- Upgrading from 0.18 requires issuing a full flush of all the indices in the cluster (
curl host:9200/_flush) before shutting down the cluster, with no indexing operations happening after the flush.
- The local gateway state structure has changed, a backup of the state files is created when upgrading, they can then be used to downgrade back to 0.18. Don’t downgrade without using them.
- elasticsearch fails to start due to verification error (#2051)