getting java.net.UnknownHostException while running GOCD docker container in QNAP

Question

I am trying to run gocd docker container (https://hub.docker.com/r/gocd/gocd-server/) on QNAP (TS-451 x86 based, firmware 4.2.0) in container station.

container doesn't' start and bombs out with java.net.UnknownHostException:

May 21 20:21:28 gocd-server-1 syslog-ng[16]: syslog-ng starting up; version='3.5.3'                                                                              
using default settings from /etc/default/go-server                                                                                                               
ERROR: Failed to start Go server. Please check the logs.                                                                                                         
java.lang.RuntimeException: gocd-server-1: gocd-server-1                                                                                                         
        at com.thoughtworks.go.util.ExceptionUtils.bomb(ExceptionUtils.java:36)                                                                                  
        at com.thoughtworks.go.server.util.GoSslSocketConnector.getHostname(GoSslSocketConnector.java:102)                                                       
        at com.thoughtworks.go.server.util.GoSslSocketConnector.storeX509Certificate(GoSslSocketConnector.java:92)                                               
        at com.thoughtworks.go.server.util.GoSslSocketConnector.sslConnector(GoSslSocketConnector.java:56)                                                       
        at com.thoughtworks.go.server.util.GoSslSocketConnector.<init>(GoSslSocketConnector.java:51)                                                             
        at com.thoughtworks.go.server.Jetty9Server.sslConnector(Jetty9Server.java:133)                                                                           
        at com.thoughtworks.go.server.Jetty9Server.configure(Jetty9Server.java:76)                                                                               
        at com.thoughtworks.go.server.GoServer.configureServer(GoServer.java:84)                                                                                 
        at com.thoughtworks.go.server.GoServer.startServer(GoServer.java:70)                                                                                     
        at com.thoughtworks.go.server.GoServer.go(GoServer.java:63)                                                                                              
        at com.thoughtworks.go.server.util.GoLauncher.main(GoLauncher.java:31)                                                                                   
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)                                                                                           
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)                                                                         
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)                                                                 
        at java.lang.reflect.Method.invoke(Method.java:606)                                                                                                      
        at com.simontuffs.onejar.Boot.run(Boot.java:306)                                                                                                         
        at com.simontuffs.onejar.Boot.main(Boot.java:159)                                                                                                        
Caused by: java.net.UnknownHostException: gocd-server-1: gocd-server-1                                                                                           
        at java.net.InetAddress.getLocalHost(InetAddress.java:1496)                                                                                              
        at com.thoughtworks.go.server.util.GoSslSocketConnector.getHostname(GoSslSocketConnector.java:100)                                                       
        ... 15 more                                                                                                                                              
Caused by: java.net.UnknownHostException: gocd-server-1                                                                                                          
        at java.net.Inet4AddressImpl.lookupAllHostAddr(Native Method)

I checked /etc/hosts inside the container - it includes correct host mapping : 10.0.3.2 gocd-server-1

127.0.0.1       localhost
::1     localhost ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters
10.0.3.2 gocd-server-1

hostname resovles correctly:
root@gocd-server-1:/tmp# hostname
gocd-server-1

the container image is fine - I have run exactly the same gocd docker container on vagrant Ubuntu vm without any issues

so the issue is somehow related to QNAP Linux (which seems to be Ubuntu 4.1.2)

[~] # cat /proc/version Linux version 3.12.6 (root@NasX86-12) (gcc version 4.1.3 20070929 (prerelease) (Ubuntu 4.1.2-16ubuntu2)) #1 SMP Fri Mar 11 02:20:16 CST 2016)

any ideas how to get around java.net.UnknownHostException exception?

score 0 · Answer 1 · answered May 29 '16 at 19:32

To close this thread: though I still don't understand why this exception happens I think I found the workaround. So if you are the owner of QNAP and want to run GOCD server using ContainerStation the following steps might be useful: 1. Create a new container, using travix/gocd-server:lastest image (https://hub.docker.com/r/travix/gocd-server/). This container uses JDK8 (instead of JDK7 as official gocd container) plus it includes more options to configure (if you go to advanced settings while creating a container in ContainerStation). 2. Start the container - you will get the exception - Caused by: java.net.UnknownHostException.

Why? no idea, I am pretty sure my /etc/hosts settings are correct. In fact I know they are correct.

next step - keep the container running but ssh to your QNAP:

ssh admin@192.168.1.79 (in my case - change ip of the box to yours)

// check what images are running: docker ps -a

dde6ce028868 travix/gocd-server:latest "/docker-entrypoint.s" 21 hours ago Up 21 hours 0.0.0.0:32793->8153/tcp, 0.0.0.0:32792->8154/tcp gocd

// ssh into the container  
docker exec -it dde6ce028868 bash

// run go-server start script 
/usr/share/go-server/server.sh

let it run, in my case it successfully started gocd.

clean up work dir rm -rf /var/lib/go-server/work/
and now restart the container from ContainerStation

in my case it starts up correctly without unknown host exceptions

any theories why? (DNS caching, permissions, some initialisations which silently fail?)

score 0 · Answer 2 · edited May 23 '17 at 12:00

it turned out the issue is related to ACL which gives read access to /etc/hosts and /etc/resolv.conf only to root. So java application running inside the container under a different user, can't access these files.

pls. see this discussion for more information:.

why am I getting permission denied on file with read permissions inside Docker container?

if you want to use GOCD with QNAP - you might try to use this container https://hub.docker.com/r/rshestakov/docker-gocd-server/

which includes the following fix:

# modify ACL so go user would have read access
# to /etc/hosts and /etc/resolv.conf
# this is to avoid HostUnknown exception which happends
# when the gocd container is used on QNAP with ContainerStation
setfacl -m user:${USER_ID}:r /etc/resolv.conf
setfacl -m user:${USER_ID}:r /etc/hosts

getting java.net.UnknownHostException while running GOCD docker container in QNAP

2 Answers2