Collocating Ceph volumes and instances in a multi-datacenter setup

OpenStack Havana is installed on machines rented from OVH and Hetzner. An aggregate is created for machines hosted at OVH and another for machines hosted at Hetzner. A Ceph cluster is created with a pool using disks from OVH and another pool using disks from Hetzner. A cinder backend is created for each Ceph pool. From the dashboard, an instance can be created in the OVH availability zone using a Ceph volume provided by the matching OVH pool.

Creating availability zones

The availability zones are created as a side effect of creating an aggregate.

# nova aggregate-create ovh ovh
+----+------+-------------------+-------+--------------------------------+
| Id | Name | Availability Zone | Hosts | Metadata                       |
+----+------+-------------------+-------+--------------------------------+
| 2  | ovh  | ovh               | []    | {u'availability_zone': u'ovh'} |
+----+------+-------------------+-------+--------------------------------+
# nova aggregate-create hetzner hetzner
+----+---------+-------------------+-------+------------------------------------+
| Id | Name    | Availability Zone | Hosts | Metadata                           |
+----+---------+-------------------+-------+------------------------------------+
| 3  | hetzner | hetzner           | []    | {u'availability_zone': u'hetzner'} |
+----+---------+-------------------+-------+------------------------------------+

The hosts are assigned to their availability zone:

# nova aggregate-add-host ovh bm0015.the.re
Aggregate 2 has been successfully updated.
+----+------+-------------------+--------------------+--------------------------------+
| Id | Name | Availability Zone | Hosts              | Metadata                       |
+----+------+-------------------+--------------------+--------------------------------+
| 2  | ovh  | ovh               | [u'bm0015.the.re'] | {u'availability_zone': u'ovh'} |
+----+------+-------------------+--------------------+--------------------------------+

The result can be checked with

# nova availability-zone-list
+-----------------------+----------------------------------------+
| Name                  | Status                                 |
+-----------------------+----------------------------------------+
| internal              | available                              |
| |- bm0015.the.re      |                                        |
| | |- nova-conductor   | enabled :-)  2013-11-11T14:26:43.000000 |
| | |- nova-consoleauth | enabled :-)  2013-11-11T14:26:43.000000 |
| | |- nova-scheduler   | enabled :-)  2013-11-11T14:26:43.000000 |
| | |- nova-cert        | enabled :-)  2013-11-11T14:26:43.000000 |
| ovh                   | available                              |
| |- bm0015.the.re      |                                        |
| | |- nova-compute     | enabled :-)  2013-11-11T14:26:48.000000 |
| hetzner               | available                              |
| |- bm0016.the.re      |                                        |
| | |- nova-compute     | enabled :-)  2013-11-11T14:26:49.000000 |
| nova                  | available                              |
+-----------------------+----------------------------------------+

Creating the Ceph pools

The crush map is extracted with

ceph osd getcrushmap -o crush.bin
crushtool -d crush.bin -o crush.txt

It is edited to add

datacenter ovh {
        id -5
        alg straw
        hash 0
        item bm0014 weight 1.820
        item bm0015 weight 1.820
}

rule ovh {
        ruleset 3
        type replicated
        min_size 1
        max_size 10
        step take ovh
        step chooseleaf firstn 0 type host
        step emit
}

and sent back to the Ceph monitors with

crushtool -c crush.txt -o crush.bin
ceph osd setcrushmap crush.bin

An ovh pool is created and set to use the ovh ruleset:

ceph osd pool create ovh 128
ceph osd pool set ovh crush_ruleset 3

The crush.txt file also contains the ruleset for the hetzner pool.

Creating cinder backends

In the /etc/cinder/cinder.conf file of the host running cinder-volume, one cinder backend is defined for each Ceph pool:

enabled_backends=rbd-hetzner,rbd-ovh
[rbd-hetzner]
volume_driver=cinder.volume.driver.RBDDriver
rbd_pool=hetzner
volume_backend_name=RBD_HETZNER
[rbd-ovh]
volume_driver=cinder.volume.driver.RBDDriver
rbd_pool=ovh
volume_backend_name=RBD_OVH

In order to enable the –volume-type ovh option of cinder create, the corresponding type keys must be created:

# cinder type-create ovh
+--------------------------------------+------+
|                  ID                  | Name |
+--------------------------------------+------+
| 48645332-4835-4a9b-9078-cd735f47dae5 | ovh  |
+--------------------------------------+------+
# cinder type-key ovh set volume_backend_name=RBD_OVH
# cinder extra-specs-list
+--------------------------------------+---------+------------------------------------------+
|                  ID                  |   Name  |               extra_specs                |
+--------------------------------------+---------+------------------------------------------+
| 48645332-4835-4a9b-9078-cd735f47dae5 |   ovh   |   {u'volume_backend_name': u'RBD_OVH'}   |
+--------------------------------------+---------+------------------------------------------+

Check that the cinder scheduler is set as follows in /etc/cinder/cinder.conf

scheduler_driver=cinder.scheduler.filter_scheduler.FilterScheduler

Assembling instance and volume

After creating a volume using the OVH cinder backend:

cinder create --volume-type ovh --display-name test 1

An instance is created in the OVH availability zone:

nova boot --availability-zone ovh \
               --image 'cirros image' \
               --key-name key_loic \
               --nic net-id=e1d72366-1f25-42c1-a953-a944c9f932e3 \
               --flavor m1.tiny --poll try

The volume is attached to the instance

nova volume-attach try 045d1cae-cd9b-4d64-b0b8-544f5b6d0c5a /dev/vdb
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