ccaeae4706
Make the ring sync code clearer and improve logic around leader switching during or after a sync. Also add more debug logs to make it easier to debug when things go wrong. Closes-Bug: 1448884 Change-Id: I10d51c74001710b6b7a2502e14370996b15ffb40
30 lines
1.4 KiB
Plaintext
30 lines
1.4 KiB
Plaintext
== Swift Charm Ring Management ==
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Swift uses rings and builders to manage data distribution across storage devices
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in the cluster. More information on this can be found in the upstream
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documentation [0].
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In order to function correctly, the rings and builders need to be the same
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across all swift proxy units and the rings need to be distributed to storage
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units. The swift proxy charm achieves this by electing a leader unit and having
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that unit manage ring and builder files by updating them when new nodes or
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devices are added to the cluster and distributing those files to other nodes in
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the cluster.
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Since over time the leader may change, rings syncs use acknowledgements from
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peer units to determine whether a synchronisation has completed. This was if
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the leader switches to another unit, we are able to know that that unit has
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up-to-date ring and builder files.
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When new devices are added to storage units, the leader proxy unit is notified
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and adds them to the ring. Once complete, the leader unit will broadcast a
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notification that rings and builders are ready to be synced across the cluster
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(only proxy units get builders) and each unit in the cluster should then begin
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syncing from the leader and acknowledge receipt.
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During synchronisation, swift-proxy services are stopped in order to avoid
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having requests being handled while rings are being updated.
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[0] http://docs.openstack.org/developer/swift/overview_ring.html
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