RBD: Implement v2.1 replication

[OpenStack Infra]

https://review.openstack.org/333565
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commit f81d8a37debce61b9f5414257419af87bfce536d
Author: Jon Bernard <email address hidden>
Date: Thu Aug 4 14:41:44 2016 -0400

    RBD: Implement v2.1 replication

    This patch implements v2.1 replication in the RBD driver. A single ceph
    backend can support both replicated and non-replicated volumes using
    volume types. For replicated volumes, both clusters are expected to be
    configured with rbd-mirror with keys in place and image mirroring
    enabled on the pool. The RBD driver will enable replication per-volume
    if the volume type requests it.

    On failover, each replicated volume is promoted to primary on the
    secondary cluster and new connection requests will receive connection
    information for the volume on the secondary cluster. At the time of
    writing, failback is not supported by Cinder and requires admin
    intervention to reach a per-failover state.

    Non replicated volumes will be set to error status to reflect that they
    are not available, and the previous status will be stored in the
    replication_driver_data field.

    There are two configuration pieces required to make this work:

    1. A volume type that enables replication:

        $ cinder type-create replicated
        $ cinder type-key replicated set volume_backend_name=ceph
        $ cinder type-key replicated set replication_enabled='<is> True'

    2. A secondary backend defined in cinder.conf:

        [ceph]
        ...
        replication_device = backend_id:secondary,
                             conf:/etc/ceph/secondary.conf,
                             user:cinder

    The only required parameter is backend_id, as conf and user have
    defaults. Conf defaults to /etc/ceph/$backend_id.conf and user defaults
    to rbd_user or cinder if that one is None.

    We also have a new configuration option for the RBD driver called
    replication_connect_timeout that allows us to specify the timeout for
    the promotion/demotion of a single volume.

    We try to do a clean failover for cases where there is still
    connectivity with the primary cluster, so we'll try to do a demotion of
    the original images, and when one of the demotions fails we just assume
    that all of the other demotions will fail as well (the cluster is not
    accesible) so we'll do a forceful promotion for those images.

    DocImpact
    Implements: blueprint rbd-replication
    Co-Authored-By: Gorka Eguileor <email address hidden>
    Change-Id: I58c38fe11014aaade6b42f4bdf9d32b73c82e18d

[Sofia Enriquez (lsofia-enriquez)]

As far as I can see we already have the documentation: https://docs.openstack.org/cinder/latest/contributor/replication.html

I'm going to close this.