Very cool. Is this only commercial aircraft? Would be interesting to see if general aviation VFR craft also decreased even though they were technically still allowed to fly as long as it wasn’t from ATC controlled air strips. Though you wouldn’t be able to show it relative to the “expected” number of flights since they aren’t on scheduled flight routes.
I remember seeing a similar cool GIF for 9/11 flights, and thought it'd be cool to see if for today's ground stop too, and had Claude Code generate the website in ~30 mins.
Liked it so much and thought I'd clean it up a bit, deploy, and share :) Enjoy!
Fun irony (beyond being Friday the 13th): FAA lost radar and frequencies between centers but ADS-B is broadcast by the planes themselves, so a couple hundred hobbyist receivers probably kept the full picture the whole time.
contrary to popular belief, DNS doesn't actually need 24 hours (or whatever) to "propagate". It only needs enough time for caches to expire, if they exist. For non-existent domains this shouldn't be an issue.
DNS controls the length of time an answer is valid (with time-to-live/TTL), some (poorly configured, but for a historical good reason) caching servers ignore the TTL and keep the record much longer (~24 hours).
A non-existent (not yet resolvable) domain, will get an NXDOMAIN response which also gets cached via a TTL setting (which again might be ignored by caching servers).
All that caching - while the current response is still "valid" because the TTL hasn't expired - is what people call "propagation".
Aside from regular caches (that use TTLs), there can also be a replication delay between primary master and secondary master servers.
You make your changes to the zone file on the primary server. The secondary replicates the zone file (a "zone transfer") and uses its copy to serve requests, enabling you to have multiple authoritative servers.
In the old days, the secondary server simply polled the primary server at a fixed interval to see if its zone data was out of date. It could potentially be hours if that's the schedule you chose. It wasn't uncommon to restart the secondary servers by hand if you needed something to propagate faster.
Later, more sophisticated stuff was added like incremental zone transfers and the ability for the primary to send a notification to the secondary instead of relying only on polling. Those made it more practical to replicate quickly.
There were scenarios back in the day when quick replication wasn't worth the cost. The primary and secondary servers might be on opposite sides of a 9600 baud modem connection where zone transfers would eat up a significant portion of available bandwidth.
TLDR: DNS "propagation" is real, not a myth. It's just that today it's pretty trivial to make the propagation delay so tiny that it's negligible.
Very cool. Is this only commercial aircraft? Would be interesting to see if general aviation VFR craft also decreased even though they were technically still allowed to fly as long as it wasn’t from ATC controlled air strips. Though you wouldn’t be able to show it relative to the “expected” number of flights since they aren’t on scheduled flight routes.
I remember seeing a similar cool GIF for 9/11 flights, and thought it'd be cool to see if for today's ground stop too, and had Claude Code generate the website in ~30 mins.
Liked it so much and thought I'd clean it up a bit, deploy, and share :) Enjoy!
Everyone I shared this with while stuck in transit today loved it. Thanks for inspiring some good vibes in Montreal!
I had the same idea (https://germon.me/experiments/ground-stop/), this is awesome, great stuff
Something about planes and data visualisation I love, been focus of so many of my random side projects
Really fast work! I didn't know all of this data was publicly available.
Fun irony (beyond being Friday the 13th): FAA lost radar and frequencies between centers but ADS-B is broadcast by the planes themselves, so a couple hundred hobbyist receivers probably kept the full picture the whole time.
Wow, impressive TTM. Barely enough time for the domain to resolve!
>Barely enough time for the domain to resolve!
contrary to popular belief, DNS doesn't actually need 24 hours (or whatever) to "propagate". It only needs enough time for caches to expire, if they exist. For non-existent domains this shouldn't be an issue.
DNS controls the length of time an answer is valid (with time-to-live/TTL), some (poorly configured, but for a historical good reason) caching servers ignore the TTL and keep the record much longer (~24 hours).
A non-existent (not yet resolvable) domain, will get an NXDOMAIN response which also gets cached via a TTL setting (which again might be ignored by caching servers).
All that caching - while the current response is still "valid" because the TTL hasn't expired - is what people call "propagation".
Aside from regular caches (that use TTLs), there can also be a replication delay between primary master and secondary master servers.
You make your changes to the zone file on the primary server. The secondary replicates the zone file (a "zone transfer") and uses its copy to serve requests, enabling you to have multiple authoritative servers.
In the old days, the secondary server simply polled the primary server at a fixed interval to see if its zone data was out of date. It could potentially be hours if that's the schedule you chose. It wasn't uncommon to restart the secondary servers by hand if you needed something to propagate faster.
Later, more sophisticated stuff was added like incremental zone transfers and the ability for the primary to send a notification to the secondary instead of relying only on polling. Those made it more practical to replicate quickly.
There were scenarios back in the day when quick replication wasn't worth the cost. The primary and secondary servers might be on opposite sides of a 9600 baud modem connection where zone transfers would eat up a significant portion of available bandwidth.
TLDR: DNS "propagation" is real, not a myth. It's just that today it's pretty trivial to make the propagation delay so tiny that it's negligible.
What’s underlying data source for it all?
Flight positions: adsb.fi community ADS-B network. Airport delay feed: FAA NAS Status
Related:
FAA issues national ground stop
https://news.ycombinator.com/item?id=50489641
FAA lifted National Ground Stop at 0119Z
https://news.ycombinator.com/item?id=50492601