Cloud Image Management on Eucalyptus: Creating a CentOS 6.6 EMI With ZFS Support

ZFS is a filesystem designed by Sun Microsystems that focuses on data integrity.  What makes this such an attractive filesystem to use in the cloud is that a cloud user can easily do the following:

  • set up an LVM + RAID filesystem for storing large amounts of data (e.g. database information)
  • expand the filesystem by adding more storage (i.e. EBS volumes)
  • backup the filesystem without taking the filesystem offline/unmounting
  • restore the filesystem

This blog entry will focus on how a cloud user can create their own Eucalyptus Machine Image (EMI) that has ZFS support.  The CentOS 6.5 EMI on the Eucalyptus Machine Image Catalog will be used as the base image.

Before Starting…

Before following the steps in this blog, make sure the following is in place:

Once these requirements have been met, everything should be ready to go.

Set Up Base Image/Instance

To begin, follow the ‘Quick Start’ instructions mentioned on the Eucalyptus Machine Image Catalog page.  This will install all the images provided by the catalog.  When the process has finished, list the CentOS 6.5 EMI.  For example:

# euca-describe-images emi-bdcec010 
IMAGE emi-bdcec010 centos-6.5-x86_64-20140917/centos.raw.manifest.xml 094999295155 available public x86_64 machine instance-store hvm

Once the CentOS 6.5 EMI has been listed, launch an instance from the EMI.  For example:

# euca-run-instances -k account2-user11 -t m1.medium emi-bdcec010 
RESERVATION r-a22f0201 325271821652 default
INSTANCE i-b9fccf9f emi-bdcec010 pending account2-user11 0 m1.medium 2014-12-03T22:52:41.522Z Honest monitoring-disabled instance-store hvm sg-6ef9907f x86_64
# euca-describe-instances i-b9fccf9f
RESERVATION r-a22f0201 325271821652 default
INSTANCE i-b9fccf9f emi-bdcec010 euca-172-17-248-178.future.internal running account2-user11 0 m1.medium 2014-12-03T22:52:41.522Z Honest monitoring-disabled instance-store hvm sg-6ef9907f x86_64

Once the instance is running, its ready to be customized.

Adding ZFS Support to the Instance

Now that the instance is running, SSH into the instance so the following ZFS repository can be added:

[root@odc-f-13 ~]# ssh -i account2-user11.priv
[root@euca-172-17-248-178 ~]# yum localinstall --nogpgcheck
[root@euca-172-17-248-178 ~]# yum localinstall --nogpgcheck
[root@euca-172-17-248-178 ~]# yum upgrade -y
[root@euca-172-17-248-178 ~]# yum install kernel-devel zfs -y

After all the packages have been installed, reboot the instance:

[root@euca-172-17-248-178 ~]# reboot

Preparing the Instance For EMI Creation

After rebooting the instance, SSH back into the instance and prepare the instance for EMI creation.  First, load the zfs module:

[root@odc-f-13 ~]# ssh -i account2-user11.priv
[root@euca-172-17-248-178 ~]# modprobe zfs
[root@euca-172-17-248-178 ~]# lsmod | grep zfs
zfs 1195522 0
zcommon 46278 1 zfs
znvpair 80974 2 zfs,zcommon
zavl 6925 1 zfs
zunicode 323159 1 zfs
spl 266655 5 zfs,zcommon,znvpair,zavl,zunicode

After confirming that the ZFS module is loaded, clear the network udev rules, and confirm PERSISTENT_DHCLIENT is set to “yes” in the /etc/sysconfig/network-scripts/ifcfg-eth0 file:

[root@euca-172-17-248-178 ~]# echo "" > /etc/udev/rules.d/70-persistent-net.rules
[root@euca-172-17-248-178 ~]# echo "" > /lib/udev/rules.d/75-persistent-net-generator.rules
[root@euca-172-17-248-178 ~]# echo "PERSISTENT_DHCLIENT=yes" >> /etc/sysconfig/network-scripts/ifcfg-eth0

Confirm that the instance has been upgraded to CentOS 6.6, then exit the instance.

[root@euca-172-17-248-178 ~]# cat /etc/redhat-release
CentOS release 6.6 (Final)
[root@euca-172-17-248-178 ~]# exit

Create the CentOS 6.6 EMI with ZFS Support

The instance is now ready to be bundled.  Bundle the instance using the euca-bundle-instance command.  This command is used to bundle Windows instances, however Eucalyptus extended this command to work with Linux instances as well.  Use euca-describe-bundle-tasks to monitor the bundling status:

[root@odc-f-13 ~]# euca-bundle-instance --bucket centos6.6-zfs --prefix centos6.6-zfs i-b9fccf9f
BUNDLE bun-b9fccf9f i-b9fccf9f centos6.6-zfs centos6.6-zfs 2014-12-03T23:54:51.644Z 2014-12-03T23:54:51.644Z pending 0 centos6.6-zfs/centos6.6-zfs.manifest.xml
[root@odc-f-13 ~]# euca-describe-bundle-tasks
BUNDLE bun-b9fccf9f i-b9fccf9f centos6.6-zfs centos6.6-zfs 2014-12-03T23:54:51.644Z 2014-12-03T23:57:37.517Z complete 0 centos6.6-zfs/centos6.6-zfs.manifest.xml

Once the bundle task completes, register the instance store-backed HVM image using the euca-register command:

[root@odc-f-13 ~]# euca-register -a x86_64 -n centos6.6-zfs centos6.6-zfs/centos6.6-zfs.manifest.xml --virtualization-type hvm 
IMAGE emi-5e63f02c

The custom image has been registered. Now lets test it out.

ZFS Test

To test the image out, we will do the following:

  • Launch an instance from the new EMI
  • Create 5 volumes and attach them to the instance
  • Create a ZFS storage pool and dataset

To launch the instance, use the euca-run-instances command.  To create the 5 EBS volumes, use euca-create-volume command.  After the volumes are created, use euca-attach-volume to attach the volumes to the instance.  Once the volumes are attached, the output of euca-describe-instances should look similar to the following:

# euca-describe-instances i-0cd3b6b8
RESERVATION r-cf7c5c73 325271821652 default
INSTANCE i-0cd3b6b8 emi-5e63f02c euca-172-17-248-184.future.internal running account2-user11 0 m1.medium 2014-12-04T00:16:52.887Z Honest monitoring-disabled instance-store hvm sg-6ef9907f x86_64
BLOCKDEVICE /dev/sdd vol-a23cfb1f 2014-12-04T01:45:59.730Z false
BLOCKDEVICE /dev/sdh vol-a27b75a5 2014-12-04T01:47:31.162Z false
BLOCKDEVICE /dev/sdf vol-2a971204 2014-12-04T01:46:54.575Z false
BLOCKDEVICE /dev/sdg vol-b33e9890 2014-12-04T01:47:13.346Z false
BLOCKDEVICE /dev/sde vol-dcc8b6ac 2014-12-04T01:46:15.011Z false

SSH into the instance and check what block devices are associated with the EBS volumes using the lsblk command:

# ssh -i account2-user11.priv
[root@euca-172-17-248-184 ~]# lsblk
vda 252:0 0 4.9G 0 disk
├─vda1 252:1 0 500M 0 part /boot
└─vda2 252:2 0 4.4G 0 part
 ├─VolGroup-lv_root (dm-0) 253:0 0 3.9G 0 lvm /
 └─VolGroup-lv_swap (dm-1) 253:1 0 500M 0 lvm [SWAP]
vdb 252:16 0 5.1G 0 disk
vdc 252:32 0 5G 0 disk
vdd 252:48 0 5G 0 disk
vde 252:64 0 5G 0 disk
vdf 252:80 0 5G 0 disk
vdg 252:96 0 5G 0 disk

The EBS volumes are /dev/vdc, /dev/vdd, /dev/vde, /dev/vdf, and /dev/vdg.  Use these devices to create the ZFS storage pool by using the zpool command:

[root@euca-172-17-248-184 ~]# zpool create -f app-pool vdc vdd vde vdf vdg
[root@euca-172-17-248-184 ~]# zpool status
 pool: app-pool
 state: ONLINE
 scan: none requested
 app-pool ONLINE 0 0 0
 vdc1 ONLINE 0 0 0
 vdd1 ONLINE 0 0 0
 vde1 ONLINE 0 0 0
 vdf1 ONLINE 0 0 0
 vdg1 ONLINE 0 0 0
errors: No known data errors

Next, we need to create a ZFS dataset.  For this example, this instance will end up being a MySQL server, so we will create a dataset for storing the MySQL data.

[root@euca-172-17-248-184 ~]# zfs create app-pool/mysql
[root@euca-172-17-248-184 ~]# zfs list
app-pool 152K 24.5G 30K /app-pool
app-pool/mysql 30K 24.5G 30K /app-pool/mysql

The mount point of the dataset can be adjusted by setting the mountpoint option:

[root@euca-172-17-248-184 ~]# zfs set mountpoint=/opt/mysql app-pool/mysql
[root@euca-172-17-248-184 ~]# zfs list
app-pool 162K 24.5G 31K /app-pool
app-pool/mysql 30K 24.5G 30K /opt/mysql

Thats it!  Notice how this only required 2 commands to set up a LVM + RAID filesystem, compared to around 7 commands using mdadm, pvcreate, vgcreate, mkfs, mkdir and mount. The instance is now ready to utilize the ZFS filesystem for the MySQL server.

Online Backup Example to OSG Bucket using s3cmd

As mentioned earlier, a slick feature of using ZFS is being able to perform backups online.  This section will show the following:

  • Setup and configure s3cmd
  • Create a ZFS snapshot, and use ZFS send with s3cmd to place the snapshot on an OSG bucket

To get started, in the instance, install the following packages:

[root@euca-172-17-248-184 ~]# yum install -y git python-dateutil.noarch xz

Next, clone the s3tools/s3cmd repository from Github:

[root@euca-172-17-248-184 ~]# git clone

If the instance was launched with an instance profile that assumes a role with OSG (S3) API access, s3cmd will pick up the temporary credentials and token through the Eucalyptus instance metadata service, as if the instance was launched on AWS EC2.  This wasn’t the case here, so we need to provide the Access Key ID and Secret Key manually:

[root@euca-172-17-248-184 ~]# ./s3cmd/s3cmd --configure

Enter new values or accept defaults in brackets with Enter.
Refer to user manual for detailed description of all options.

Access key and Secret key are your identifiers for Amazon S3. Leave them empty for using the env variables.
Secret Key: GMdrL97AqcybhfyyxOpNmVUnBtiMenag3ju82L7L

Encryption password is used to protect your files from reading
by unauthorized persons while in transfer to S3
Encryption password:
Path to GPG program [/usr/bin/gpg]:
When using secure HTTPS protocol all communication with Amazon S3
servers is protected from 3rd party eavesdropping. This method is
slower than plain HTTP and can't be used if you're behind a proxy
Use HTTPS protocol [No]:

On some networks all internet access must go through a HTTP proxy.
Try setting it here if you can't connect to S3 directly
HTTP Proxy server name:

New settings:
 Secret Key: GMdrL97AqcybhfyyxOpNmVUnBtiMenag3ju82L7L
 Encryption password:
 Path to GPG program: /usr/bin/gpg
 Use HTTPS protocol: False
 HTTP Proxy server name:
 HTTP Proxy server port: 0

Test access with supplied credentials? [Y/n] n
Save settings? [y/N] y
Configuration saved to '/root/.s3cfg'

Edit the .s3cfg file to make sure to point to the OSG on your Eucalyptus 4.0.2 cloud.  For example, change the following:

host_base =


host_base =


host_bucket = %(bucket)


host_bucket = %(bucket)

Confirm that s3cmd is configured correctly.  For example:

[root@euca-172-17-248-184 ~]# ./s3cmd/s3cmd ls
2014-11-05 21:45 s3://centos-images
2014-12-03 23:54 s3://centos6.6-zfs
2014-10-08 01:50 s3://instance-profile-testing
2014-12-01 22:27 s3://mongodb-snapshots
2014-10-10 20:01 s3://new-ubuntu-bundled-image
2014-09-17 18:31 s3://s3cmd-testing
2014-09-30 01:58 s3://ubuntu-bundled-vol
2014-10-22 14:47 s3://ubuntu-docker-template
2014-10-08 13:39 s3://ubuntu-images
2014-10-02 01:42 s3://ubuntu-trusty-imported-20141001
2014-10-30 18:25 s3://ubuntu-trusty-imported-20141030
2014-10-29 02:18 s3://ubuntu-trusty-server-10282014
2014-10-01 00:28 s3://wrong-s3-url-test

To perform a ZFS snapshot of the app-pool/mysql dataset, do the following:

[root@euca-172-17-248-184 ~]# zfs snapshot app-pool/mysql@wednesday
[root@euca-172-17-248-184 ~]# zfs list -t snapshot
app-pool/mysql@wednesday 0 - 30K -

After creating a bucket for the backup, send the ZFS snapshot to the bucket:

[root@euca-172-17-248-184 ~]# ./s3cmd/s3cmd mb s3://mysql-backups
[root@euca-172-17-248-184 ~]# zfs send app-pool/mysql@wednesday | xz | ./s3cmd/s3cmd put - s3://mysql-backups/mysql-backup-wednesday.img.xz
<stdin> -> s3://mysql-backups/mysql-backup-wednesday.img.xz [part 1, 1440B]
 1440 of 1440 100% in 2s 561.67 B/s done

To confirm if the snapshot is located in the bucket, use s3cmd:

[root@euca-172-17-248-184 ~]# ./s3cmd/s3cmd ls s3://mysql-backups
2014-12-04 02:22 1440 s3://mysql-backups/mysql-backup-wednesday.img.xz

Thats all folks.  We have successfully created a CentOS 6.6 EMI with ZFS support.  For more information regarding ZFS (and inspirations for this blog), check out the following resources:

Cloud Image Management on Eucalyptus: Creating a CentOS 6.6 EMI With ZFS Support