None of Configured nodes are available

org.elasticsearch.client.transport.NoNodeAvailableException: None of the configured nodes are available: [{#transport#-1}

The elastic search works fine most of the time, This error persisted for almost a minute and all my requests were 500 Error at the time.

When I checked the Elasticsearch monitoring, Kibana shows a system load of 10 at the moment.

Can you please help me on this ?

Please provide information about versions, size and configuration of you cluster. Please also include error messages from the logs that may help.