while upgrading my stacks from Rancher 1.6 to 2.1 I ran into a strange issue.
I deployed nextcloud:13-fpm-alpine as workload + a sidecar for the cronjob and all the other services needed (Redis, MariaDB, …) and everything was looking good.
However, external DNS is broken inside of the Nextcloud container only. The Redis and MariaDB container resolve rancher.com just fine but the Nextcloud container and sidecar will fail to resolve anything that isn’t a discoverable service.
The output inside of the Nextcloud container looks like this:
/var/www/html # nslookup rancher.com nslookup: can't resolve '(null)': Name does not resolve nslookup: can't resolve 'rancher.com': Try again
options ndots:5 from resolv.conf will lead to a result but it takes 5-10 seconds:
/var/www/html # nslookup rancher.com nslookup: can't resolve '(null)': Name does not resolve Name: rancher.com Address 1: 126.96.36.199 Address 2: 188.8.131.52 Address 3: 2606:4700:20::6818:1033 Address 4: 2606:4700:20::6818:1133
This is the only workload where this happens, with the difference being that it has a sidecar and it uses the Nextcloud image. This works fine in both Rancher 1.6 and any other workload in this project/namespace.
Any ideas what could cause this? Does anybody else see this with the image nextcloud:13-fpm-alpine?