Any five second delay in name resolution is most likely caused by this open bug in systemd-resolved:
https://github.com/systemd/systemd/issues/11849 The root cause is a delay when resolved has to downgrade the feature set of its requests to upstream DNS servers. It correctly discovers a compatible feature set, but doesn't implement the discovered feature set until the next new query attempt. The retry logic is supposed to handle this, but the bug is that it goes crazy and retries with a known not working feature set until the max retry counter is hit. Then 5 seconds later, a new attempt is made, and works perfectly, the compatible feature set is used on the first attempt of the new query. ** Bug watch added: github.com/systemd/systemd/issues #11849 https://github.com/systemd/systemd/issues/11849 -- You received this bug notification because you are a member of Ubuntu Touch seeded packages, which is subscribed to systemd in Ubuntu. https://bugs.launchpad.net/bugs/1765477 Title: 5s delay in AAAA dns resolving; artful and earlier is quick Status in systemd package in Ubuntu: Confirmed Bug description: Basic steps: lxc launch ubuntu-daily:bionic bionic-daily lxc exec bionic-daily bash sleep 10s (because of #1765173) time host -d bionic-daily.lxd # or whatever domain your containers use by default In bionic, there is a 5s delay when requesting the AAAA record: root@wondrous-grackle:~# time host -d wondrous-grackle.lxd Trying "wondrous-grackle.lxd" ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 50934 ;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0 ;; QUESTION SECTION: ;wondrous-grackle.lxd. IN A ;; ANSWER SECTION: wondrous-grackle.lxd. 0 IN A 10.0.100.125 Received 54 bytes from 127.0.0.53#53 in 0 ms Trying "wondrous-grackle.lxd" (5s delay here) ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 17153 ;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 0 ;; QUESTION SECTION: ;wondrous-grackle.lxd. IN AAAA Received 38 bytes from 127.0.0.53#53 in 1 ms Trying "wondrous-grackle.lxd" ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 12145 ;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 0 ;; QUESTION SECTION: ;wondrous-grackle.lxd. IN MX Received 38 bytes from 127.0.0.53#53 in 0 ms real 0m5.023s In artful and xenial, there is no such delay and the (correct) empty reply is almost instantaneous. See https://pastebin.ubuntu.com/p/KP5DBcKyJr/ In both cases, /etc/resolv.conf points at 127.0.0.53 systemd version: *** 237-3ubuntu8 500 500 http://br.archive.ubuntu.com/ubuntu bionic/main amd64 Packages To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/systemd/+bug/1765477/+subscriptions -- Mailing list: https://launchpad.net/~touch-packages Post to : touch-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~touch-packages More help : https://help.launchpad.net/ListHelp
