HNSEndpoint DNSServerList is ignored in 10.0.17733

[arjun024]

After running the latest Windows Insider build for 2019 (10.0.17733), we noticed that the DNSServerList for HNSEndpoint is ignored.

Steps to reproduce this error:

• Assuming we have a container and a nat network
• When we run the following program with ContainerId and NetworkName

package main

import (
	"fmt"
	"os"

	"github.com/Microsoft/hcsshim"
)

func main() {
	containerName := os.Args[1]
	networkName := os.Args[2]
	endpoint := &hcsshim.HNSEndpoint{
		VirtualNetworkName: networkName,
		Create a ComputeProcess containerName:               containerName,
	}

	endpoint.DNSServerList = "222.111.111.222,123.123.123.123"

	newEndpoint, err := endpoint.Create()
	if err != nil {
		fmt.Printf("Endpoint creation failed- %s\n", err.Error())
	}

	err = hcsshim.HotAttachEndpoint(containerName, newEndpoint.Id)
	if err != nil {
		fmt.Printf("Attaching endpoint failed\n")
	}

}

• We expect to see the (Get-DNSClientServerAddress).ServerAddresses to contain 222.111.111.222 and 123.123.123.123 in the container, but we observe that it is blank. This behavior is working as expected in 1709 and 1803 builds.

docker info:

Containers: 2
 Running: 0
 Paused: 0
 Stopped: 2
Images: 12
Server Version: master-dockerproject-2018-08-15
Storage Driver: windowsfilter
 Windows:
Logging Driver: json-file
Plugins:
 Volume: local
 Network: ics l2bridge l2tunnel nat null overlay transparent
 Log: awslogs etwlogs fluentd gelf json-file logentries splunk syslog
Swarm: inactive
Default Isolation: process
Kernel Version: 10.0 17733 (17733.1000.amd64fre.rs5_release.180803-1525)
Operating System: Windows Server Datacenter Version 1803 (OS Build 17733.1000)
OSType: windows
Architecture: x86_64
CPUs: 4
Total Memory: 32GiB
Name: WIN-8SUSKTQISJR
ID: BZ5Q:F572:PJZR:BLWE:TRIN:JWCP:FPSK:Q7ZH:UZCY:53NM:VCTY:HT5X
Docker Root Dir: C:\ProgramData\docker
Debug Mode (client): false
Debug Mode (server): false
Registry: https://index.docker.io/v1/
Labels:
Experimental: false
Insecure Registries:
 127.0.0.0/8
Live Restore Enabled: false

[pradipd]

@arjun024 Can you add the commands to create the container and network?
I've tried to repro on 17733 and couldn't repro. I tried the following:

1. docker run -d --rm -it --network none --name test windowsservercore powershell sleep 50000
2. nat.
3. docker exec test ipconfig /all
   DNS Servers . . . . . . . . . . . : 222.111.111.222
   123.123.123.123

And, I also tried creating my own nat network using:
docker network create --driver=nat n

And I get the same result as above.

Thanks.

[ankeesler]

@pradipd thank you for trying this out. We were able to reproduce the behavior that you saw above using the mcr.microsoft.com/windowsservercore-insider:10.0.17733.1000 container image.

However, this issue seems to still exist when we disable the dnscache service in a child container image. When we add this line in a Dockerfile that uses mcr.microsoft.com/windowsservercore-insider:10.0.17733.1000 as its base image, we are able to reproduce the original behavior that we reported in this github issue. We originally made this change to our container image to resolve DNS flakiness from inside the container (see #150). Per the most recent comment in that github issue, it sounds like we can keep the dnscache service on in our container image. We will try this going forward.