![Gorka Eguileor](/assets/img/avatar_default.png)
Currently our code and contributor documentation doesn't mention the difference between the two different UUIDs we can have and how drivers should use them. This patch tries to provide a brief description about it in multiple places to reduce the number of bugs that happen around it. Change-Id: I946ead7547571ccd1b2df55ac1f3d4689d1f8089
9.4 KiB
Drivers
Cinder exposes an API to users to interact with different storage backend solutions. The following are standards across all drivers for Cinder services to properly interact with a driver.
Basic attributes
There are some basic attributes that all drivers classes should have:
- VERSION: Driver version in string format. No naming convention is imposed, although semantic versioning is recommended.
- CI_WIKI_NAME: Must be the exact name of the ThirdPartySystems wiki page. This is used by our tooling system to associate jobs to drivers and track their CI reporting status correctly.
The tooling system will also use the name and docstring of the driver class.
Configuration options
Each driver requires different configuration options set in the cinder.conf file to operate, and due to the complexities of the Object Oriented programming mechanisms (inheritance, composition, overwriting, etc.) once your driver defines its parameters in the code Cinder has no automated way of telling which configuration options are relevant to your driver.
In order to assist operators and installation tools we recommend reporting the relevant options:
- For operators: In the documentation under
doc/source/configuration/block-storage
. - For operators and installers: Through the
get_driver_options
static method returning that returns a list of all the Oslo Config parameters.
Minimum Features
Minimum features are enforced to avoid having a grid of what features are supported by which drivers and which releases. Cinder Core requires that all drivers implement the following minimum features.
Core Functionality
- Volume Create/Delete
- Volume Attach/Detach
- Snapshot Create/Delete
- Create Volume from Snapshot
- Get Volume Stats
- Copy Image to Volume
- Copy Volume to Image
- Clone Volume
- Extend Volume
Security Requirements
- Drivers must delete volumes in a way where volumes deleted from the backend will not leak data into new volumes when they are created. Cinder operates in multi-tenant environments and this is critical to ensure data safety.
- Drivers should support secure TLS/SSL communication between the cinder volume service and the backend as configured by the "driver_ssl_cert_verify" and "driver_ssl_cert_path" options in cinder.conf.
- Drivers should use standard Python libraries to handle encryption-related functionality, and not contain custom implementations of encryption code.
Volume Stats
Volume stats are used by the different schedulers for the drivers to provide a report on their current state of the backend. The following should be provided by a driver.
- driver_version
- free_capacity_gb
- storage_protocol
- total_capacity_gb
- vendor_name
- volume_backend_name
NOTE: If the driver is unable to provide a value for free_capacity_gb or total_capacity_gb, keywords can be provided instead. Please use 'unknown' if the backend cannot report the value or 'infinite' if the backend has no upper limit. But, it is recommended to report real values as the Cinder scheduler assigns lowest weight to any storage backend reporting 'unknown' or 'infinite'.
NOTE: By default, Cinder assumes that the driver supports attached volume extending. If it doesn't, it should report 'online_extend_support=False'. Otherwise the scheduler will attempt to perform the operation, and may leave the volume in 'error_extending' state.
Value of storage_protocol
is a single string
representing the transport protocol used by the storage. Existing
protocols are present in cinder.common.constants
and should
be used by drivers instead of string literals.
Variant values only exist for older drivers that were already reporting those values. New drivers must use non variant versions.
The storage_protocol
can be used by operators using the
cinder get-pools --detail
command, by volume types in their
extra specs, and by the filter and goodness functions.
We must not mistake the value of the storage_protocol
with the identifier of the os-brick connector, which is returned by the
initialize_connection
driver method in the
driver_volume_type
dictionary key. In some cases they may
have the same value, but they are different things.
Feature Enforcement
All concrete driver implementations should use the
cinder.interface.volumedriver
decorator on the driver
class:
@interface.volumedriver
class LVMVolumeDriver(driver.VolumeDriver):
This will register the driver and allow automated compliance tests to run against and verify the compliance of the driver against the required interface to support the Core Functionality listed above.
Running tox -e compliance
will verify all registered
drivers comply to this interface. This can be used during development to
perform self checks along the way. Any missing method calls will be
identified by the compliance tests.
The details for the required volume driver interfaces can be found in
the cinder/interface/volume_*_driver.py
source.
New Driver Review Checklist
There are some common issues caught during the review of new driver
patches that can easily be avoided. New driver maintainers should review
the new_driver_checklist
for some things to watch out
for.
new_driver_checklist
Driver Development Documentations
The LVM driver is our reference for all new driver implementations. The information below can provide additional documentation for the methods that volume drivers need to implement.
Volume ID
Drivers should always get a volume's ID using the
name_id
attribute instead of the id
attribute.
A Cinder volume may have two different UUIDs, a user facing one, and one the driver should use.
When a volume is created these two are the same, but when doing a generic migration (create new volume, then copying data) they will be different if we were unable to rename the new volume in the final migration steps.
So the volume will have been created using the new volume's UUID and the driver will have to look for it using that UUID, but the user on the other hand will keep referencing the volume with the original UUID.
Base Driver Interface
The methods documented below are the minimum required interface for a volume driver to support. All methods from this interface must be implemented in order to be an official Cinder volume driver.
cinder.interface.volume_driver
Manage/Unmanage Support
An optional feature a volume backend can support is the ability to manage existing volumes or unmanage volumes - keep the volume on the storage backend but no longer manage it through Cinder.
To support this functionality, volume drivers must implement these methods:
cinder.interface.volume_manageable_driver
Manage/Unmanage Snapshot Support
In addition to the ability to manage and unmanage volumes, Cinder backend drivers may also support managing and unmanaging volume snapshots. These additional methods must be implemented to support these operations.
cinder.interface.volume_snapshotmanagement_driver
Volume Consistency Groups
Some storage backends support the ability to group volumes and create write consistent snapshots across the group. In order to support these operations, the following interface must be implemented by the driver.
cinder.interface.volume_consistencygroup_driver
Generic Volume Groups
The generic volume groups feature provides the ability to manage a group of volumes together. Because this feature is implemented at the manager level, every driver gets this feature by default. If a driver wants to override the default behavior to support additional functionalities such as consistent group snapshot, the following interface must be implemented by the driver. Once every driver supporting volume consistency groups has added the consistent group snapshot capability to generic volume groups, we no longer need the volume consistency groups interface listed above.
cinder.interface.volume_group_driver
Revert To Snapshot
Some storage backends support the ability to revert a volume to the last snapshot. To support snapshot revert, the following interface must be implemented by the driver.
cinder.interface.volume_snapshot_revert