elasticsearch/docs/reference/migration/migrate_7_0/node.asciidoc

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[[breaking_70_node_changes]]
=== Node start up

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==== Nodes with left-behind data or metadata refuse to start
Repurposing an existing node by changing node.master or node.data to false can leave lingering on-disk metadata and
data around, which will not be accessible by the node's new role. Beside storing non-accessible data, this can lead
to situations where dangling indices are imported even though the node might not be able to host any shards, leading
to a red cluster health. To avoid this,

* nodes with on-disk shard data and node.data set to false will refuse to start
* nodes with on-disk index/shard data and both node.master and node.data set to false will refuse to start

Beware that such role changes done prior to the 7.0 upgrade could prevent node start up in 7.0.