Docker – Preventing outgoing connection ssh, sftp etc from inside a docker instance

docker

I'm running docker instance 1.6 on CentOS 7. I'm using these instances for development purpose where user can login and do their development work. My requirement is that I do not want any developer to make any sort of outgoing connection from inside the instance. I tried using ip table at host machine but it prevent connection from host machine but not from the docker. Here are the entries available in my iptable.

It will be a big help if you can suggest me a way to stop such connection fro inside a docker container to the outside world without impacting http connection.

# Generated by iptables-save v1.4.21 on Sun Jun 28 23:20:14 2015
*nat
:PREROUTING ACCEPT [6680:929529]
:INPUT ACCEPT [0:0]
:OUTPUT ACCEPT [521:165135]
:POSTROUTING ACCEPT [0:0]
: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
COMMIT
# Completed on Sun Jun 28 23:20:14 2015
# Generated by iptables-save v1.4.21 on Sun Jun 28 23:20:14 2015
*filter
:INPUT ACCEPT [0:0]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [0:0]
: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 -p tcp -m tcp --dport 80:65000 -j ACCEPT
-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 OUTPUT -m state --state RELATED,ESTABLISHED -j ACCEPT
-A OUTPUT -p tcp -m tcp --dport 53 -j ACCEPT
-A OUTPUT -p udp -m udp --dport 53 -j ACCEPT
-A OUTPUT -p tcp -m tcp --dport 80:65000 -j ACCEPT
-A OUTPUT -p tcp -m tcp --dport 80 -j ACCEPT
-A OUTPUT -p tcp -m tcp --dport 443 -j ACCEPT
-A OUTPUT -p tcp -m tcp --dport 6667 -j ACCEPT
-A OUTPUT -p tcp -m tcp --dport 6697 -j ACCEPT
-A OUTPUT -j DROP
COMMIT
# Completed on Sun Jun 28 23:20:14 2015

Best Answer

You need to work in your FORWARD CHAIN, because the DOCKER traffic goes docker -> your host interface

for example, I need to block my http traffic inside the docker.

iptables -A FORWARD -i virbr0 -p tcp -d 0/0 --dport 80 -m conntrack --ctstate NEW -j DROP

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No, you can't do it straight forward.

You can do one of the following:

Make your web container communicate with ffmpeg container using RPC/agent.
Use queue service, so your ffmpeg container listen to the queue job.
Run docker inside docker.

Iptables – Whitelisting outgoing traffic from docker containers

The trick is to get iptables to redirect only the connections from the DEV Env containers. We can do this by adding a rule to accept all connections from the Reverse Proxy. So the IP table rules will now become:

-A PREROUTING -i docker0 -s 172.17.0.2/32 -j ACCEPT
-A PREROUTING -i docker0 -s 172.17.0.1/32 -j ACCEPT
-A PREROUTING -i docker0 -p tcp -d 0/0 -j REDIRECT --to-port 3128

Since docker dynamically allocates IPs. The IPs used will need to be updated if the docker containers are rerun or the server is restarted. I also added the rule for 172.17.0.1 which is the docker0 ip.

These rules mean that all other traffic originating from the docker0 interface, other than the reverse proxy container and docker host itself, get redirected to squid.

Within squid we can whitelist domain as we like by using the following lines

acl allowed_domain dstdomain google.com
http_access allow allowed_domain

full iptables rules are:

# Generated by iptables-save v1.4.21 on Fri Nov  6 18:54:09 2015
*nat
:PREROUTING ACCEPT [30:1796]
:INPUT ACCEPT [28:1680]
:OUTPUT ACCEPT [37:2388]
:POSTROUTING ACCEPT [46:2964]
:DOCKER - [0:0]
-A PREROUTING -m addrtype --dst-type LOCAL -j DOCKER
-A PREROUTING -i docker0 -s 172.17.0.2/32 -j ACCEPT
-A PREROUTING -i docker0 -s 172.17.0.1/32 -j ACCEPT
-A PREROUTING -i docker0 -p tcp -d 0/0 -j REDIRECT --to-port 3128
-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 172.17.0.3/32 -d 172.17.0.3/32 -p tcp -m tcp --dport 8000 -j MASQUERADE
-A POSTROUTING -s 172.17.0.3/32 -d 172.17.0.3/32 -p tcp -m tcp --dport 80 -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 9000 -j DNAT --to-destination 172.17.0.3:8000
-A DOCKER ! -i docker0 -p tcp -m tcp --dport 8192 -j DNAT --to-destination 172.17.0.3:80
-A DOCKER ! -i docker0 -p tcp -m tcp --dport 80 -j DNAT --to-destination 172.17.0.2:80
COMMIT
# Completed on Fri Nov  6 18:54:09 2015
# Generated by iptables-save v1.4.21 on Fri Nov  6 18:54:09 2015
*filter
:INPUT ACCEPT [1891:3910112]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [1500:1500230]
:DOCKER - [0:0]
-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 172.17.0.3/32 ! -i docker0 -o docker0 -p tcp -m tcp --dport 8000 -j ACCEPT
-A DOCKER -d 172.17.0.3/32 ! -i docker0 -o docker0 -p tcp -m tcp --dport 80 -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 Fri Nov  6 18:54:09 2015

full squid rules are:

acl SSL_ports port 443
acl Safe_ports port 80      # http
acl Safe_ports port 21      # ftp
acl Safe_ports port 443     # https
acl Safe_ports port 70      # gopher
acl Safe_ports port 210     # wais
acl Safe_ports port 1025-65535  # unregistered ports
acl Safe_ports port 280     # http-mgmt
acl Safe_ports port 488     # gss-http
acl Safe_ports port 591     # filemaker
acl Safe_ports port 777     # multiling http
acl CONNECT method CONNECT
http_access deny !Safe_ports
http_access allow localhost manager
http_access deny manager
acl allowed_domain dstdomain google.com
http_access allow allowed_domain
http_access allow localhost
http_access deny all
http_port 3128 accel vhost allow-direct
coredump_dir /var/spool/squid3
refresh_pattern ^ftp:       1440    20% 10080
refresh_pattern ^gopher:    1440    0%  1440
refresh_pattern -i (/cgi-bin/|\?) 0 0%  0
refresh_pattern (Release|Packages(.gz)*)$      0       20%     2880
refresh_pattern .       0   20% 4320

Best Answer

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