IIRC it spiders from a static list of a handful of servers by asking their peers.
If you're familiar with PHP, you can read the source here https://git.sumptuouscapital.com/?p=sks-keyservers-pool.git;a=blob;f=sks-keyservers.net/status-srv/sks.inc.php On 2020-08-02T07:41:05+0200 Kiss Gabor (Bitman) <ki...@ssg.ki.iif.hu> wrote 0.3K bytes: > Dear Kristian, > > How does sks-keyservers.net work? > More precisely how could a server get off the list? > > E.g. fks.pgpkeys.eu is unreachable since 14 months, no other > servers refer it but it does not disappear from the list. > > keys01.fedoraproject.org and keys02.fedoraproject.org are also > unreferenced and seem to work never. > > Cheers > > Gabor >
