Docker: Jenkins container can't access internet on QNAP device - jenkins

Question

I try to get the Docker image (1.651.3 or latest version) running on my QNAP NAS using the internal ContainerStation.
Just using the default settings without setting any parameters or binding any resource, I can't access the internet. I already tried the NAT or Host network mode, but this would make no difference.
Stacktrace:
Oct 02, 2016 1:55:07 PM javax.jmdns.impl.HostInfo newHostInfo
WARNING: Could not intialize the host network interface on nullbecause of an error: 5929616b9f0b: 5929616b9f0b: unknown error
java.net.UnknownHostException: 5929616b9f0b: 5929616b9f0b: unknown error
at java.net.InetAddress.getLocalHost(InetAddress.java:1505)
at javax.jmdns.impl.HostInfo.newHostInfo(HostInfo.java:75)
at javax.jmdns.impl.JmDNSImpl.<init>(JmDNSImpl.java:407)
at javax.jmdns.JmDNS.create(JmDNS.java:60)
at hudson.DNSMultiCast$1.call(DNSMultiCast.java:32)
at jenkins.util.ContextResettingExecutorService$2.call(ContextResettingExecutorService.java:46)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:745)
Caused by: java.net.UnknownHostException: 5929616b9f0b: unknown error
at java.net.Inet4AddressImpl.lookupAllHostAddr(Native Method)
at java.net.InetAddress$2.lookupAllHostAddr(InetAddress.java:928)
at java.net.InetAddress.getAddressesFromNameService(InetAddress.java:1323)
at java.net.InetAddress.getLocalHost(InetAddress.java:1500)
... 9 more
Using bash:
$ ping google.de
ping: unknown host
Any idea what might be the problem? Any other docker image can access the internet, only this image has these problems.

Answer 1

I recently experienced the same problem and in my case it turned out to be caused by the ACL lists on the QNAP, preventing the jenkins user in the container from reading the /etc/hosts and /etc/resolv.conf files.
Here's how I fixed it. Perhaps it can be of some help to you as well:
ssh to the QNAP
$ ssh admin#<your IP or domain name here>
Manually create a jenkins user on the QNAP with UID 1000 (the same
UID as the jenkins user in the container)
$ useradd -u 1000 -M -s /bin/false jenkins
Log into the QNAP web interface
Navigate to Control panel -> Users
Click the Edit Shared Folder Permissions icon for the jenkins user
Tick the RW checkbox (Read/Write access) for the Container folder
and click Apply
Start your Jenkins container
Disclaimer: I am no sysadmin so I don't know whether this approach would cause any security issues on your system. You may want to look into that before giving outside access to your Jenkins web interface... :)