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diff --git a/doc/rbd/rbd-mirroring.rst b/doc/rbd/rbd-mirroring.rst new file mode 100644 index 000000000..d5d1191d6 --- /dev/null +++ b/doc/rbd/rbd-mirroring.rst @@ -0,0 +1,529 @@ +=============== + RBD Mirroring +=============== + +.. index:: Ceph Block Device; mirroring + +RBD images can be asynchronously mirrored between two Ceph clusters. This +capability is available in two modes: + +* **Journal-based**: This mode uses the RBD journaling image feature to ensure + point-in-time, crash-consistent replication between clusters. Every write to + the RBD image is first recorded to the associated journal before modifying the + actual image. The remote cluster will read from this associated journal and + replay the updates to its local copy of the image. Since each write to the + RBD image will result in two writes to the Ceph cluster, expect write + latencies to nearly double while using the RBD journaling image feature. + +* **Snapshot-based**: This mode uses periodically scheduled or manually + created RBD image mirror-snapshots to replicate crash-consistent RBD images + between clusters. The remote cluster will determine any data or metadata + updates between two mirror-snapshots and copy the deltas to its local copy of + the image. With the help of the RBD ``fast-diff`` image feature, updated data + blocks can be quickly determined without the need to scan the full RBD image. + Since this mode is not as fine-grained as journaling, the complete delta + between two snapshots will need to be synced prior to use during a failover + scenario. Any partially applied set of deltas will be rolled back at moment + of failover. + +.. note:: journal-based mirroring requires the Ceph Jewel release or later; + snapshot-based mirroring requires the Ceph Octopus release or later. + +Mirroring is configured on a per-pool basis within peer clusters and can be +configured on a specific subset of images within the pool. You can also mirror +all images within a given pool when using journal-based +mirroring. Mirroring is configured using the ``rbd`` command. The +``rbd-mirror`` daemon is responsible for pulling image updates from the remote +peer cluster and applying them to the image within the local cluster. + +Depending on the desired needs for replication, RBD mirroring can be configured +for either one- or two-way replication: + +* **One-way Replication**: When data is only mirrored from a primary cluster to + a secondary cluster, the ``rbd-mirror`` daemon runs only on the secondary + cluster. + +* **Two-way Replication**: When data is mirrored from primary images on one + cluster to non-primary images on another cluster (and vice-versa), the + ``rbd-mirror`` daemon runs on both clusters. + +.. important:: Each instance of the ``rbd-mirror`` daemon must be able to + connect to both the local and remote Ceph clusters simultaneously (i.e. + all monitor and OSD hosts). Additionally, the network must have sufficient + bandwidth between the two data centers to handle mirroring workload. + +Pool Configuration +================== + +The following procedures demonstrate how to perform the basic administrative +tasks to configure mirroring using the ``rbd`` command. Mirroring is +configured on a per-pool basis. + +These pool configuration steps should be performed on both peer clusters. These +procedures assume that both clusters, named "site-a" and "site-b", are accessible +from a single host for clarity. + +See the `rbd`_ manpage for additional details of how to connect to different +Ceph clusters. + +.. note:: The cluster name in the following examples corresponds to a Ceph + configuration file of the same name (e.g. /etc/ceph/site-b.conf). See the + `ceph-conf`_ documentation for how to configure multiple clusters. Note + that ``rbd-mirror`` does **not** require the source and destination clusters + to have unique internal names; both can and should call themselves ``ceph``. + The config `files` that ``rbd-mirror`` needs for local and remote clusters + can be named arbitrarily, and containerizing the daemon is one strategy + for maintaining them outside of ``/etc/ceph`` to avoid confusion. + +Enable Mirroring +---------------- + +To enable mirroring on a pool with ``rbd``, issue the ``mirror pool enable`` +subcommand with the pool name, and the mirroring mode:: + + rbd mirror pool enable {pool-name} {mode} + +The mirroring mode can either be ``image`` or ``pool``: + +* **image**: When configured in ``image`` mode, mirroring must + `explicitly enabled`_ on each image. +* **pool** (default): When configured in ``pool`` mode, all images in the pool + with the journaling feature enabled are mirrored. + +For example:: + + $ rbd --cluster site-a mirror pool enable image-pool image + $ rbd --cluster site-b mirror pool enable image-pool image + +Disable Mirroring +----------------- + +To disable mirroring on a pool with ``rbd``, specify the ``mirror pool disable`` +command and the pool name:: + + rbd mirror pool disable {pool-name} + +When mirroring is disabled on a pool in this way, mirroring will also be +disabled on any images (within the pool) for which mirroring was enabled +explicitly. + +For example:: + + $ rbd --cluster site-a mirror pool disable image-pool + $ rbd --cluster site-b mirror pool disable image-pool + +Bootstrap Peers +--------------- + +In order for the ``rbd-mirror`` daemon to discover its peer cluster, the peer +must be registered and a user account must be created. +This process can be automated with ``rbd`` and the +``mirror pool peer bootstrap create`` and ``mirror pool peer bootstrap import`` +commands. + +To manually create a new bootstrap token with ``rbd``, issue the +``mirror pool peer bootstrap create`` subcommand, a pool name, and an +optional friendly site name to describe the local cluster:: + + rbd mirror pool peer bootstrap create [--site-name {local-site-name}] {pool-name} + +The output of ``mirror pool peer bootstrap create`` will be a token that should +be provided to the ``mirror pool peer bootstrap import`` command. For example, +on site-a:: + + $ rbd --cluster site-a mirror pool peer bootstrap create --site-name site-a image-pool + eyJmc2lkIjoiOWY1MjgyZGItYjg5OS00NTk2LTgwOTgtMzIwYzFmYzM5NmYzIiwiY2xpZW50X2lkIjoicmJkLW1pcnJvci1wZWVyIiwia2V5IjoiQVFBUnczOWQwdkhvQmhBQVlMM1I4RmR5dHNJQU50bkFTZ0lOTVE9PSIsIm1vbl9ob3N0IjoiW3YyOjE5Mi4xNjguMS4zOjY4MjAsdjE6MTkyLjE2OC4xLjM6NjgyMV0ifQ== + +To manually import the bootstrap token created by another cluster with ``rbd``, +specify the ``mirror pool peer bootstrap import`` command, the pool name, a file +path to the created token (or '-' to read from standard input), along with an +optional friendly site name to describe the local cluster and a mirroring +direction (defaults to rx-tx for bidirectional mirroring, but can also be set +to rx-only for unidirectional mirroring):: + + rbd mirror pool peer bootstrap import [--site-name {local-site-name}] [--direction {rx-only or rx-tx}] {pool-name} {token-path} + +For example, on site-b:: + + $ cat <<EOF > token + eyJmc2lkIjoiOWY1MjgyZGItYjg5OS00NTk2LTgwOTgtMzIwYzFmYzM5NmYzIiwiY2xpZW50X2lkIjoicmJkLW1pcnJvci1wZWVyIiwia2V5IjoiQVFBUnczOWQwdkhvQmhBQVlMM1I4RmR5dHNJQU50bkFTZ0lOTVE9PSIsIm1vbl9ob3N0IjoiW3YyOjE5Mi4xNjguMS4zOjY4MjAsdjE6MTkyLjE2OC4xLjM6NjgyMV0ifQ== + EOF + $ rbd --cluster site-b mirror pool peer bootstrap import --site-name site-b image-pool token + +Add Cluster Peer Manually +------------------------- + +Cluster peers can be specified manually if desired or if the above bootstrap +commands are not available with the currently installed Ceph release. + +The remote ``rbd-mirror`` daemon will need access to the local cluster to +perform mirroring. A new local Ceph user should be created for the remote +daemon to use. To `create a Ceph user`_, with ``ceph`` specify the +``auth get-or-create`` command, user name, monitor caps, and OSD caps:: + + ceph auth get-or-create client.rbd-mirror-peer mon 'profile rbd' osd 'profile rbd' + +The resulting keyring should be copied to the other cluster's ``rbd-mirror`` +daemon hosts if not using the Ceph monitor ``config-key`` store described below. + +To manually add a mirroring peer Ceph cluster with ``rbd``, specify the +``mirror pool peer add`` command, the pool name, and a cluster specification:: + + rbd mirror pool peer add {pool-name} {client-name}@{cluster-name} + +For example:: + + $ rbd --cluster site-a mirror pool peer add image-pool client.rbd-mirror-peer@site-b + $ rbd --cluster site-b mirror pool peer add image-pool client.rbd-mirror-peer@site-a + +By default, the ``rbd-mirror`` daemon needs to have access to a Ceph +configuration file located at ``/etc/ceph/{cluster-name}.conf`` that provides +the addresses of the peer cluster's monitors, in addition to a keyring for +``{client-name}`` located in the default or configured keyring search paths +(e.g. ``/etc/ceph/{cluster-name}.{client-name}.keyring``). + +Alternatively, the peer cluster's monitor and/or client key can be securely +stored within the local Ceph monitor ``config-key`` store. To specify the +peer cluster connection attributes when adding a mirroring peer, use the +``--remote-mon-host`` and ``--remote-key-file`` optionals. For example:: + + $ cat <<EOF > remote-key-file + AQAeuZdbMMoBChAAcj++/XUxNOLFaWdtTREEsw== + EOF + $ rbd --cluster site-a mirror pool peer add image-pool client.rbd-mirror-peer@site-b --remote-mon-host 192.168.1.1,192.168.1.2 --remote-key-file remote-key-file + $ rbd --cluster site-a mirror pool info image-pool --all + Mode: pool + Peers: + UUID NAME CLIENT MON_HOST KEY + 587b08db-3d33-4f32-8af8-421e77abb081 site-b client.rbd-mirror-peer 192.168.1.1,192.168.1.2 AQAeuZdbMMoBChAAcj++/XUxNOLFaWdtTREEsw== + +Remove Cluster Peer +------------------- + +To remove a mirroring peer Ceph cluster with ``rbd``, specify the +``mirror pool peer remove`` command, the pool name, and the peer UUID +(available from the ``rbd mirror pool info`` command):: + + rbd mirror pool peer remove {pool-name} {peer-uuid} + +For example:: + + $ rbd --cluster site-a mirror pool peer remove image-pool 55672766-c02b-4729-8567-f13a66893445 + $ rbd --cluster site-b mirror pool peer remove image-pool 60c0e299-b38f-4234-91f6-eed0a367be08 + +Data Pools +---------- + +When creating images in the destination cluster, ``rbd-mirror`` selects a data +pool as follows: + +#. If the destination cluster has a default data pool configured (with the + ``rbd_default_data_pool`` configuration option), it will be used. +#. Otherwise, if the source image uses a separate data pool, and a pool with the + same name exists on the destination cluster, that pool will be used. +#. If neither of the above is true, no data pool will be set. + +Image Configuration +=================== + +Unlike pool configuration, image configuration only needs to be performed +against a single mirroring peer Ceph cluster. + +Mirrored RBD images are designated as either primary or non-primary. This is a +property of the image and not the pool. Images that are designated as +non-primary cannot be modified. + +Images are automatically promoted to primary when mirroring is first enabled on +an image (either implicitly if the pool mirror mode was ``pool`` and the image +has the journaling image feature enabled, or `explicitly enabled`_ by the +``rbd`` command if the pool mirror mode was ``image``). + +Enable Image Mirroring +---------------------- + +If mirroring is configured in ``image`` mode for the image's pool, then it +is necessary to explicitly enable mirroring for each image within the pool. +To enable mirroring for a specific image with ``rbd``, specify the +``mirror image enable`` command along with the pool, image name, and mode:: + + rbd mirror image enable {pool-name}/{image-name} {mode} + +The mirror image mode can either be ``journal`` or ``snapshot``: + +* **journal** (default): When configured in ``journal`` mode, mirroring will + utilize the RBD journaling image feature to replicate the image contents. If + the RBD journaling image feature is not yet enabled on the image, it will be + automatically enabled. + +* **snapshot**: When configured in ``snapshot`` mode, mirroring will utilize + RBD image mirror-snapshots to replicate the image contents. Once enabled, an + initial mirror-snapshot will automatically be created. Additional RBD image + `mirror-snapshots`_ can be created by the ``rbd`` command. + +For example:: + + $ rbd --cluster site-a mirror image enable image-pool/image-1 snapshot + $ rbd --cluster site-a mirror image enable image-pool/image-2 journal + +Enable Image Journaling Feature +------------------------------- + +RBD journal-based mirroring uses the RBD image journaling feature to ensure that +the replicated image always remains crash-consistent. When using the ``image`` +mirroring mode, the journaling feature will be automatically enabled when +mirroring is enabled on the image. When using the ``pool`` mirroring mode, +before an image can be mirrored to a peer cluster, the RBD image journaling +feature must be enabled. The feature can be enabled at image creation time by +providing the ``--image-feature exclusive-lock,journaling`` option to the +``rbd`` command. + +Alternatively, the journaling feature can be dynamically enabled on +pre-existing RBD images. To enable journaling with ``rbd``, specify +the ``feature enable`` command, the pool and image name, and the feature name:: + + rbd feature enable {pool-name}/{image-name} {feature-name} + +For example:: + + $ rbd --cluster site-a feature enable image-pool/image-1 journaling + +.. note:: The journaling feature is dependent on the exclusive-lock feature. If + the exclusive-lock feature is not already enabled, it should be enabled prior + to enabling the journaling feature. + +.. tip:: You can enable journaling on all new images by default by adding + ``rbd default features = 125`` to your Ceph configuration file. + +.. tip:: ``rbd-mirror`` tunables are set by default to values suitable for + mirroring an entire pool. When using ``rbd-mirror`` to migrate single + volumes been clusters you may achieve substantial performance gains + by setting ``rbd_mirror_journal_max_fetch_bytes=33554432`` and + ``rbd_journal_max_payload_bytes=8388608`` within the ``[client]`` config + section of the local or centralized configuration. Note that these + settings may allow ``rbd-mirror`` to present a substantial write workload + to the destination cluster: monitor cluster performance closely during + migrations and test carefuly before running multiple migrations in parallel. + +Create Image Mirror-Snapshots +----------------------------- + +When using snapshot-based mirroring, mirror-snapshots will need to be created +whenever it is desired to mirror the changed contents of the RBD image. To +create a mirror-snapshot manually with ``rbd``, specify the +``mirror image snapshot`` command along with the pool and image name:: + + rbd mirror image snapshot {pool-name}/{image-name} + +For example:: + + $ rbd --cluster site-a mirror image snapshot image-pool/image-1 + +By default up to ``5`` mirror-snapshots will be created per-image. The most +recent mirror-snapshot is automatically pruned if the limit is reached. +The limit can be overridden via the ``rbd_mirroring_max_mirroring_snapshots`` +configuration option if required. Additionally, mirror-snapshots are +automatically deleted when the image is removed or when mirroring is disabled. + +Mirror-snapshots can also be automatically created on a periodic basis if +mirror-snapshot schedules are defined. The mirror-snapshot can be scheduled +globally, per-pool, or per-image levels. Multiple mirror-snapshot schedules can +be defined at any level, but only the most-specific snapshot schedules that +match an individual mirrored image will run. + +To create a mirror-snapshot schedule with ``rbd``, specify the +``mirror snapshot schedule add`` command along with an optional pool or +image name; interval; and optional start time:: + + rbd mirror snapshot schedule add [--pool {pool-name}] [--image {image-name}] {interval} [{start-time}] + +The ``interval`` can be specified in days, hours, or minutes using ``d``, ``h``, +``m`` suffix respectively. The optional ``start-time`` can be specified using +the ISO 8601 time format. For example:: + + $ rbd --cluster site-a mirror snapshot schedule add --pool image-pool 24h 14:00:00-05:00 + $ rbd --cluster site-a mirror snapshot schedule add --pool image-pool --image image1 6h + +To remove a mirror-snapshot schedules with ``rbd``, specify the +``mirror snapshot schedule remove`` command with options that match the +corresponding ``add`` schedule command. + +To list all snapshot schedules for a specific level (global, pool, or image) +with ``rbd``, specify the ``mirror snapshot schedule ls`` command along with +an optional pool or image name. Additionally, the ``--recursive`` option can +be specified to list all schedules at the specified level and below. For +example:: + + $ rbd --cluster site-a mirror schedule ls --pool image-pool --recursive + POOL NAMESPACE IMAGE SCHEDULE + image-pool - - every 1d starting at 14:00:00-05:00 + image-pool image1 every 6h + +To view the status for when the next snapshots will be created for +snapshot-based mirroring RBD images with ``rbd``, specify the +``mirror snapshot schedule status`` command along with an optional pool or +image name:: + + rbd mirror snapshot schedule status [--pool {pool-name}] [--image {image-name}] + +For example:: + + $ rbd --cluster site-a mirror schedule status + SCHEDULE TIME IMAGE + 2020-02-26 18:00:00 image-pool/image1 + +Disable Image Mirroring +----------------------- + +To disable mirroring for a specific image with ``rbd``, specify the +``mirror image disable`` command along with the pool and image name:: + + rbd mirror image disable {pool-name}/{image-name} + +For example:: + + $ rbd --cluster site-a mirror image disable image-pool/image-1 + +Image Promotion and Demotion +---------------------------- + +In a failover scenario where the primary designation needs to be moved to the +image in the peer Ceph cluster, access to the primary image should be stopped +(e.g. power down the VM or remove the associated drive from a VM), demote the +current primary image, promote the new primary image, and resume access to the +image on the alternate cluster. + +.. note:: RBD only provides the necessary tools to facilitate an orderly + failover of an image. An external mechanism is required to coordinate the + full failover process (e.g. closing the image before demotion). + +To demote a specific image to non-primary with ``rbd``, specify the +``mirror image demote`` command along with the pool and image name:: + + rbd mirror image demote {pool-name}/{image-name} + +For example:: + + $ rbd --cluster site-a mirror image demote image-pool/image-1 + +To demote all primary images within a pool to non-primary with ``rbd``, specify +the ``mirror pool demote`` command along with the pool name:: + + rbd mirror pool demote {pool-name} + +For example:: + + $ rbd --cluster site-a mirror pool demote image-pool + +To promote a specific image to primary with ``rbd``, specify the +``mirror image promote`` command along with the pool and image name:: + + rbd mirror image promote [--force] {pool-name}/{image-name} + +For example:: + + $ rbd --cluster site-b mirror image promote image-pool/image-1 + +To promote all non-primary images within a pool to primary with ``rbd``, specify +the ``mirror pool promote`` command along with the pool name:: + + rbd mirror pool promote [--force] {pool-name} + +For example:: + + $ rbd --cluster site-a mirror pool promote image-pool + +.. tip:: Since the primary / non-primary status is per-image, it is possible to + have two clusters split the IO load and stage failover / failback. + +.. note:: Promotion can be forced using the ``--force`` option. Forced + promotion is needed when the demotion cannot be propagated to the peer + Ceph cluster (e.g. Ceph cluster failure, communication outage). This will + result in a split-brain scenario between the two peers and the image will no + longer be in-sync until a `force resync command`_ is issued. + +Force Image Resync +------------------ + +If a split-brain event is detected by the ``rbd-mirror`` daemon, it will not +attempt to mirror the affected image until corrected. To resume mirroring for an +image, first `demote the image`_ determined to be out-of-date and then request a +resync to the primary image. To request an image resync with ``rbd``, specify +the ``mirror image resync`` command along with the pool and image name:: + + rbd mirror image resync {pool-name}/{image-name} + +For example:: + + $ rbd mirror image resync image-pool/image-1 + +.. note:: The ``rbd`` command only flags the image as requiring a resync. The + local cluster's ``rbd-mirror`` daemon process is responsible for performing + the resync asynchronously. + +Mirror Status +============= + +The peer cluster replication status is stored for every primary mirrored image. +This status can be retrieved using the ``mirror image status`` and +``mirror pool status`` commands. + +To request the mirror image status with ``rbd``, specify the +``mirror image status`` command along with the pool and image name:: + + rbd mirror image status {pool-name}/{image-name} + +For example:: + + $ rbd mirror image status image-pool/image-1 + +To request the mirror pool summary status with ``rbd``, specify the +``mirror pool status`` command along with the pool name:: + + rbd mirror pool status {pool-name} + +For example:: + + $ rbd mirror pool status image-pool + +.. note:: Adding ``--verbose`` option to the ``mirror pool status`` command will + additionally output status details for every mirroring image in the pool. + +rbd-mirror Daemon +================= + +The two ``rbd-mirror`` daemons are responsible for watching image journals on +the remote, peer cluster and replaying the journal events against the local +cluster. The RBD image journaling feature records all modifications to the +image in the order they occur. This ensures that a crash-consistent mirror of +the remote image is available locally. + +The ``rbd-mirror`` daemon is available within the optional ``rbd-mirror`` +distribution package. + +.. important:: Each ``rbd-mirror`` daemon requires the ability to connect + to both clusters simultaneously. +.. warning:: Pre-Luminous releases: only run a single ``rbd-mirror`` daemon per + Ceph cluster. + +Each ``rbd-mirror`` daemon should use a unique Ceph user ID. To +`create a Ceph user`_, with ``ceph`` specify the ``auth get-or-create`` +command, user name, monitor caps, and OSD caps:: + + ceph auth get-or-create client.rbd-mirror.{unique id} mon 'profile rbd-mirror' osd 'profile rbd' + +The ``rbd-mirror`` daemon can be managed by ``systemd`` by specifying the user +ID as the daemon instance:: + + systemctl enable ceph-rbd-mirror@rbd-mirror.{unique id} + +The ``rbd-mirror`` can also be run in foreground by ``rbd-mirror`` command:: + + rbd-mirror -f --log-file={log_path} + +.. _rbd: ../../man/8/rbd +.. _ceph-conf: ../../rados/configuration/ceph-conf/#running-multiple-clusters +.. _explicitly enabled: #enable-image-mirroring +.. _force resync command: #force-image-resync +.. _demote the image: #image-promotion-and-demotion +.. _create a Ceph user: ../../rados/operations/user-management#add-a-user +.. _mirror-snapshots: #create-image-mirror-snapshots |