OpenStack Nova CentOS Instance

I’ve been working on tweaking a CentOS 5.3 image you can download from http://open.eucalyptus.com/wiki/EucalyptusUserImageCreatorGuide_v1.6 as there seems to be a big bias towards running Ubuntu under OpenStack. This is great for getting OpenStack up and running, but for us evangelists that operate a RHEL family house, its crucial to be able to demonstrate like-for-like offerings against what you currently run to help promote its use.

This guide should get you to a point where you have a usable, useful CentOS image for your environment. When I get around to it I’ll upload my version for use in your environment with the modifications laid out in this blog post.

The Guide

  • Start off by downloading a compatible image from Eucalyptus: http://open.eucalyptus.com/wiki/EucalyptusUserImageCreatorGuide_v1.6. I’ll work on the 64-Bit CentOS 5.3 image for this guide.
  • mkdir cloud/images and unpack the tarball here
    • mkdir -p cloud/images
    • cd cloud/images
    • tar zxvf <path_to_tarball>/euca-centos-5.3-x86_64.tar.gz
    • cd euca-centos-5.3-x86_64
    • At this stage we’d normally upload the image to OpenStack but some modifications are needed such as increasing the size of the image to accommodate some new packages so we must first mount the image (read-only because we’re not needing to make edits to this yet) as follows
      • mkdir image
      • sudo mount centos.5-3.x86-64.img image -o loop,ro
    • Increase the size of the image as follows and copy the contents
      • dd if=/dev/zero of=newcentos.img bs=1M count=2048
      • mkfs.ext3 newcentos.img
      • mkdir newcentos
      • sudo mount newcentos.img newcentos -o loop,rw
      • sudo cp -pR image/* newcentos/
      • sudo umount image
  • Modify the image as follows
  • IMPORTANT! (ensure you’re chrooted as described below to your mounted image and you have verified that you’re not modifying your running environment – I accept no responsibility because you can’t read)
    • sudo su -
    • chroot ~/cloud/images/euca-centos-5.3-x86_64/newcentos
    • mount proc -t proc /proc
  • Now to modify the image and install some new packages…
    • yum update
    • yum install redhat-lsb sudo enhanced-vim
    • Remove /etc/udev/rules.d/* to stop the lengthy wait on boot
    • edit /etc/sysconfig/network and disable ZEROCONF (your instance will fail to download meta data from OpenStack nova-api otherwise)
      • NOZEROCONF=yes
    • Edit /etc/profile.d/vim.sh
      • if [ -n "$BASH_VERSION" -o -n "$KSH_VERSION" -o -n "$ZSH_VERSION" ]
        then
        [ -x /usr/bin/id ] || return
        tmpid=$(/usr/bin/id -u)
        [ "$tmpid" = "" ] && tmpid=0
        # for bash and zsh, only if no alias is already set
        alias vi >/dev/null 2>&1 || alias vi=vim
        alias view >/dev/null 2>&1 || alias view='vim -R'
        fi
    • Ensure /dev/null is writeable by all
      • chmod 777 /dev/null
  • That’s the modifications done, but feel free to add your own to suit your own environment so to wrap it up
    • umount /proc
    • logout
    • logout
    • sudo umount newcentos
    • To make things neat rename it appropriately
      • mv newcentos.img centos-5.5-x86_64.img

Upload CentOS image to OpenStack

  • Now you have a CentOS image suitable for OpenStack you need to upload it to OpenStack.
  • The tarball ships with 2 lots of kernels and ramdisks. I’ll assume you’ll be using KVM, but change the instructions to suit a Xen hypervisor.
    • Upload the kernel and make note of the ami
      • euca-bundle-image -i kvm-kernel/vmlinuz-2.6.28-11-generic
        --kernel true
      • euca-upload-bundle -b mybucket
        -m /tmp/vmlinuz-2.6.28-11-generic.manifest.xml
      • euca-register mybucket/vmlinuz-2.6.28-11-generic.manifest.xml
    • Upload the ramdisk and make a note of the ami
      • euca-bundle-image -i kvm-kernel/initrd.img-2.6.28-11-generic
        --ramdisk true
      • euca-upload-bundle -b mybucket
        -m /tmp/initrd.img-2.6.28-11-generic.manifest.xml
      • euca-register mybucket/initrd.img-2.6.28-11-generic.manifest.xml
    • Upload the machine image you modifed above, specifying the ami values from the steps above to specify the kernel and ramdisk to load with this
      • euca-bundle-image -i centos-5.5-x86_64.img
        --kernel aki-XXXXXXXX --ramdisk ari-XXXXXXXX
      • euca-upload-bundle -b mybucket
        -m /tmp/centos-5.5-x86_64.img.manifest.xml
      • euca-register mybucket/centos-5.5-x86_64.img.manifest.xml
  • That’s it done (you may have to wait a short while whilst it uploads to the nova-objectstore server) – you should now see your new AMI available
    • euca-describe-images
      • IMAGE    ami-reey5wk5    mybucket/centos.5-5.x86-64.img.manifest.xml   
        myproject    available    private        x86_64    machine    ami-f4ks8moj   
        ami-jqxvgtmd
  • You can now use this to launch an instance
    • euca-run-instances ami-reey5wk5 -k openstack -t m1.tiny
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7 comments on “OpenStack Nova CentOS Instance

  1. Thanks for posting the Centos image upload instructions.

    The centos image does not have /etc/resolv.conf. yum update failed to find any of the repo hosts. I created /etc/resolv.conf and added “nameserver” lines. I had to issue: “yum clean all;yum clean metadata” and then “yum update” to get yum to work.

  2. Hi
    I tried this but at the step:
    sudo mount centos.5-3.x86-64.img image -o loop,ro
    I am getting an error:
    ioctl : LOOP_SET_FD: Invalid argument

    Any idea about why this should happen?

  3. yeah i am with you on the following of ubuntu. i too an a RHEL man, well not really, cant afford RHEL, but its knock-off CentOS. so i am struggling trying to find something to help me along.

    found your article. though i believe we would launch with CentOS 6.x, are there any images available that you are aware of?

  4. Did someone make an el6 image yet? If not, I can probably get one up pretty quickly. Send a reply here or mark at tpsit dot.com.

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