HTML over DNS: Serving Blog Content Over DNS

Published on 17 August 2021 - development dns technology

What's up?

The past few days, I did an experiment to serve blog content over DNS (see here). That page contains mostly the same content ast this post, but it is served in a completely different manner.

This works because of DNS over HTTPS for which there is an API from Cloudflare.

Comments at Hacker News, apparently.

How it works

The DNS over HTTP API from Cloudflare is used to load the contents of that page, essentially like this:

fetch("https://cloudflare-dns.com/dns-query?ct=application/dns-json&type=TXT&name=post.hod.experiments.jacobkiers.net");

The content itself is served over DNS, using CoreDNS, with these contents:

hod.experiments.jacobkiers.net.:53 {
    log
    auto hod.experiments.jacobkiers.net. {
    directory /etc/coredns/zones/
        reload 10s
    }
}

This feeds into a zone file, which looks like this:

$TTL 5m    ; Default TTL
@    IN    SOA    experiments.jacobkiers.net.    postmaster.jacobkiers.net. (
    2021081612    ; serial
    1h        ; slave refresh interval
    15m        ; slave retry interval
    1w        ; slave copy expire time
    1h        ; NXDOMAIN cache time
    )

$ORIGIN hod.experiments.jacobkiers.net.

;
; domain name servers
;
@    IN    NS  experiments.jacobkiers.net.


;; START BLOG RECORDS
; posts-2021-08-17-serving-blog-content-over-dns-md
posts-2021-08-17-serving-blog-content-over-dns-md    60    IN    TXT    "t=text/markdown;c=3;h=2fd63f0f408ad1336283999d0487ced9;m=eyJ0aXRsZSI6IlNlcnZpbmcgYmxvZyBjb250ZW50IG92ZXIgRE5TIiwiZGF0ZSI6IjIwMjEtMDgtMTUiLCJhdXRob3IiOiJKYWNvYiBLaWVycyJ9"
0.2fd63f0f408ad1336283999d0487ced9    60    IN    TXT    "WW91IG1pZ2h0IG5vdCBiZSBhYmxlIHRvIHNlZSBpdCBpbW1lZGlhdGVseSwgYnV0IHRoZSBjb250ZW50IG9mIHRoaXMgcGFnZSBpcyB2ZXJ2ZWQgb3ZlciBETlMuCgpUaGlzIHdvcmtzIGJlY2F1c2Ugb2YgdGhlIG5ldyBETlMtb3Zlci1IVFRQIHN1cHBvcnQsIHdoaWNoLCBhdCBsZWFzdCBhdCBDbG91ZGZsYXJlLCBhbHNvIGhhcy"
1.2fd63f0f408ad1336283999d0487ced9    60    IN    TXT    "BhbiBBUEkuCgpUaGF0IEFQSSBpcyB1c2VkIHRvIGxvYWQgdGhlIGNvbnRlbnRzIG9mIHRoaXMgcGFnZSwgZXNzZW50aWFsbHkgbGlrZSB0aGlzOgoKYGBganMKZmV0Y2goImh0dHBzOi8vY2xvdWRmbGFyZS1kbnMuY29tL2Rucy1xdWVyeT9jdD1hcHBsaWNhdGlvbi9kbnMtanNvbiZ0eXBlPVRYVCZuYW1lPXBvc3QuaG9kLmV4cGVy"
2.2fd63f0f408ad1336283999d0487ced9    60    IN    TXT    "aW1lbnRzLmphY29ia2llcnMubmV0Iik7CmBgYAoKUGxlYXNlIHNlZSB0aGUgW3NvdXJjZSBjb2RlXSBmb3IgdGhlIGRldGFpbHMgb2YgaG93IGl0IHdvcmtzLgoKW3NvdXJjZSBjb2RlXTogaHR0cHM6Ly9naXRodWIuY29tL2phY29ia2llcnMvaHRtbC1vdmVyLWRucwo="

These records are base64 encoded content, so when concatenated and decoded, they give the content of the posts.

Please see the source code for the details.

FAQ

Why, though?

In short: just because I could. It was one of those ideas I was wondering idly about, and I decided to just try it.

Has it any practical use?

It is not intended to have any. Since DNS records are fairly small, serving images or something would quickly start consuming 100s of requests per second. I wouldn't want to do that to Cloudflare 😄

It would be an interesting experiment to see how feasible that is though.