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Docker / reverse proxy firmware error, cannot twist another container

I have one host docker that runs 2 web applications inside separate containers. I have a nginx container setup in front of both of them acting as reverse proxies. There are two dns entries for different subdomains pointing to this single host, so I can reach application 1 using app1.domain.com and app2 using app2.domain.com. This setting works fine, and each application is available to the wider universe.

However, app2 should also be able to make an http call to the web services provided by app1. For some reason, http calls to http://app1.domain.com cannot be resolved from the app2 container. curl http://app1.domain.comreturns Failed to connect to app1.domain.com port 80: No route to host.Strangely enough, I can ping app1.domain.com from the app2 container and successfully resolve the host URL. I tried disabling iptables with service iptables stopon the docker host, and this makes the curl and ping commands just hang for a while, before finally returning an error about the unknown host for ping and could not resolve the waving host.

Finally, I can curl from the app2 container to app1 using the docker IP address and port, although this is not an ideal solution, given that he will need to change the way this application is deployed and configured so that this IP address and port can be detected.

UPDATE: output iptables -n -L -v -x

    Chain INPUT (policy ACCEPT 0 packets, 0 bytes)
    pkts      bytes target     prot opt in     out     source               destination
       0        0 ACCEPT     tcp  --  eth1   *       10.191.192.0/18      0.0.0.0/0
     124     6662 ACCEPT     all  --  lo     *       0.0.0.0/0            0.0.0.0/0
       3      120 ACCEPT     tcp  --  eth0   *       0.0.0.0/0            0.0.0.0/0           tcp dpt:3306
  141668 14710477 ACCEPT     tcp  --  *      *       0.0.0.0/0            0.0.0.0/0           tcp dpt:5432
  252325 512668022 ACCEPT     all  --  *      *       0.0.0.0/0            0.0.0.0/0           state RELATED,ESTABLISHED
      31     2635 ACCEPT     icmp --  *      *       0.0.0.0/0            0.0.0.0/0
       0        0 ACCEPT     all  --  lo     *       0.0.0.0/0            0.0.0.0/0
    5496   331240 ACCEPT     tcp  --  *      *       0.0.0.0/0            0.0.0.0/0           state NEW tcp dpt:22
     623    37143 REJECT     all  --  *      *       0.0.0.0/0            0.0.0.0/0           reject-with icmp-host-prohibited

Chain FORWARD (policy ACCEPT 0 packets, 0 bytes)
    pkts      bytes target     prot opt in     out     source               destination
  437791 334335762 DOCKER     all  --  *      docker0  0.0.0.0/0            0.0.0.0/0
  438060 347940196 ACCEPT     all  --  *      docker0  0.0.0.0/0            0.0.0.0/0           ctstate RELATED,ESTABLISHED
  680992 61107377 ACCEPT     all  --  docker0 !docker0  0.0.0.0/0            0.0.0.0/0
     356    24168 ACCEPT     all  --  docker0 docker0  0.0.0.0/0            0.0.0.0/0
       0        0 REJECT     all  --  *      *       0.0.0.0/0            0.0.0.0/0           reject-with icmp-host-prohibited

Chain OUTPUT (policy ACCEPT 604 packets, 125207 bytes)
    pkts      bytes target     prot opt in     out     source               destination
       0        0 ACCEPT     tcp  --  *      eth1    0.0.0.0/0            10.191.192.0/18
     124     6662 ACCEPT     all  --  *      lo      0.0.0.0/0            0.0.0.0/0

Chain DOCKER (1 references)
    pkts      bytes target     prot opt in     out     source               destination
       0        0 ACCEPT     tcp  --  !docker0 docker0  0.0.0.0/0            172.17.0.2          tcp dpt:81
       0        0 ACCEPT     tcp  --  !docker0 docker0  0.0.0.0/0            172.17.0.2          tcp dpt:443
    2191   156283 ACCEPT     tcp  --  !docker0 docker0  0.0.0.0/0            172.17.0.2          tcp dpt:80
       0        0 ACCEPT     tcp  --  docker0 docker0  172.17.0.60          172.17.0.7          tcp dpt:3000
       0        0 ACCEPT     tcp  --  docker0 docker0  172.17.0.7           172.17.0.60         tcp spt:3000

app1 docker ip: 172.17.0.7 app2 docker ip: 172.17.0.60

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You can link your docker containers and then use the link to talk directly to app1 from app2. This way you can avoid dns resolution, and therefore will be faster.

Assuming you run containers like this:

docker run --name app1 app1-image

docker run --name app2 --link app1 app2-image

Now from the app2 container you can access application 1 with the hostname 'app1'

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