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105 lines
3.7 KiB
ReStructuredText
105 lines
3.7 KiB
ReStructuredText
================
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Host Maintenance
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================
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All hosts that support Ceph daemons need to support maintenance activity, whether the host
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is physical or virtual. This means that management workflows should provide
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a simple and consistent way to support this operational requirement. This document defines
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the maintenance strategy that could be implemented in cephadm and mgr/cephadm.
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High Level Design
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=================
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Placing a host into maintenance, adopts the following workflow;
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#. confirm that the removal of the host does not impact data availability (the following
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steps will assume it is safe to proceed)
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* ``orch host ok-to-stop <host>`` would be used here
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#. if the host has osd daemons, apply noout to the host subtree to prevent data migration
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from triggering during the planned maintenance slot.
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#. Stop the ceph target (all daemons stop)
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#. Disable the ceph target on that host, to prevent a reboot from automatically starting
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ceph services again)
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Exiting Maintenance, is basically the reverse of the above sequence
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Admin Interaction
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=================
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The ceph orch command will be extended to support maintenance.
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.. code-block::
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ceph orch host enter-maintenance <host> [ --check ]
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ceph orch host exit-maintenance <host>
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.. note:: In addition, the host's status should be updated to reflect whether it
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is in maintenance or not.
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The 'check' Option
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__________________
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The orch host ok-to-stop command focuses on ceph daemons (mon, osd, mds), which
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provides the first check. However, a ceph cluster also uses other types of daemons
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for monitoring, management and non-native protocol support which means the
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logic will need to consider service impact too. The 'check' option provides
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this additional layer to alert the user of service impact to *secondary*
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daemons.
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The list below shows some of these additional daemons.
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* mgr (not included in ok-to-stop checks)
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* prometheus, grafana, alertmanager
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* rgw
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* haproxy
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* iscsi gateways
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* ganesha gateways
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By using the --check option first, the Admin can choose whether to proceed. This
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workflow is obviously optional for the CLI user, but could be integrated into the
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UI workflow to help less experienced Administators manage the cluster.
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By adopting this two-phase approach, a UI based workflow would look something
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like this.
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#. User selects a host to place into maintenance
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* orchestrator checks for data **and** service impact
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#. If potential impact is shown, the next steps depend on the impact type
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* **data availability** : maintenance is denied, informing the user of the issue
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* **service availability** : user is provided a list of affected services and
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asked to confirm
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Components Impacted
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===================
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Implementing this capability will require changes to the following;
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* cephadm
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* Add maintenance subcommand with the following 'verbs'; enter, exit, check
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* mgr/cephadm
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* add methods to CephadmOrchestrator for enter/exit and check
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* data gathering would be skipped for hosts in a maintenance state
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* mgr/orchestrator
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* add CLI commands to OrchestratorCli which expose the enter/exit and check interaction
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Ideas for Future Work
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=====================
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#. When a host is placed into maintenance, the time of the event could be persisted. This
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would allow the orchestrator layer to establish a maintenance window for the task and
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alert if the maintenance window has been exceeded.
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#. The maintenance process could support plugins to allow other integration tasks to be
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initiated as part of the transition to and from maintenance. This plugin capability could
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support actions like;
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* alert suppression to 3rd party monitoring framework(s)
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* service level reporting, to record outage windows
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