hi all. OP here. iāve been doing some further investigation and iāve found the source of the 20 second delay. ironically it was, as I initially suspected, a DNS lookup.
by performing a tcpdump on the docker0 interface using the original (first) collabora docker image I could see a whole pile of DNS lookup requests directed to 192.168.65.1. this isnāt an IP that has anything to do with my infrastructure or anything to do with my docker setup.
when I updated to the most recent collabora docker image, this has now changed to direct to 192.168.100.1. again, not an IP address thatās related to me.
09:35:30.230560 IP 172.17.0.1.59310 > 192.168.100.1.53: 57049+ A? fca10b4e59a4.site. (35)
09:35:35.235168 IP 172.17.0.1.59310 > 192.168.100.1.53: 57049+ A? fca10b4e59a4.site. (35)
when I first saw this I jumped into the collabora image and searched for references to 192.168.65.1. I repeated this for the current docker image and found this:
/opt/lool/systemplate/etc/resolv.conf:
# Generated by NetworkManager
search site
nameserver 192.168.100.1
i tried to change this, but the edit didnāt seem to apply. iām suspecting this file is automatically generated when the docker image launches.
at the moment iām trying to see if there is anything in docker i can reconfigure to accommodate for this. i know that in docker 1.10 and above there is a DNS proxy feature and I wonder if there is somehow I can setup docker to receive the DNS requests and proxy them across.
iām still not sure where the 192.168.100.1 IP address is generated from, and I also donāt know why this IP changed from the first image 192.168.65.1. interestingly enough if I google for docker and either of these two IP addresses I find quite a few users with similar setups. i havenāt built anything in docker and I donāt know if any of this originates from an introductory guide or similar.
if the person who is responsible for creating this docker image is available to comment and perhaps provide any information about how the docker daemon is launched on their system with any specific networking options this might greatly assist. it would also be of great interest if either of the two above IP addresses mean anything to the original builders infrastructure.
iāll post up more information if I discover anything that I can change in docker land that changes this functionality.
cheers, wizdude.