Changes
Moved link to HN definition at its first occurence, for anyone confused by the acronym
This document consists of two parts. The first is setting up a firewall (using iptables) on the [[HN]], which will restrict traffic to the containers. The effect would emulate, as far as the containers and their customers are concerned, an external hardware firewall controlled by the sysadmin. The second is setting up a firewall that protects the HN itself but still allows traffic to the containers, thus allowing individual containers to define their own iptables.
While the firewalls shown here can be accomplished using iptables manually (or using Fedora core's iptables service), the methods presented here are especially modular and easy to modify. This is important when you have 20+ containers and a lot of other things to be doing...
The exception to this is the nameserver, which we want open to the world. We use it as a caching nameserver for our containers and also to host DNS for a few customer domain.
== Simple firewall configuration independent of IP addresses: vzfirewall ==
<code>Vzfirewall</code> tool allows you to open/close ports for incoming connections with no dependencies to foreign IP addresses. E.g. you may allow a hostname <code>release.prod.example.com</code> to connect to port 5432 of VE 1234 and leave all other ports closed by modifying <code>1234.conf</code> file adding multiline <code>FIREWALL</code> directives into it:
<pre>
...
PRIVVMPAGES="300000:300000"
HOSTNAME="example.com"
...
FIREWALL="
...
# Allow access to PostgreSQL port only from release.prod
# and release.test machines. You may use domain names here.
[5432]
release.prod.example.com
release.test.example.com
...
"
</pre>
You must then run <code>vzfirewall -a</code> on your hardware node to apply changes made in <code>*.conf</code>.
Note that it is recommended to use hostnames instead of IP addresses here, so the configuration is persistent for VE movements to different IP-address: you just need to run <code>vzfirewall -a</code> again after movement. It is also reboot-safe, as the rules are applied to <code>/etc/sysconfig/iptables</code> (at RHEL systems).
Vzfirewall and its documentation are available at [http://en.dklab.ru/lib/dklab_vzfirewall/ http://en.dklab.ru/lib/dklab_vzfirewall/].
== An alternative from the author of Shorewall ==
For those who might find the solution provided in this wiki article unsatisfactory (for whatever reason), the creator of Shorewall (Tom Eastep) has written a nice article explaining how to use Shorewall on an OpenVZ host node to manage the host node, containers, and more... with quite a complex setup as an example. The article IS NOT an introduction to Shorewall for beginners, so some pre-existing knowledge and understanding of Shorewall may be required.
Shorewall and OpenVZ by Tom Eastep - http://www.shorewall.net/OpenVZ.html
See also this OpenVZ Forum posting - http://forum.openvz.org/index.php?t=msg&goto=16406&
== Setting up a HN-based firewall ==
#!/bin/sh
# firewall Start iptables firewall
# chkconfig: 2345 08 9297 87
# description: Starts, stops and saves iptables firewall
# This script sets up the firewall for the INPUT chain (which is for
# /etc/firewall.d to set up additional rules in the FORWARD chain
# to allow access to containers' services.
# http://wiki.openvz.org/Setting_up_an_iptables_firewall
. /etc/init.d/functions
;;
esac
</pre>
Note: This will only allow access to the HN from the hosts/networks defined in SEGMENT. If you'd like to open up the OKPORTS on the HN to everybody, you can remove the ''-s $SEGMENT'' parameters from the iptables commands under the "Firewall: Allowing access to HN" section. The modified lines would look like this:
<pre>
iptables -I INPUT -j ACCEPT -d $THISHOST --protocol tcp --destination-port $port
iptables -I INPUT -j ACCEPT -d $THISHOST --protocol udp --destination-port $port
</pre>
</pre>
And there you go. Note: You can only put one IP address inside the CTIP variable, but if your container has multiple IP addresses you can create a copy of the file for each IP address. Go ahead and start the firewall and check its status:
<pre>
service firewall restart
As you can see, you can now add and edit the configurations for individual containers very easily. This method proves a lot easier to manage than Fedora's iptables-config mechamism!
To make the firewall service automatically start when the HN boots, run
<pre>
chkconfig --add firewall
</pre>
=== Debian Notes ===
The setup above works fine for Debian as well, however /etc/init.d/functions is missing. Here is a very simple version that you can use:
# /etc/init.d/functions
success() {
echo -n "...success"
}
failure() {
echo -n "...failure"
}
== Setting up a firewall that allows per-container configuration ==
This setup configures iptables on the HN to disallow access to all hosts, including the containers. However, it allows all traffic into the containers so they may define their own iptables rules and therefore manage their own firewall.
<codepre>This content is missing. You are invited to fill it in, if you get to it before I do. :)iptables -P FORWARD ACCEPTiptables -F FORWARD</codepre> This will remove all rules for the FORWARD chain so all packets can pass back and forth between containers and the outside world.
If you want to use a firewall inside a container, please load these modules BEFORE starting the container:
<codepre>
modprobe xt_tcpudp
modprobe ip_conntrack
</codepre>
If you do not, you will get an error like this: "iptables: No chain/target/match by that name"
* Note: xt_tcpudp module seem to be included in the kernel packages of Debian 6, but not of CentOS 6.
If you want to use stateful firewall rules (and you should!) you will also need to make sure that 'ipt_state' is in the 'IPTABLES' option in your vz.conf file:
<pre>
IPTABLES="ipt_REJECT ipt_tos ipt_limit ipt_multiport iptable_filter iptable_mangle ipt_TCPMSS ipt_tcpmss ipt_ttl ipt_length ipt_state"
</pre>
Also make sure the 'xt_state' module is loaded on the host:
<pre>
modprobe xt_state
</pre>
Above information is outdated, to enable iptables you need to make sure that CT.conf(CT - id of your container, 100 for example) contains following line:
<pre>
NETFILTER="full"
</pre>
When this done, you should reboot your container and iptables should work properly.
== See also ==
* [[Traffic accounting with iptables]]
* [http://www.readymakers.com/blog/how-to-enable-iptables-in-openvz-container/ How to enable IPtables in OpenVZ container] (Frank Taveras) - Lack of modprobe modules on HN.
[[Category: Networking]]