL of 43,200 seconds (12 hours), it will be up to 12 hours until all the email is directed at Google.
However, in the meantime, email will still be coming to either your (mt) Media Temple account or to Google (depending on when the last time that server checked your MX records). It's not a very elegant solution to have to tell your employees, clients, what have you, to check two email accounts for that duration.
Instead, let's make that change happen in five minutes.
How, you ask?
Easy! In the AccountCenter, you can lower the TTL down to a five minute value. All it takes to make this transition smooth is a 12-hour preparation time:
- First, go ahead and login as normal.
- Now, you'll want to choose the domain that you want to lower the TTL for from the "Domains" tab.
- On the bottom left, you'll see an option that reads Edit Zone File, go ahead and click that.
- This is where the magic happens. You'll see a button that reads Lower TTL, push that button!
- Wait 12 hours before you proceed to...
- ... make your DNS changes!
After you push that button, and future DNS requests are going to see the TTL as five minutes and by that rule, they will only store that information for that five minute period. If five minutes go by and your computer needs that information again, it won't check its cache. Instead, it will retrieve fresh, brand new, information.
This is why we need to wait the 12-hour period. Some computers still have that 12-hour period saved, and they'll continue to retain that information until that precise time has elapsed. Once that time has elapsed, if they check again and you've lowered the TTL, they will only preserve those details for a mere 5 minutes.
Explanation and Benefits
This 12-hour period is what makes sure that everyone is on the same page. Once it has elapsed, any DNS related changes you make will occur and be visible within only 5 minutes!
What does that mean to you?
Here is a (very) brief list of why this is useful:
- For the email situation above, that means that only a brief 5 minute window exists where email may be sent to the wrong place. This is minimal in comparison to our early 12-hour time frame.
- Made a DNS change and something's just not quite working? Don't fret! Five minutes is all you need to revert the changes and have them take affect so you can continue to work.
Of course, after your changes have been made, you can proceed to Raise the TTL to make life a little easier on (mt) nameservers. But no worries -- if you forget, (mt) will automatically increase it for you after a few days.