Restrict Internet Access - Docker Container - docker

Question

I have a situation to restrict internet access of the container in load balancer network. for example in that below picture
Only container4 connects to the Internet; other three only communicate through container4 with the outside world. For example if container1 needs smtp support, it will forward smtp request to container4 to get access.
No container other than container4 should be allowed to access the Internet directly! This should be enforced on Docker level.
I believe it will be configurable on docker network creation, can any one explain how to achieve this?

Answer 1

As found here, I got this to work with docker-compose. Save as docker-compose.yml:
version: '3'
services:
outgoing-wont-work:
image: alpine
networks:
- no-internet
command: ping -c 3 google.com # will crash
internal-will-work:
image: alpine
networks:
- no-internet
command: ping -c 3 internal-and-external
internal-and-external:
image: alpine
networks:
- no-internet
- internet
command: ping -c 3 google.com
networks:
no-internet:
driver: bridge
internal: true
internet:
driver: bridge
Then run docker-compose up -d, docker-compose ps will show something like this after a few seconds:
Name Command State Ports
----------------------------------------------------------------------------------
dco_inet_internal-and-external_1 ping -c 3 google.com Exit 0
dco_inet_internal-will-work_1 ping -c 3 internal-and-ext ... Exit 0
dco_inet_outgoing-wont-work_1 ping -c 3 google.com Exit 1

Answer 2

Network creation for access internet
docker network create --subnet=172.19.0.0/16 internet
Network creation for block internet access
docker network create --internal --subnet 10.1.1.0/24 no-internet
If you want to connect docker container into internet
docker network connect internet container-name
If you want to block internet access
docker network connect no-internet container-name
Note
in internal network we can't expose ports to connect outside world, please refer this question for more details

Answer 3

Another option, if you need to expose ports on a container without internet access, but want to let it talk to other containers would be to provide a bogus DNS configuration. This isn't a perfect solution though, since it doesn't prevent direct IP access to the outside world.
docker-compose.yaml
version: '3'
services:
service1:
image: alpine
command: sh -c 'ping service2 -c 1; ping google.com -c 1'
dns: 0.0.0.0
service2:
image: alpine
command: sh -c 'ping service1 -c 1; ping google.com -c 1'
dns: 0.0.0.0
isolated> docker-compose up
Recreating isolated_service1_1 ... done Recreating isolated_service2_1 ... done Attaching to isolated_service2_1, isolated_service1_1
service1_1 | PING service2 (172.18.0.2) 56(84) bytes of data.
service1_1 | 64 bytes from isolated_service2_1.isolated_default (172.18.0.2): icmp_seq=1 ttl=64 time=0.038 ms
service1_1 |
service1_1 | --- service2 ping statistics ---
service1_1 | 1 packets transmitted, 1 received, 0% packet loss, time 0ms
service1_1 | rtt min/avg/max/mdev = 0.038/0.038/0.038/0.000 ms
service2_1 | PING service1 (172.18.0.3) 56(84) bytes of data.
service2_1 | 64 bytes from isolated_service1_1.isolated_default (172.18.0.3): icmp_seq=1 ttl=64 time=0.093 ms
service2_1 |
service2_1 | --- service1 ping statistics ---
service2_1 | 1 packets transmitted, 1 received, 0% packet loss, time 0ms
service2_1 | rtt min/avg/max/mdev = 0.093/0.093/0.093/0.000 ms
service1_1 | ping: google.com: Temporary failure in name resolution
service2_1 | ping: google.com: Temporary failure in name resolution
isolated_service1_1 exited with code 2
isolated_service2_1 exited with code 2

Answer 4

As stated in Bilal's answer, the internal network is a good solution if you do not need to expose the ports.
If you do need to expose the ports, the below solution using iptables does the job for my requirements:
docker network create --subnet 172.19.0.0/16 no-internet
sudo iptables --insert DOCKER-USER -s 172.19.0.0/16 -j REJECT --reject-with icmp-port-unreachable
sudo iptables --insert DOCKER-USER -s 172.19.0.0/16 -m state --state RELATED,ESTABLISHED -j RETURN
Then add
--network no-internet
when you run your docker container. For instance:
$ docker run -it --network no-internet ubuntu:focal /bin/bash
root#9f2181f79985:/# apt update
Err:1 http://archive.ubuntu.com/ubuntu focal InRelease
Temporary failure resolving 'archive.ubuntu.com'