Getting Cinder Up and Running

Lately I’ve been delving more-and-more into how Openstack handles block storage. As part of that effort, I went through the process of setting up Cinder, Openstack’s block-storage API, wiring it up to Nova, and then using it to dynamically attach a volume to a running Nova instance.

This blog entry is just a quick summary of what I learned in the process with special attention paid to a few gotchas I ran into along the way.

What is Cinder?

Cinder at its heart is an API which exposes commands to create and destroy volumes within an Openstack installation. Originally this code lived in the Nova compute service as nova-volume, but was extracted to become its own component, complete with a separate API, language bindings and its own command-line tool (cinderclient).

All this is relatively straightforward, but I think two points are worth mentioning:

First, Cinder is really just an API that happens to ship with a backend you can use out of the box. This means you could use Cinder itself for storage (using its LVM and ISCSI drivers) or you could write a Cinder compliant storage-service to suit your own needs. (If you’re already familiar with Openstack, you’ll recognize this same plugin pattern used across most projects.)

Second, Cinder does not understand compute, but compute understands Cinder. This means areas where volumes and compute intersect, like in the attaching or detaching of volumes to an instance, are the responsibility of Nova: meaning, to use Cinder with Nova, you will have to use both cinderclient to create the volume, and then novaclient to attach it.

With this in mind, let’s install and actually use Cinder, specifically:

  1. Install and configure Cinder using its LVM/ISCI backend

  2. Provision a 1 GB volume using cinderclient.

  3. Create a Nova instance and attach the volume using novaclient.

  4. Log into the instance and setup the volume to be usable space.

Installation and Configuration

For this step, we’re going to be installing Cinder from the perspective of a developer, meaning we’re going to fetch source code and run cinder directly out of the git repository.

Install Cinder

  1. Clone the repo from the Openstack repo on Github:

     $ git clone git://github.com/openstack/cinder.git
  2. Copy the base configuration into /etc/cinder:

     $ cp -R etc/cinder /etc/
    
     $ mv /etc/cinder/cinder.conf.sample /etc/cinder.conf
  3. Configure Cinder to use MySQL by adding this line to /etc/cinder/cinder.conf:

     sql_connection=mysql://root@127.0.0.1/cinder
  4. Create database and load schema:

     $ mysqladmin -uroot create cinder
     $ ./bin/cinder-manage db sync
  5. Configure LVM to manage the underlying block-storage. In my case, I’m using a second partition but you could also use a loopback device as well:

     $ apt-get install lvm2
     $ vgcreate cinder-volumes /dev/xvda2
     $ pvcreate /dev/xvda2
  6. Install tgt which will expose the block-storage over ISCSI:

     $ apt-get install tgt
  7. Configure tgt by editing /etc/tgt/targets.conf to add this line, modifying it to match the volumes directory in your cinder git repo:

     include /home/rick/Documents/code/openstack/cinder/volumes/*
  8. Start the tgt daemon. This may display some errors on startup. Those can be ignored for now:

     $ /usr/sbin/tgtd
  9. Start the cinder API and associated services:

     $ ./bin/cinder-all

Cinder now should be up and running but you still need a way to query and manage it. To do this, we’ll need to install cinderclient.

Install Cinderclient

  1. Clone python-cinderclient from the Openstack GitHub repo:

     $ git clone git://github.com/openstack/python-cinderclient.git
  2. Install it in developer-mode, this will symlink installed Python package back to your git repo:

     $ python setup.py develop
  3. Like other Openstack command-line tools, cinderclient uses environment variables for configuration, so you should create a config file and then source it, like:

     $ cat cinder.env 
     export OS_AUTH_URL=http://127.0.0.1:8776/v1/
     export OS_USERNAME=<YOUR_USERNAME>
     export OS_PASSWORD=<YOUR_PASSWORD>
     export OS_TENANT_NAME=openstack
    
     $ . cinder.env
  4. Now you can test that it works by running:

     $ cinder list  # <- should be emty since don't have any volumes yet

Configuring Nova to talk to Cinder

In order to attach volumes created with Cinder, Nova needs to know where the Cinder endpoint resides. To keep it simple, I’m not using Keystone (Openstack’s Identity Service), and instead hard-coding the endpoint with the cinder_endpoint_template configuration:

  1. Add the following to your nova.conf:

     volume_api_class=nova.volume.cinder.API
     cinder_endpoint_template=http://localhost:8776/v1/%(project_id)s
  2. Restart nova-api and nova-compute

Provision a 1 GB Volume

With Cinder, Cinderclient and Nova configured, we can now create, attach and use volumes.

  1. Create a 1GB volume

     $ cinder create --display_name cindervol 1
  2. Check to see that it exists:

     $ cinder list
     +--------------------------------------+-----------+-----------------+------+-------------+----------+-------------+
     |                  ID                  |   Status  |   Display Name  | Size | Volume Type | Bootable | Attached to |
     +--------------------------------------+-----------+-----------------+------+-------------+----------+-------------+
     | da6ae608-4673-4b24-acd4-75e527b5969a | available |    cindervol    |  1   |     None    |  false   |             |
     +--------------------------------------+-----------+-----------------+------+-------------+----------+-------------+

Attach Volume to Instance

  1. Create the instance using whatever image and flavor combo you want:

     $ nova create --image <YOUR IMAGE> --flavor 1 myinstance
  2. Attach the volume to the running instance.

    You’ll need to specify a device identifier within your instance that isn’t being used. In my case, I know that /dev/xvdc is being used for swap but that /dev/xvdb is free, so I’ll use that:

      $ nova volume-attach myinstance da6ae608-4673-4b24-acd4-75e527b5969a /dev/xvdb

Use the Attached Volume

Now that the volume has been attached, you need to perform some setup within the instance so that you can actually use it.

  1. First, login to your instance

     $ ssh myinstance
  2. Next, ensure that the device for new volume is present:

     $ ls /dev/xvdb
     /dev/xvdb
  3. Assuming it’s present, you can now format it:

     $ mkfs /dev/xvdb
  4. Mount the newly formatted disk

     $ mkdir /cindervol
     $ mount /dev/xvdb /cindervol
  5. Finally, verify that the newly mounted volume has the correct size.

     $ df -h
     Filesystem            Size  Used Avail Use% Mounted on
     /dev/xvda1             12G  738M   11G   7% /
     tmpfs                  28M     0   28M   0% /lib/init/rw
     udev                   15M   44K   15M   1% /dev
     tmpfs                  28M     0   28M   0% /dev/shm
     /dev/xvdb            1008M  1.3M  956M   1% /cindervol

We can see from the output, the Cinder-created volume has the correct size so the process has worked end-to-end.

Further Reading

The minimal Cinder setup we just created is great for learning the code and see how things fit together but, as you become more familiar with it, you’re probably going to want to expand to a more complex setup to take advantage of advanced features, for example Keystone integration. Your two best bets here are diving into the code itself (daunting at first, but print/raise statements are your friend) and checking out the online documentation.

Posted on 14 January 2013.
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