java.net.SocketException when accessing docker hos

I'm new to docker and need to connect from inside a running centos docker container to the host running the container using a java socket. When trying to connect a SocketException occurs:

[root@743fedf46128 test]# java SocketTest 10.1.196.134 4444 127.0.0.1 0
Trying to connect using ip address
Using remote ip 10.1.196.134
Using remote port 4444
Using local ip 127.0.0.1
Using local port 0
/10.1.196.134, 4444, /127.0.0.1, 0
    java.net.SocketException: Invalid argument or cannot assign requested address
    at java.net.PlainSocketImpl.socketConnect(Native Method)
    at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:339)
    at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:200)
    at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:182)
    at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392)
    at java.net.Socket.connect(Socket.java:579)
    at java.net.Socket.connect(Socket.java:528)
    at SocketTest.main(SocketTest.java:54)

The Java Class TestSocket actually only tries to open a socket:

    public static void main(String[] args) {
    String remoteIp = args[0];
    String remotePort = args[1];
    String localIp = args[2];
    String localPort = args[3];


    System.out.println("Trying to connect using ip address");
    System.out.println("Using remote ip " + remoteIp);
    System.out.println("Using remote port " + remotePort);
    System.out.println("Using local ip " + localIp);
    System.out.println("Using local port " + localPort);

    Socket workSocket = null;
    try {
        InetAddress remoteAddress = InetAddress.getByName(remoteIp);
        InetAddress localAddress = InetAddress.getByName(localIp);
        int rPort = Integer.parseInt(remotePort);
        int lPort = Integer.parseInt(localPort);
        System.out.println(remoteAddress + ", " + rPort + ", " + localAddress + ", " + lPort);
        workSocket = new Socket();
        workSocket.setReuseAddress(true);
        workSocket.bind(new InetSocketAddress(localAddress, lPort));
        workSocket.setSoTimeout(1000);
        workSocket.connect(new InetSocketAddress(remoteAddress, rPort));
    }

And it fails on the last line (the connect).

Ping as well as telneting the port from within the running container however work:

[admin@pluto ~]$ docker exec -it --user root pensive_almeida bash
[root@743fedf46128 test]# ping -c 3 10.1.196.134
PING 10.1.196.134 (10.1.196.134) 56(84) bytes of data.
64 bytes from 10.1.196.134: icmp_seq=1 ttl=64 time=0.047 ms
64 bytes from 10.1.196.134: icmp_seq=2 ttl=64 time=0.101 ms
64 bytes from 10.1.196.134: icmp_seq=3 ttl=64 time=0.099 ms

--- 10.1.196.134 ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 1999ms
rtt min/avg/max/mdev = 0.047/0.082/0.101/0.026 ms

[root@743fedf46128 test]# telnet 10.1.196.134 4444
Trying 10.1.196.134...
Connected to 10.1.196.134.
Escape character is '^]'.
This is a test
Connection closed by foreign host.

Can anybody provide me a hint, why trying to connect fails with java ? For completness, my Dockerfile looks like this:

FROM centos:centos7

# Set the proxies
ENV HTTP_PROXY 'http://175.23.236.88:3128/'
ENV HTTPS_PROXY 'http://175.23.236.88:3128/'

# Install telnet
RUN yum -y install telnet
RUN yum -y install wget

# Prepare environment
ENV JAVA_HOME /opt/java
ENV PATH $PATH:$JAVA_HOME/bin

# Install Oracle Java7
RUN wget --no-check-certificate --no-cookies --header "Cookie:oraclelicense=accept-securebackup-cookie" \
        http://download.oracle.com/otn-pub/java/jdk/7u80-b15/jdk-7u80-linux-x64.tar.gz && \
        tar -xvf jdk-7u80-linux-x64.tar.gz && \
        rm jdk*.tar.gz && \
        mv jdk* ${JAVA_HOME}

WORKDIR /opt/test

# Add the test class
ADD dockerfiles/SocketTest.class /opt/test/SocketTest.class

Thank you in advance for your replies.

回答1:

You could add --net=host to your docker run command, but in that way the host has full access to your container. You can however expose a port within your Dockerfile or on the outside in your docker run command, but I prefer the former.

Here's an example of mine:



Pull base image

FROM ubuntu:14.04

RUN apt-get update
RUN apt-get install software-properties-common -y
RUN add-apt-repository ppa:webupd8team/java -y
RUN apt-get update
RUN echo debconf shared/accepted-oracle-license-v1-1 select true | debconf-set-selections
RUN apt-get install oracle-java8-installer -y
RUN apt-get install oracle-java8-set-default -y
RUN mkdir /temporary
ADD Client.jar /temporary

WORKDIR /temporary

EXPOSE 15000

ENTRYPOINT /bin/bash

回答2:

You have to find out the docker0 network interface inetAddress to reach to host machine. Try to run ifconfig and check the inetAddr of docker0. Usually it is 172.17.0.1 but it may vary depending on the docker version you are running. That should be enough to talk to the host machine.