Downgrading an Elasticsearch node to an earlier version is unsupported, because
we do not make any attempt to guarantee that a node can read any of the on-disk
data written by a future version. Yet today we do not actively prevent
downgrades, and sometimes users will attempt to roll back a failed upgrade with
an in-place downgrade and get into an unrecoverable state.
This change adds the current version of the node to the node metadata file, and
checks the version found in this file against the current version at startup.
If the node cannot be sure of its ability to read the on-disk data then it
refuses to start, preserving any on-disk data in its upgraded state.
This change also adds a command-line tool to overwrite the node metadata file
without performing any version checks, to unsafely bypass these checks and
recover the historical and lenient behaviour.
Added documentation for node repurpose tool and included documentation on how to repurpose nodes safely. Adjusted order of tools in `elasticsearch-node` tool since the repurpose tool is most likely to be used.
Co-Authored-By: David Turner <david.turner@elastic.co>
This commit, mostly authored by @DaveCTurner,
adds documentation for elasticsearch-node tool #37696.
(cherry picked from commit 09425d5a5158c2d3fdad794411b3bbc4bba47b15)
David Turner
Henning Andersen
Andrey Ershov