Multi Store Support¶
Note
The Multi Store feature was introduced as EXPERIMENTAL in Rocky and is now fully supported in the Train release.
Scope of this document¶
This page describes how to enable multiple stores in glance.
Prerequisites¶
Glance version 17.0.0 or Later
Glance Store Library 0.25.0 or Later
Glance not using the Glance Registry
Available backends
Procedure¶
In this section, we discuss what configuration options are available to operators to enable multiple stores support.
in the
[DEFAULT]
options group:enabled_backends
must be set as a key:value pair where key represents the identifier for the store and value will be the type of the store. Valid values are one offile
,http
,rbd
,swift
,cinder
orvmware
. In order to have multiple stores operator can specify multiple key:value separated by comma.Warning
The store identifier prefix
os_glance_
is reserved. If you define a store identifier with this prefix, the glance service will refuse to start.The http store type is always treated by Glance as a read-only store. This is indicated in the response to the
/v2/stores/info
call, where an http type store will have the attributeread-only: True
in addition to the usualid
anddescription
fields.[DEFAULT] enabled_backends = fast:rbd, cheap:rbd, shared:file, reliable:file
in the
[glance_store]
options group:default_backend
must be set to one of the identifier which are defined usingenabled_backends
option. Ifdefault_backend
is not set or if it is not representing one of the valid store drivers then it will prevent glance api service from starting.[glance_store] default_backend = fast
For each of the store identifier defined in
enabled_backends
section operator needs to add a new config group which will define config options related to that particular store.[shared] filesystem_store_datadir = /opt/stack/data/glance/shared_images/ store_description = "Shared filesystem store" [reliable] filesystem_store_datadir = /opt/stack/data/glance/reliable store_description = "Reliable filesystem backend" [fast] store_description = "Fast rbd backend" rbd_store_chunk_size = 8 rbd_store_pool = images rbd_store_user = admin rbd_store_ceph_conf = /etc/ceph/ceph.conf rados_connect_timeout = 0 [cheap] store_description = "Cheap rbd backend" rbd_store_chunk_size = 8 rbd_store_pool = images rbd_store_user = admin rbd_store_ceph_conf = /etc/ceph/ceph1.conf rados_connect_timeout = 0
Note
store_description
is a new config option added to each store where operator can add meaningful description about that store. This description is displayed in the GET /v2/info/stores response.
Store Configuration Issues¶
Please keep the following points in mind.
Due to the special read only nature and characteristics of the http store type, configuring multiple instances of the http type store is not supported. (This constraint is not currently enforced in the code.)
Each instance of the filesystem store must have a different value for the
filesystem_store_datadir
. (This constraint is not currently enforced in the code.)
Reserved Stores¶
With the Train release, Glance is beginning a transition from its former reliance upon local directories for temporary data storage to the ability to use backend stores accessed via the glance_store library.
In the Train release, the use of backend stores for this purpose is optional unless you are using the multi store support feature. Since you are reading this document, this situation most likely applies to you.
Note
Currently, only the filesystem store type is supported as a Glance reserved store.
The reserved stores are not intended to be exposed to end users. Thus
they will not appear in the response to the store discovery call, GET
/v2/info/stores, or as values in the OpenStack-image-store-ids
response header of the image-create call.
You do not get to select the name of a reserved store; these are defined
by Glance and begin with the prefix os_glance_
. In the Train release,
you do not get to select the store type: all reserved stores must be of
type filesystem.
Currently, there are two reserved stores:
os_glance_tasks_store
This store is used for the tasks engine. It replaces the use of the DEPRECATED configuration option
[task]/work_dir
.os_glance_staging_store
This store is used for the staging area for the interoperable image import process. It replaces the use of the DEPRECATED configuration option
[DEFAULT]/node_staging_uri
.
Note
If end user wants to retrieve all the available stores using
CONF.enabled_backends
then they need to remove reserved
stores from that list explicitly.
Configuration¶
As mentioned above, you do not get to select the name or the type of a reserved store (though we anticipate that you will be able configure the store type in a future release).
The reserved stores must be of type filesystem. Hence, you must
provide configuration for them in your glance-api.conf
file. You
do this by introducing a section in glance-api.conf
for each reserved
store as follows:
[os_glance_tasks_store]
filesystem_store_datadir = /var/lib/glance/tasks_work_dir
[os_glance_staging_store]
filesystem_store_datadir = /var/lib/glance/staging
Since these are both filesystem stores (remember, you do not get a choice)
the only option you must configure for each is the
filesystem_store_datadir
. Please keep the following points in mind:
The path for
filesystem_store_datadir
used for the reserved stores must be different from the path you are using for any filesystem store you have listed inenabled_backends
. Using the same data directory for multiple filesystem stores is unsupported and may lead to data loss.The identifiers for reserved stores, that is,
os_glance_tasks_store
andos_glance_staging_store
, must not be included in theenabled_backends
list.The reserved stores will not appear in the store discovery response or as values in the
OpenStack-image-store-ids
response header of the image-create call.The reserved stores will not be accepted as the value of the
X-Image-Meta-Store
header on the image-data-upload call or the image-import call.