packstack – Cinder and Nagios Options, and Advanced Operation

After getting a grasp on all of the concepts that I have discussed regarding OpenStack, I have decided to give my dev server a re-deploy, namely to set up LVM for proper use with Cinder.

I noticed a few things that should probably be noted when using packstack to configure an OpenStack host.

First off, packstack is not necessarily just for setting up lab environments. By running packstack –help, the program will output a plethora of options that can be used for controlling how packstack runs. This can be used to limit deployment to just a few options, so that, for example, it only deploys a compute node, or a storage node, etc. It also allows for answer file use. With fine-tuning of the options, packstack can be used to configure entire clouds, or at the very least more sophisticated multi-server labs.

Another thing to note is that there are several options that are set by default that may not be desired. For example, ultimately my second run at at an OpenStack all-in-one is looking like this:

packstack --allinone --provision-all-in-one-ovs-bridge=n --cinder-volumes-create=n --nagios-install=n

This excludes the following:

  • The Open vSwitch bridge setup. This is because I want to re-configure the Open vSwitch bridges again as per this article.
  • Creation of the test Cinder volume group – I already have one created this time around that I want to use with Cinder. This is named cinder-volumes as per the default volume group that Cinder looks for, and is also the volume group that packstack will create with raw file on the file system, which is not suitable for production use. If you have this volume group set up already and do not select this flag, packstack will ultimately fail.
  • Disabling the installation of a full Nagios monitoring suite on the host, as I plan to set up monitoring later – and not with Nagios, mind you!

Remember that you can check out a brief rundown on how to install and use packstack at the quickstart page on RDO.

CentOS ifcfg Scripts: DEVICE vs NAME

In the previous article that I discussed setting up Open vSwitch in, I encountered an odd issue when setting up my bridges for configuration upon startup (especially the br-ex bridge, which I had a management address on as well). Restarting the network after the initial changes worked, but upon startup, the network did not come up properly. After logging in and restarting the network again, things came up. This process was reproducible 100% of the time.

Upon startup, only the OvS bridges were up. Physical interfaces were not added. Upon initial inspection there did not seem to be anything wrong, so I started to delve into the process further and spent a morning of googling and poring thru the network init scripts, trying to figure out exactly what I did wrong, or if there was a bug with the way OvS auto-configuration was handled on RedHat-family systems.

The answer? Yes and no.

Ultimately there was an error in my configuration. In my physical interface config file (ie: ifcfg-eth0 or its equivalent in the new PCI syntax CentOS and RHEL 7 follow), I had:

NAME="eth0" <-- BAD

The correct file has:

DEVICE="eth0" <-- GOOD

Basically, the issue was the presence of the NAME directive in place of the correct DEVICE directive.

The Cause

I’m pretty sure NAME was there from installation. I performed minimal modification of the physical interface configuration file, and my bridge configuration file had the correct syntax (which I took from a tutorial, save the actual addressing information which I transplanted from the physical interface).

After poring over logs, I found the giveaway:

Feb 9 10:39:52 devhost network: Bringing up interface eth0: Error: either "dev" is duplicate, or "br-ex" is a garbage.
Feb 9 10:39:52 devhost network: cat: /sys/class/net/eth0: Is a directory
Feb 9 10:39:52 devhost network: cat: br-ex/ifindex: No such file or directory
Feb 9 10:39:52 devhost network: /etc/sysconfig/network-scripts/ifup-eth: line 273: 1000 + : syntax error: operand expected (error token is "+ ")
Feb 9 10:39:52 devhost network: ERROR : [/etc/sysconfig/network-scripts/ifup-aliases] Missing config file br-ex.
Feb 9 10:39:52 devhost /etc/sysconfig/network-scripts/ifup-aliases: Missing config file br-ex.
Feb 9 10:39:52 devhost ovs-vsctl: ovs|00001|vsctl|INFO|Called as ovs-vsctl -t 10 -- --may-exist add-port br-ex "eth0
Feb 9 10:39:52 devhost ovs-vsctl: br-ex"
Feb 9 10:39:53 devhost network: [ OK ]

There was a line break in the ovs-vsctl command logged in syslog.

I ultimately traced this down to the get_device_by_hwaddr() function, in /etc/sysconfig/network-scripts/network-functions:

get_device_by_hwaddr ()
    LANG=C ip -o link | awk -F ': ' -vIGNORECASE=1 '!/link\/ieee802\.11/ && /'"$1"'/ { print $2 }'

This will return multiple interfaces, separated by line breaks, when there is more than one interface on the system sharing a MAC address. Using DEVICE instead of NAME skips this, as the system only runs this when the former is not defined.

The MAC address got duplicated probably from a previous setup of OvS and was retained when the bridge was brought back up upon startup.

Moral of the story: if you are setting up bridging or any other kind of virtual interface infrastructure after installation, don’t overlook this, to save yourself some pain!

I posted a bug to CentOS about this as well:

An Intro to Open vSwitch

I’ve spent the last few days getting my bearings around Open vSwitch. It’s pretty amazing, and IMO if you are virtualizing under Linux these days, it’s pretty much a must.

So what is Open vSwitch? It’s basically the Open Source answer to other proprietary technologies, such as VMware’s distributed vSwitch (which you have probably used if you have ever used multiple servers within vSphere). It allows you to build a distributed layer-2 network entirely in software. It also performs very well under a single server setup, allowing you to build sophisticated switch fabrics under a single physical interface. It solves some frustrations surrounding network bridging under a KVM setup as well that you may have encountered, such as having a bridge that shares the same physical interface as your host’s management address.

Check out for some documentation and tutorials.

I will be explaining some basic concepts regarding Open vSwitch here, namely how to set up a bridge, attach an interface to it, and also how to automate the process using ifcfg-* files under CentOS (and by proxy, probably RHEL and Fedora as well). Also, we will discuss how to set up a VM on the bridge using libvirt.

Some Terms

bridge is a network fabric under Open vSwitch. For the purpose of this tutorial, a bridge represents a broadcast domain within the fabric at large, ie: a VLAN. Note that this does not have to be the case all the time, as it is possible to have a bridge that has ports on different VLANs, just like a physical switch.

port is a virtual switch port within the bridge. These ports are attached to interfaces, such as physical ones, virtual machine interfaces, or other bridges.

Open vSwitch Basic Bridge

Above is a very simple diagram that depicts the bridge br-ex, with ports connected to a VM’s eth0, and the host machine’s eth0.

Creating a Bridge

Run the following command to create a bridge:

ovs-vsctl add-br br-ex

This command would create a new empty bridge, br-ex. This bridge can then be addressed just like a regular interface on the system, but of course, would not do much at this point in time since we do not have any ports attached to it.

Adding a Port

ovs-vsctl add-port br-ex eth0

This would add eth0 to the bridge br-ex.

CentOS/RedHat/Fedora Interface Configuration Files

You can also have the OS set up bridges for you upon system startup – this is especially useful if you are binding IP addresses to a specific bridge. Note that any bridges that you create like this will get destroyed/re-created upon restart of the network (ie: system network restart or systemctl restart network.service).

Change your ifcfg-eth0 file to look something like this:


And create a ifcfg-br-ex interface configuration file:


Sub in your values for MAC addresses, physical interface names, and IP addresses, obviously.

Another note here that is extremely important is that you need to make sure that you use the DEVICE directive instead of the NAME directive. The latter may be left over in your physical interface configuration file from installation, so make a note to change it. I will address the exact reason why in a different article.

Setting Up a Libvirt VM to use a Bridge

Now that you have set up the above, you can add a VM to the bridge with Libvirt. Edit your domain’s (VM’s) XML file and add a block like this for every NIC you want to create:

 <interface type='bridge'>
  <mac address='52:54:00:71:b1:b6'/>
  <source bridge='br-ex'/>
  <virtualport type='openvswitch'/>
  <address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>

This was taken directly from the Open vSwitch Libvrirt HOWTO.

Make sure of course that you assign a correct PCI ID. You may wish to create the domain first via other means, add the devices you will need, and just elect to not use network at first. Unfortunately, it does not seem that a lot of Libvirt admin tools have specific Open vSwitch support just yet (at least it does not seem that the version of virt-manager that comes with most distributions does, anyway).

Edit Feb 12 2015 – Slight correction to physical interface config file – duplicate device type.

Adventures in OpenStack – RDO Juno Install, and Debian Images

Been playing with OpenStack a bit the last few days. I have had a bit of a busy spell so I have not had too much time to play with it as much as I wanted to, but some things to note:

These two things are going to make the setup of my home lab much more pleasant, I will have to say. 🙂