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What do you recommend then? DNS doesn't usually change that often, but if you mess it up when it does, you're in for some pain if TTLs are high!
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Not the one you're replying to, but I'd keep TTL high normally and lower it one TTL ahead of a planned change.
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I would define high as "double time needed to fix a dns issue" and account for weekends
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This is the way.
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Unfortunately you can't set DNS TTL arbitrarily high (or low) without some resolvers ignoring your suggestion and using arbitrary values.
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Most historical outages lasted minutes or hours. One arguably lasted much longer, when someone lost control of their servers due to civil war.

I haven't followed this closely, but have there been any... shall we say plain outages longer than six hours? That's not an outrageous TTL. Or a day.

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This assumes that the host name you want has been recently queried. If it's not cached, good luck...
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