Thank you, Valentin.

There is something I am missing. Please see the start of the error.log below,

2018/03/04 14:05:50 [notice] 5144#9212: using the "select" event method
2018/03/04 14:05:50 [notice] 5144#9212: using the "select" event method
2018/03/04 14:05:50 [notice] 5144#9212: nginx/1.12.2
2018/03/04 14:05:50 [notice] 5144#9212: nginx/1.12.2
2018/03/04 14:05:50 [info] 5144#9212: OS: 260200 build:9200, "", suite:300, type:1
2018/03/04 14:05:50 [notice] 5144#9212: start worker processes
2018/03/04 14:05:50 [notice] 5144#9212: start worker processes
2018/03/04 14:05:50 [notice] 5144#9212: start worker process 13648
2018/03/04 14:05:50 [notice] 5144#9212: start worker process 13648
2018/03/04 14:05:51 [notice] 13648#4924: nginx/1.12.2
2018/03/04 14:05:51 [notice] 13648#4924: nginx/1.12.2
2018/03/04 14:05:51 [info] 13648#4924: OS: 260200 build:9200, "", suite:300, type:1
2018/03/04 14:05:51 [notice] 13648#4924: create thread 17496
2018/03/04 14:05:51 [notice] 13648#4924: create thread 17496
2018/03/04 14:05:51 [notice] 13648#4924: create thread 16328
2018/03/04 14:05:51 [notice] 13648#4924: create thread 16328
2018/03/04 14:05:51 [notice] 13648#4924: create thread 13940
2018/03/04 14:05:51 [notice] 13648#4924: create thread 13940

There is a single process (worker_processes 1 in the nginx.conf), with seemingly three threads (not sure why the lines in the log file are duplicated). Is the purpose of the additional threads to read static files (from the server)?