If you have seen a number of your indices recently "disappear", and then when checking your logs you see they have been deleted, and you can also see other log entries that mention the term
meow, like this;
[t19hfzgnp7-meow] creating index, cause [api], templates , shards /, mappings
You are likely running a cluster that is exposed to the internet with no protection, and have been hit by the "meow attack".
Your immediate steps should be to upgrade to at least Elasticsearch 6.8.0 or 7.1.0, which includes free security functionality, containing;
- TLS for encrypted communications
- File and native realm for creating and managing users
- Role-based access control for controlling user access to cluster APIs and indexes; also allows multi-tenancy for Kibana with security for Kibana Spaces