Why it matters

Upgrades safely without downtime require rolling process. Understanding shapes ops.

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The architecture

Compatibility matrix: check source + target versions supported.

Rolling: upgrade nodes one at a time; cluster serves throughout.

Upgrade processCompatibility checkmatrix + release notesRolling upgradeone node at a timeClient version compatwire + APIUpgrade masters first, then RegionServers; client upgrades separately
Rolling upgrade steps.
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How it works end to end

Order: HDFS (if needed), ZooKeeper, HMaster (standby first), RegionServers.

Backup: snapshot critical tables before starting.

Testing: verify in staging first.

Rollback: harder mid-upgrade; plan carefully.