New blog post: Stop using ridiculously low DNS TTLs, now https://00f.net/2019/11/03/stop-using-low-dns-ttls/ …
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Replying to @jedisct1
You can’t just lob “The urban legend that DNS-based load balancing depends on TTLs (it doesn’t)“ without an explanation! If I have an endpoint go away I want people to stop using it quickly. (Or are you referring to the case where all the endpoints are up?)
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DNS-based load balancing relies on multi-value DNS records. If an endpoint fails the client can try the next value in the record without having to do another query. As long as the clients are quick at doing this, having dead endpoints in the record is not much of a problem.
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It increases the time before a replacement can receive traffic though.
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The myth being debunked is that DNS-based load balancing relies on TTLs to spread traffic across multiple backends. It doesn't: it uses multi-value DNS records for that. DNS TTL is required to update the backend list, but long TTLs don't stop the load balancing from working
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Replying to @boomerangfish @Miller_Geek and
Does the order of addresses returned by the DNS server matter? Or is the client supposed to choose randomly?
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It doesn’t matter at all. If you want a skewed distribution, an address can be present multiple times.
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