Tried to reproduce this bug by modifying api_worker in tacker.conf file.

First checked for api_workers = 4, and got the below workers started successfully:

ps aux | grep tacker
open       1239  0.2  0.9 243328 78568 ?        Ss   01:02   0:02 /usr/bin/python /usr/local/bin/tacker-conductor --config-file /etc/tacker/tacker.conf
open       6795  0.0  0.1 107880  8820 pts/5    S+   01:05   0:00 journalctl -n 10000 -a -f --unit <email address hidden>
root       7438  8.4  0.9 245480 80648 ?        Ss   01:19   0:02 /usr/bin/python /usr/local/bin/tacker-server --config-file /etc/tacker/tacker.conf
root       7448  3.9  1.3 296348 113608 ?       S    01:19   0:00 /usr/bin/python /usr/local/bin/tacker-server --config-file /etc/tacker/tacker.conf
root       7449  4.0  1.3 296356 113612 ?       S    01:19   0:01 /usr/bin/python /usr/local/bin/tacker-server --config-file /etc/tacker/tacker.conf
root       7450  4.1  1.3 296352 113604 ?       S    01:19   0:01 /usr/bin/python /usr/local/bin/tacker-server --config-file /etc/tacker/tacker.conf
root       7451  4.0  1.3 296344 113604 ?       S    01:19   0:01 /usr/bin/python /usr/local/bin/tacker-server --config-file /etc/tacker/tacker.conf
root       7452  0.1  1.3 297124 111736 ?       S    01:19   0:00 /usr/bin/python /usr/local/bin/tacker-server --config-file /etc/tacker/tacker.conf
root       7453  0.1  1.3 297128 111684 ?       S    01:19   0:00 /usr/bin/python /usr/local/bin/tacker-server --config-file /etc/tacker/tacker.conf
root       7454  0.1  1.3 297124 111736 ?       S    01:19   0:00 /usr/bin/python /usr/local/bin/tacker-server --config-file /etc/tacker/tacker.conf
root       7455  0.1  1.3 297128 111684 ?       S    01:19   0:00 /usr/bin/python /usr/local/bin/tacker-server --config-file /etc/tacker/tacker.conf
root       7456  0.1  1.3 297128 111708 ?       S    01:19   0:00 /usr/bin/python /usr/local/bin/tacker-server --config-file /etc/tacker/tacker.conf
root       7457  0.1  1.3 297124 111696 ?       S    01:19   0:00 /usr/bin/python /usr/local/bin/tacker-server --config-file /etc/tacker/tacker.conf
root       7458  0.1  1.3 297172 111740 ?       S    01:19   0:00 /usr/bin/python /usr/local/bin/tacker-server --config-file /etc/tacker/tacker.conf
root       7459  0.2  1.3 297132 111684 ?       S    01:19   0:00 /usr/bin/python /usr/local/bin/tacker-server --config-file /etc/tacker/tacker.conf
root       7460  0.1  1.3 297128 111688 ?       S    01:19   0:00 /usr/bin/python /usr/local/bin/tacker-server --config-file /etc/tacker/tacker.conf
root       7461  0.1  1.3 297124 111688 ?       S    01:19   0:00 /usr/bin/python /usr/local/bin/tacker-server --config-file /etc/tacker/tacker.conf
root       7462  0.1  1.3 297176 111736 ?       S    01:19   0:00 /usr/bin/python /usr/local/bin/tacker-server --config-file /etc/tacker/tacker.conf
root       7463  0.1  1.3 297124 111712 ?       S    01:19   0:00 /usr/bin/python /usr/local/bin/tacker-server --config-file /etc/tacker/tacker.conf
root       7464  0.1  1.3 297128 111712 ?       S    01:19   0:00 /usr/bin/python /usr/local/bin/tacker-server --config-file /etc/tacker/tacker.conf
root       7465  0.1  1.3 297036 111728 ?       S    01:19   0:00 /usr/bin/python /usr/local/bin/tacker-server --config-file /etc/tacker/tacker.conf
root       7466  0.2  1.3 297136 111708 ?       S    01:19   0:00 /usr/bin/python /usr/local/bin/tacker-server --config-file /etc/tacker/tacker.conf
root       7467  0.1  1.3 297172 111740 ?       S    01:19   0:00 /usr/bin/python /usr/local/bin/tacker-server --config-file /etc/tacker/tacker.conf



Then checked for api_workers = 2, and got the below workers started successfully:

ps aux | grep tacker

open       1239  0.2  0.9 243328 78536 ?        Ss   01:02   0:02 /usr/bin/python /usr/local/bin/tacker-conductor --config-file /etc/tacker/tacker.conf
open       6795  0.0  0.1 107880 10352 pts/5    S+   01:05   0:00 journalctl -n 10000 -a -f --unit <email address hidden>
root       7496  6.6  0.9 245476 80460 ?        Ss   01:20   0:02 /usr/bin/python /usr/local/bin/tacker-server --config-file /etc/tacker/tacker.conf
root       7506  3.1  1.3 296348 113548 ?       S    01:20   0:00 /usr/bin/python /usr/local/bin/tacker-server --config-file /etc/tacker/tacker.conf
root       7507  3.1  1.3 296348 113548 ?       S    01:20   0:00 /usr/bin/python /usr/local/bin/tacker-server --config-file /etc/tacker/tacker.conf
root       7508  0.1  1.3 297124 111724 ?       S    01:20   0:00 /usr/bin/python /usr/local/bin/tacker-server --config-file /etc/tacker/tacker.conf
root       7509  0.1  1.3 297124 111740 ?       S    01:20   0:00 /usr/bin/python /usr/local/bin/tacker-server --config-file /etc/tacker/tacker.conf
root       7510  0.1  1.3 297124 111752 ?       S    01:20   0:00 /usr/bin/python /usr/local/bin/tacker-server --config-file /etc/tacker/tacker.conf
root       7511  0.1  1.3 297124 111736 ?       S    01:20   0:00 /usr/bin/python /usr/local/bin/tacker-server --config-file /etc/tacker/tacker.conf


So api_worker is working fine. But little bit confused about the number of active workers.
For api_workers=4 it is showing approx 17 active workers and for api_worker=2 it is showing 7 active worker.
If anyone elaborate, it will be helpful.