Rejected Execution of org.elasticsearch.transport.TransportService Error

The problem that you are getting is because the bulk operations queue is full.

A node ES has many threads pools, generic, search, index, suggest, bulk, etc. In your case the problem is due to the queue of bulk operations is full.

Try adjusting the queue size of thread pool of bulk operation:

thread_pool.bulk.queue_size: 100

Or reduce the amount of bulk operations that you are sending at once.

For more details see https://www.elastic.co/guide/en/elasticsearch/reference/current/modules-threadpool.html

Try the following:

curl -XPUT localhost:9200/_cluster/settings -d '{ "transient" : { "threadpool.bulk.queue_size" : 500 } }'

Edit: And to Get current settings

curl -X GET "localhost:9200/_cluster/settings?include_defaults=true"