Traccar process not binding to IPv6 stack

[Kaldek]

Running the latest Docker image here, and while the container will happily take an IPv6 address, the Traccar service doesn't bind to the IPv6 stack.

/opt/traccar # ifconfig
eth0      Link encap:Ethernet  HWaddr 00:xx:xx:xx:xx:71  
          inet addr:192.168.0.217  Bcast:192.168.0.255  Mask:255.255.255.0
          inet6 addr: 2404:xxxx:xxxx::d00d:d00d/64 Scope:Global
          inet6 addr: fe80::1b:2100:xxxx:xxxx/64 Scope:Link
          inet6 addr: 2404:xxxx:xxxx:xxxx:xxxx:xxxx:xxxx:xxxx/64 Scope:Global
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:1077 errors:0 dropped:0 overruns:0 frame:0
          TX packets:326 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:244656 (238.9 KiB)  TX bytes:74289 (72.5 KiB)

/opt/traccar # netstat -an
Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address           Foreign Address         State       
tcp        0      0 127.0.0.11:37749        0.0.0.0:*               LISTEN      
tcp        0      0 0.0.0.0:5019            0.0.0.0:*               LISTEN      
tcp        0      0 0.0.0.0:5018            0.0.0.0:*               LISTEN      

...SNIP...

tcp        0      0 192.168.0.217:8082      192.168.0.210:39680     TIME_WAIT   
tcp        0      0 192.168.0.217:8082      192.168.0.210:39718     ESTABLISHED 
tcp        0      0 192.168.0.217:8082      192.168.0.177:37100     ESTABLISHED 
udp        0      0 127.0.0.11:48705        0.0.0.0:*                           
udp        0      0 0.0.0.0:5001            0.0.0.0:*                           
udp        0      0 0.0.0.0:5002            0.0.0.0:*                           
udp        0      0 0.0.0.0:5003            0.0.0.0:*                           
udp        0      0 0.0.0.0:5004            0.0.0.0:*                           
udp        0      0 0.0.0.0:5005            0.0.0.0:*                           
udp        0      0 0.0.0.0:5008            0.0.0.0:*                           
udp        0      0 0.0.0.0:5009            0.0.0.0:*                           
udp        0      0 0.0.0.0:5013            0.0.0.0:*                           

... SNIP...

udp        0      0 0.0.0.0:5254            0.0.0.0:*                           
Active UNIX domain sockets (servers and established)
Proto RefCnt Flags       Type       State         I-Node Path
unix  2      [ ]         STREAM     CONNECTED     41382888

/opt/traccar # ps
PID   USER     TIME  COMMAND
    1 root      1:18 java -Xms1g -Xmx1g -Djava.net.preferIPv4Stack=true -jar tracker-server.jar conf/traccar.xml

Not sure if the Java execution command is the problem here as it says "preferred".

[Kaldek]

Alright this does look to be the problem (lots of Googling here; I'm not a Java guy). This "preferred" setting stops the use of IPv6.

[tananaev]

@magna-z do you know why we need java.net.preferIPv4Stack=true?

[malantp]

Is there any way for the traccar service to use IPv6 in a docker environment? This would be great to avoid NAT.

[tananaev]

@magna-z

[magna-z]

IPV6 is rarely used, especially in conjunction with Docker, as there are many related difficulties in configuration, debugging, and it is easy to make mistakes in configuring the firewall. If it is needed and will be used consciously, you can enable it by running the container --entrypoint="java -Xms1g -Xmx1g".

[tananaev]

But why do we need to force IPv4? Shouldn't it use the right thing by default?

[magna-z]

Previously, I often encountered problems using IPv6 along with Docker. But since there is a request for basic IPv6 support, it means that the problems are no longer relevant and you can remove java.net.preferIPv4Stack=true from the default ENTRYPOINT and make changes in the next release.

At the same time, we can discuss the basic values of -Xms1g and `-Xmx1g'.

[tananaev]

Typically those are also not needed, but what do you think?