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Adding FIREWALL to Docker

manish srivastava
Director & CEO, GDP CHURN (P) Ltd. Loves coding . Supports open source by funding.
・2 min read

This is going to solve problems of many Devops engineers looking for Firewall Security for their containers.

Following are my previous articles on Docker Security:

and

Docker does not prevent one from doing Host Firewall implementation; rather, it adds to the complexity. This guide is indented to add host firewall to docker.

STEP 1

(a)Navigate to /etc/systemd/system/ and create a directory named docker.service.d
(b) create a file noiptables.conf and add the following content:

[Service]
ExecStart=
ExecStart=/usr/bin/docker daemon -H fd:// --iptables=false
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STEP 2

(a) Restart Docker
(b) check iptables -L -n -v (If everything Okay you will not see any rules :) )

STEP 3

(a) RUN apt-get install iptables-persistent

After running this, you will be prompted to save your IPv4, and then your IPv6 rules to two files, /etc/iptables/rules.v4 and /etc/iptables/rules.v6 respectively.

In order to give IPv4 Internet Access to all the containers, the server must perform NAT.To do that, in the beginning of the rules.v4 file, add the following:

*nat
:PREROUTING ACCEPT [0:0]
:INPUT ACCEPT [0:0]
:OUTPUT ACCEPT [0:0]
:FORWARD ACCEPT [0:0]
:POSTROUTING ACCEPT [0:0]
-A POSTROUTING -o eth0 -j masquerade
COMMIT
And then below it, 
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After you’re finished, your rules.v4 / rules.v6 file will look something like this:

*nat
:PREROUTING ACCEPT [0:0]
:INPUT ACCEPT [0:0]
:OUTPUT ACCEPT [0:0]
:POSTROUTING ACCEPT [0:0]

-A POSTROUTING -o eth0 -j MASQUERADE

COMMIT

*filter
:INPUT ACCEPT [0:0]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [0:0]

# Allow localhost
-A INPUT -i lo -j ACCEPT
-A OUTPUT -o lo -j ACCEPT

# ICMP
-A INPUT -p icmp -j ACCEPT

# Docker
-A FORWARD -i docker0 -o eth0 -j ACCEPT
-A FORWARD -i eth0 -o docker0 -j ACCEPT

# Incoming
-A INPUT -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT

-A INPUT -p tcp -m tcp --dport 22 -j ACCEPT
-A INPUT -p tcp -m tcp --dport 80 -j ACCEPT
-A INPUT -p tcp -m tcp --dport 443 -j ACCEPT
-A INPUT -j DROP

# Outgoing
-A OUTPUT -j ACCEPT

# Routing
-A FORWARD -j DROP

COMMIT
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Of course, you must replace eth0 with your outbound network interface if it is different than eth0.
After you complete that, restart the firewall via netfilter-persistent reload, and you’re good to go!

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