openstack-nova-api has conflicted with the httpd service among the port 8774

Question

I can't use httpd and nova-api at the same time.
when I used httpd service.The nova-api is dead(or inactive).

#systemctl restart openstack-nova-api
OUTPUT:

Job for openstack-nova-api.service failed because the control process exited 
with error code. See "systemctl status openstack-nova-api.service" and 
"journalctl -xe" for details.   

I checked out the log,I get the error as follows.

LOG:ERROR nova.wsgi [-] Could not bind to 0.0.0.0:8774: error: [Errno 98] Address already in use.  
CRITICAL nova [-] Unhandled error: error: [Errno 98] Address already in use.  

And then,I try to find which process have used the port8774.

#netstat -tunlp | grep 8774    
OUTPUT:  
tcp    0   0 0.0.0.0:8774     0.0.0.0:*               LISTEN    61690/httpd    

When I #systemctl stop httpd->#systemctl restart nova-api->#systemctl restart http. I get a similiar mistake(I use RDO to install openstack-train version on centos 7).

they can't exist together