Hacker News Reader

Comment by meetups323 | Hacker News Reader

> When people say “we’re waiting for DNS to propagate”, what they actually mean is “we’re waiting for cached records to expire”.

And when people say "the new data needs to propagate" they usually mean "all the old versions of the data need to be replaced with the updated version". Which is exactly the what "waiting for cached records to expire" means. I don't really see the point of this article, besides to express some sort of overly pedantic characterization of push vs pull event propagation techniques. Did anyone really think that every time someone makes a DNS update it is broadcasted to every DNS resolver on the internet?

Edit in response to general feedback: The article should be titled "DNS doesn't push". The DNS consistency process satisfies any reasonable definition of "propagation" so claiming "DNS doesn't propagate" is confusing at best and misleading clickbait at worst.

View on HN

> Did anyone really think that every time someone makes a DNS update it is broadcasted to every DNS resolver on the internet?

Absolutely. All of these, especially to an average person, imply the data takes a while to be pushed out "across the internet".

GoDaddy [1]: "but it can take up to 48 hours for everything to propagate across the Internet"

Namecheap [2]: "it is a period of time ISP (Internet service provider) nodes across the world take to update their caches with the new DNS information of your domain."

AWS [3]: "DNS propagation is the amount of time that it takes for DNS changes to be updated across the internet"

[1] https://www.godaddy.com/help/what-factors-affect-dns-propaga...

[2] https://www.namecheap.com/support/knowledgebase/article.aspx...

[3] https://aws.amazon.com/premiumsupport/knowledge-center/route...

Which, again, just translates to "but it can take up to 48 hours for other nameservers to have caught up".

Those are both true statements. They also don't imply a push model.

I don't really see the point of your comment, besides to express some sort of overly pedantic characterization of push vs pull event propagation techniques.

You're the one making the distinction.

Am I? I don’t have a horse in this race.

I responded because I felt the “Did anyone really think” comment was arrogant and dismissive. I provided examples where a layperson could easily reach that conclusion.

Yes. It’s the effect that propagates.

They do imply a push. A pull would mean that things mightn't spread across the internet in the event no-one requested them. Those statements do imply that things just get spread across the internet automatically.

Can news propagate?

If someone claimed that in 48 hours everyone on the planet would've heard some news, that would imply a push, yes.

"By 48 hours, the news will have spread around the globe." (a more natural phrasing than propagate in the context of news, but I think pretty identical in implication) does not imply a push model, I just completely disagree with you.

It doesn't matter how pedantic the correction seems from the perspective of those of us who understand DNS, because we aren't the target audience of the correction. Tightening up the terminology is a small price to pay for being helpful.

> Did anyone really think that every time someone makes a DNS update it is broadcasted to every DNS resolver on the internet?

Yes. Absolutely. Well, not every DNS resolver on the internet, but at least every one that has it cached.

I think it's partly because push-propagation does happen at very limited parts of the picture, when updating master replicas.

It's not pedantic, because there is an observable, human-significant behavioral difference: if you update a DNS record and then test it before the TTL has expired, there's a good chance you'll already see the update. And a good chance that then testing immediately from somewhere else, you won't see the update.

With the mental push model of DNS propagation, you have to reach for weird explanations for this behavior -- "oh, I guess something is still working through its list of servers to push this to" or something equally dubious. With the stale cache entry mental model, it's just: "it wasn't in the cache".

I have heard dozens of people describe DNS this way, yes, like it's a push behaviour. I don't know how much it matters but I think making it clearer is good.

Then the article should be titled "DNS doesn't push". Claiming it doesn't propagate is bizarre.

DNS servers push to other authoritative resolvers. There are all kinds of topologies for zone transfers.

It's not what a user thinks of, but in terms of I updated a record and have to wait for it to be "everywhere" it's entirely part of the change latency to the end user and outside the scope of caching and TTLs being honored.

Propagation fairly strongly implies something emanating from a source.

If I write a book and publish it, am I not propagating the ideas written on it? I still require readers to go online or to a bookshop and purchase my book, then read it. Once they do, the information has propagated to them. If someone explicitly asks them about the book and gets a good explanation, my ideas propagate further.

In the case of DNS, the information does emanate from the upstream server, but only upon request, like the ideas in the book.

> am I not propagating the ideas written on it

I don't think anyone would phrase it that way, no. "Propaganda" generally involves things like mass leaflet drops, messages blasted out of public address systems, that sort of thing.

Who said anything about propaganda? Not all ideas are classified that way, and I was talking about writing a book, not dropping leaflets.

Indeed. But the reason propaganda is called such is because it's an information push - to propagate (same root word) rather than publish information.

If you monitor the TTL changes in DNS records, you can spot when the best admins are going to be doing some major updates because the TTL decreases.

> Did anyone really think that every time someone makes a DNS update it is broadcasted to every DNS resolver on the internet?

This behavior might indeed apply to many services with a global DNS footprint (multi-continent redundant authoritative DNS servers), but that's even more pedantic and, in the end, we just want the DNS update be realized by all users in a respectable amount of time.

Andy Rooney made a career out of nitpicking commonly accepted declarative english statements and commonalities in the language.

> misleading clickbait at worst

I mean, considering what the source is (jvns.ca is a blog that is fairly well known around these parts to talk about technical content), and the usage of quotes in the title, one should hopefully infer that there's going to be some level of pedantry in this post.

I share the sentiment that for the average joe, a push vs pull distinction is fairly irrelevant, and that for the more networking-savvy, this is all more or less old news. This feels like the type of post that is targeted at the 10,000[0] people in between who may not realize that their mental model of DNS propagation may not be correct (and they'd appreciate being nudged about it)

[0] https://xkcd.com/1053/

Your personal semantic disagreement (which per responses is clearly not the only way to see things) does not make an article clickbait.

Reply on news.ycombinator.com