49 lines
2.0 KiB
Plaintext
49 lines
2.0 KiB
Plaintext
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[role="xpack"]
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[testenv="platinum"]
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[[ccr-upgrading]]
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== Upgrading clusters
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Clusters that are actively using {ccr} require a careful approach to upgrades.
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Otherwise index following may fail during a rolling upgrade, because of the
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following reasons:
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* If a new index setting or mapping type is replicated from an upgraded cluster
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to a non-upgraded cluster then the non-upgraded cluster will reject that and
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will fail index following.
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* Lucene is not forwards compatible and when index following is falling back to
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file based recovery then a node in a non-upgraded cluster will reject index
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files from a newer Lucene version compared to what it is using.
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Rolling upgrading clusters with {ccr} is different in case of uni-directional
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index following and bi-directional index following.
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[float]
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=== Uni-directional index following
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In a uni-directional setup between two clusters, one cluster contains only
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leader indices, and the other cluster contains only follower indices following
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indices in the first cluster.
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In this setup, the cluster with follower indices should be upgraded
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first and the cluster with leader indices should be upgraded last.
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If clusters are upgraded in this order then index following can continue
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during the upgrade without downtime.
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Note that a chain index following setup can also be upgraded in this way.
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For example if there is a cluster A that contains all leader indices,
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cluster B that follows indices in cluster A and cluster C that follows
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indices in cluster B. In this case the cluster C should be upgraded first,
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then cluster B and finally cluster A.
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[float]
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=== Bi-directional index following
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In a bi-directional setup between two clusters, each cluster contains both
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leader and follower indices.
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When upgrading clusters in this setup, all index following needs to be paused
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using the {ref}/ccr-post-pause-follow.html[pause follower API] prior to
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upgrading both clusters. After both clusters have been upgraded then index
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following can be resumed using the
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{ref}/ccr-post-resume-follow.html[resume follower API]].
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