Fedora KVM with simple network forwards

June 02, 2010 at 10:52 PM | categories: Servers, Linux | View Comments

Recently I've been teaching python to some high school students. It has been going well, but the development environment we had access to left a little bit to be desired. We were working with ages old solaris, vi only, and no real access to newer gnu (or other) tools. So a new setup was required, I went off to investigate.

I started with chroot, since a buddy, Daniel Thau, had used it extensively for running multiple operating systems side by side. He'd pointed me in the directions of febootstrap and that seemed like it'd work fine. I was able to make a sandbox, get ssh running on 2022 and then have my dlink route that to my box. Success!

But I found that a bit messy, and a bit limited. I wanted to lock down how much of my resources they could use, and I didn't want to have to give access to some of my root file systems directly; /proc, /dev, etc. So I looked around a bit more, and stumbled on using KVM indirectly via the new virt-manager toolset that fedora 12 and 13 provide. Installation was as simple as:

$ yum install qemu-kvm virt-manager virt-viewer python-virtinst

But it also seems that from the techotopia article I followed for some of this that one could also just do:

$ yum groupinstall 'Virtualization'

I have to say it's a pretty swank set of tools. It's free, it works on KVM or Xen. KVM usage requires no special kernel and as such, no reboot. The setup was simple, and gave out a vnc port to connect to from the get go. It is also trivial to connect to a setup on machine A with virt-manager on machine B over ssh. If you want more information, fedora has a nice writeup, and libvirt has a more distro agnostic set of docs.

Problem was though that the networking was virtual, and didn't pull an IP address from my router, so it wasn't public. There were a few sections here and there describing how to switch to bridged, and I tried them. They didn't work for me, either I suck at following directions, or they just won't work how I expect them to. You can see for yourself here at how I attempted network bridging.

What I did was much more in my realm of knowledge, is simpler than all the other options, and is something I can make changes to w/o killing my network connectivity. iptables! I just used NAT forwarding. It was 2 lines, put in my pre-existing firewall script. So to get my local box on port 2022 to forward to its internal virtual network of at port 22 was as plain as this:

$ iptables -t nat -I PREROUTING -p tcp --dport 2022 -j DNAT\
$ iptables -I FORWARD -p tcp --dport 22 -d -j ACCEPT

One preroute rule to grab the port incoming, and one forward rule to pass said packets along. Now I have connectivity into my class virtual machine, and I don't have to do much to add more ports as needed. I am pretty happy with the setup so far. It's really nice to be able to connect remotely, vnc or ssh now, as well as know that I've limited the ram and cpu time the class can use on my box. I am interested to hear if anyone else is doing similar things with virtualization on their desktops.

Trac makes my life easy

July 22, 2009 at 05:15 PM | categories: Servers, Linux | View Comments

The project management app Trac is something that was new to me a while back. I'd just installed t for a side project, and used the yum install without any issues. It took care of all the grunt work, and got me to the point where I could now create and use a trac project.

Trac is set up like what I see web frameworks go with. A main program that will install the framework in a project directory. In this case trac-admin , which is killer when you want to make multiple projects, and offers a cli interface to the project s framework configuration, etc.

This setup becomes awesome I found when you want to upgrade. Yum installed what it had packaged, the .10 version, but I had decided that I wanted to toy with bitten their automated build tool, which required .11 and up. So an upgrade was needed, yum couldn t be used, but I found that trac-admin has an upgrade command.

So I was poised to make the fun and scary transition into mixing a package managed install with a source install, not something that always goes well. I ve found that sometimes packagers change to install location from where the src install goes (looking at you nagios), and make some conflicts or at least confusion.

The upgrade process for the server then my app was as simple as:

wget http://ftp.edgewall.com/pub/trac/Trac-0.11.5.tar.gz
tar zxvf http://ftp.edgewall.com/pub/trac/Trac-0.11.5.tar.gz
cd Trac-0.11.5
python setup.py install
trac-admin /path/to/project upgrade
trac-admin /path/to/project wiki upgrade
/etc/init.d/httpd restart

This blew me away. I ve have never had a complicated app (relativily of course) upgrade so simply, and without any issues. The main install of trac from empty folder to working project manager was simple too, so perhaps I should have expected this, but really I think it is a testimony to how well the developers of Trac have though of the whole process of using their framework.

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