I have several problem after upgrading to elasticsearch, kibana, logstash v 5.6.0.
and one of issue cannot assign unassign shard because to many open files. i have incresea open files limit to 20480 and set vm.max_map_count=262144 and still cannot assign .
That is far too much. Please read this blog post with guidance on shards and sharding, and then try to reduce that dramatically by deleting and/or reindexing data. Restoring that many shards will take time, and I am not aware of any way to speed it up, so suspect you will have to wait.
Once the cluster is back up you can try to temporarily close some indices in order to make the cluster easier to work with.
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