Upgrading clusters using cross-cluster replication

Upgrading clusters using cross-cluster replication

Clusters that are actively using cross-cluster replication require a careful approach to upgrades. The following conditions could cause index following to fail during rolling upgrades:

• Clusters that have not yet been upgraded will reject new index settings or mapping types that are replicated from an upgraded cluster.
• Nodes in a cluster that has not been upgraded will reject index files from a node in an upgraded cluster when index following tries to fall back to file-based recovery. This limitation is due to Lucene not being forward compatible.

The approach to running a rolling upgrade on clusters where cross-cluster replication is enabled differs based on uni-directional and bi-directional index following.