Elastic won't start after upgrade to 8.19.4

Elastic Stack Elasticsearch
1

We recently attempted to upgrade our cluster from 8.17.4 to 8.19.4 using apt. After the upgrade, the service won’t start and we see this line in the logs:

java.lang.IllegalStateException: Failed to parse mappings for index [[.kibana-observability-ai-assistant-kb-000001/UgwoSBEkQPqRj-ItbDSGdA]]

and:

Caused by: org.elasticsearch.index.mapper.MapperParsingException: Failed to parse mapping: [semantic_text] is available on indices created with 8.11 or higher.

Are we toast?

2

Well, I would hope not. But did you create snapshot before the upgrade?

Can you explain a bit more on current state - the cluster size/topology, how many nodes were upgraded before you saw the error, how (precisely) did you upgrade?

3

We have a two-node cluster running on bare metal. So no snapshots. We issued apt upgrade on each node. Edit: I should add that we don’t mind partial data loss. I tried to find the index containing the problematic data, but couldn’t locate it anywhere in the cluster.