Can't connect to a docker container port where

Question

I want to run Jenkins, but to demonstrate the problem, I'm running a netcat server container in Ubuntu 15.10:

Docker version 1.6.2, build 7c8fca2

Here's my Dockerfile:

FROM ubuntu
CMD while true; do echo 'HTTP/1.1 200 OK\r\n\r\nHello world' | nc -l 8080; done

When run on the host, this one-liner will return HTTP 200 responses.

Now, on the container. Ran docker build -t mydoc .. Ran docker run -it --expose 8080 -p 8080:8080 mydoc. In another terminal, tried to curl it: curl -D - -o - http://127.0.0.1:8080.

It just blocks with no response.

Some possibly relevant info:

>docker ps
CONTAINER ID        IMAGE               COMMAND                CREATED             STATUS              PORTS                    NAMES
1acc13bb3384        mydoc:latest        "/bin/sh -c 'while t   48 seconds ago      Up 47 seconds       0.0.0.0:8080->8080/tcp   goofy_darwin        

and

>netstat -ant | grep 8080
tcp        0      1 10.0.2.15:34512         172.17.0.25:8080        SYN_SENT   
tcp        0      0 127.0.0.1:33276         127.0.0.1:8080          ESTABLISHED
tcp6       0      0 :::8080                 :::*                    LISTEN     
tcp6      78      0 127.0.0.1:8080          127.0.0.1:33276         ESTABLISHED

Note the SYN_SENT. That's as far as it gets.

Answer 1

The Linux service status showed as:

● docker.service - Docker Application Container Engine
   Loaded: loaded (/lib/systemd/system/docker.service; enabled; vendor preset: enabled)
   Active: active (running) since Mon 2016-03-07 13:39:44 CST; 2min 24s ago
     Docs: http://docs.docker.com
 Main PID: 672 (docker)
   Memory: 11.2M
      CPU: 62ms
   CGroup: /system.slice/docker.service
           └─672 /usr/bin/docker -d -H fd://

This fixed the issue:

service docker restart

I don't know why. Now the service responds:

>curl -D - http://127.0.0.1:8080
HTTP/1.1 200 OK

Hello world

Also, the option --expose 8080 was not necessary for this to work.

EDIT:

After getting 1.6.2 to work, I upgraded to 1.10.2 and haven't seen this problem yet. I suspect some kind of race condition on host startup, but can't say for sure. Maybe the docker service script needs a Required-Start: $network or something.