docker pull behind proxy does unnecessary dns lookup

tesharp commented 5 years ago

[x] This is a bug report
[ ] This is a feature request
[ ] I searched existing issues before opening this one

Expected behavior

When defining proxy for docker we expect it to use proxy for all commands. It should not use any longer time then normally.

Actual behavior

when pulling against private repo it takes a very long time because it first tries to resolve the dns for private repo against dns servers defined on machine. It cannot resolve the dns and uses about 1-2 minute to try resolving it before just using proxy as it should. So every pull etc takes 1-2 minute to just start.

Steps to reproduce the behavior

Create a private repo (i.e. testbug.azurecr.io) and upload image alpine.
Setup docker to use proxy
Make sure testbug.azurecr.io is not resolvable on internal dns servers
Run docker pull testbug.azurecr.io/alpine:latest, it will take a very long time to just start
Running strace -t docker pull testbug.azurecr.io/alpine:latest it should be possible to see that it tries dns lookup against internal dns servers for testbug.azurecr.io.
After a while when dns fails and it has tried all search domains it will continue anyway and pull using proxy

A hack to fix is to define testbug.azurecr.io in /etc/hosts with address 127.0.0.1. It will then manage to "resolve" the address and continue fast, still using proxy to actually pull the image. So doesn't matter what it is resolved to because it still uses proxy for pulling. Shouldn't be a need to do dns lookup at all.

WestFarmer commented 4 years ago

why this is not get any attentation ?

cpuguy83 commented 4 years ago

Why are you using a proxy instead of a mirror configuration?

Also note that your strace on "docker pull" is tracing the client, but the actual pull (including dns resolution) would happen on the daemon process.

wushuzh commented 3 years ago

In my lab env, I have set registry-mirrors in the /etc/docker/daemon.json, but pull fail with dns query and cannot continue pull image from registry mirror.

# docker pull bitnami/metallb-controller
Using default tag: latest
Error response from daemon: Get https://registry-1.docker.io/v2/: dial tcp: lookup registry-1.docker.io on [::1]:53: read udp [::1]:41737->[::1]:53: read: connection refused

# cat /etc/docker/daemon.json
{
  "registry-mirrors": ["https://mirror.myinternal.repo"]
}

docker / for-linux