Docker - Exposed ports accessible from outside - iptables rules ignored

english
#1

I have a docker container running like:

 docker run --name some_container_1 -p 8080:80 -d some_image

Which works fine. The container exposes it's port 80 to 8080 and is accessible from localhost.

For some reason however it's ignoring the INPUT iptables rules completely and is also accesible from outside.

How can I restrict access to my Docker container to only allow i.e. IP 123.456.789.0 to access it from external?

Thanks.

sudo iptables -L -n -v --line-numbers

Chain INPUT (policy ACCEPT 0 packets, 0 bytes)
num   pkts bytes target     prot opt in     out     source               destination         
1        0     0 ACCEPT     all  --  lo     *       0.0.0.0/0            0.0.0.0/0           
2      365 23380 ACCEPT     all  --  *      *       0.0.0.0/0            0.0.0.0/0            state RELATED,ESTABLISHED
3        0     0 ACCEPT     tcp  --  *      *       0.0.0.0/0            0.0.0.0/0            tcp dpt:22
4        7   788 LOG        all  --  *      *       0.0.0.0/0            0.0.0.0/0            limit: avg 5/min burst 5 LOG flags 0 level 7 prefix "iptables denied: "
5        7   788 DROP       all  --  *      *       0.0.0.0/0            0.0.0.0/0           

Chain FORWARD (policy ACCEPT 0 packets, 0 bytes)
num   pkts bytes target     prot opt in     out     source               destination         
1       24  1524 DOCKER     all  --  *      docker0  0.0.0.0/0            0.0.0.0/0           
2        0     0 ACCEPT     all  --  *      docker0  0.0.0.0/0            0.0.0.0/0            ctstate RELATED,ESTABLISHED
3       15 13320 ACCEPT     all  --  docker0 !docker0  0.0.0.0/0            0.0.0.0/0           
4        0     0 ACCEPT     all  --  docker0 docker0  0.0.0.0/0            0.0.0.0/0           

Chain OUTPUT (policy ACCEPT 204 packets, 21792 bytes)
num   pkts bytes target     prot opt in     out     source               destination         

Chain DOCKER (1 references)
num   pkts bytes target     prot opt in     out     source               destination         
1       24  1524 ACCEPT     tcp  --  !docker0 docker0  0.0.0.0/0            172.17.0.2           tcp dpt:80

sudo iptables-save

# Generated by iptables-save v1.4.21 on Wed Apr  8 23:37:43 2015
*filter
:INPUT ACCEPT [0:0]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [100:16642]
:DOCKER - [0:0]
-A INPUT -i lo -j ACCEPT
-A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT
-A INPUT -p tcp -m tcp --dport 22 -j ACCEPT
-A INPUT -m limit --limit 5/min -j LOG --log-prefix "iptables denied: " --log-level 7
-A INPUT -j DROP
-A FORWARD -o docker0 -j DOCKER
-A FORWARD -o docker0 -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT
-A FORWARD -i docker0 ! -o docker0 -j ACCEPT
-A FORWARD -i docker0 -o docker0 -j ACCEPT
-A DOCKER -d 172.17.0.2/32 ! -i docker0 -o docker0 -p tcp -m tcp --dport 80 -j ACCEPT
COMMIT
# Completed on Wed Apr  8 23:37:43 2015
# Generated by iptables-save v1.4.21 on Wed Apr  8 23:37:43 2015
*nat
:PREROUTING ACCEPT [13:2206]
:INPUT ACCEPT [1:64]
:OUTPUT ACCEPT [4:268]
:POSTROUTING ACCEPT [4:268]
:DOCKER - [0:0]
-A PREROUTING -m addrtype --dst-type LOCAL -j DOCKER
-A OUTPUT ! -d 127.0.0.0/8 -m addrtype --dst-type LOCAL -j DOCKER
-A POSTROUTING -s 172.17.0.0/16 ! -o docker0 -j MASQUERADE
-A POSTROUTING -s 172.17.0.2/32 -d 172.17.0.2/32 -p tcp -m tcp --dport 80 -j MASQUERADE
-A DOCKER ! -i docker0 -p tcp -m tcp --dport 8080 -j DNAT --to-destination 172.17.0.2:80
COMMIT
# Completed on Wed Apr  8 23:37:43 2015

docker info

Containers: 1
Images: 25
Storage Driver: aufs
 Root Dir: /var/lib/docker/aufs
 Backing Filesystem: extfs
 Dirs: 27
Execution Driver: native-0.2
Kernel Version: 3.16.0-4-amd64
Operating System: Debian GNU/Linux 8 (jessie)
CPUs: 4
Total Memory: 7.746 GiB
Name: nuc-001
ID: WCMU:MN3T:VFKR:IU42:6423:OEI6:IB5Q:WBNV:K75H:JZDS:UWU5:57WD
WARNING: No memory limit support
WARNING: No swap limit support
#2

Internally Docker is using iptables to forward connections to the docker host on port 8080 to the service listening on port 80 on the container. The key in your configuration is this line -

-A DOCKER ! -i docker0 -p tcp -m tcp --dport 8080 -j DNAT --to-destination 172.17.0.2:80

By inserting (-I) a new forward line, you can block connections from being forwarded to the container IP, in this case 172.17.0.2. Try this rule -

/sbin/iptables -I FORWARD '!' -s 123.456.789.0 -d 172.17.0.2 -p tcp --dport 80 -j DROP

#3

You can bind the port to your local machine. Then docker will not expose the port to the outside. (iptables)

docker run -p 127.0.0.1:8080:8080 some_image
#4

Wasn’t me, but I think whoever did it thinks this is more of a serverfault question than a programming question. They’re probably right; you might want to migrate it.

#5

Can you show the output of iptables-save? I suspect the way docker does port translation is with an iptables rule via MASQUERADE/NAT, but I don’t actually know

#6

May the downvoter explain?