Apache resource failed to start in Pacemaker

I am using Pacemaker with Corosync to set up a basic Apache HA cluster with 3 nodes running CentOS7. For some reasons, I cannot get the apache resource started in pcs. Cluster IP: 192.168.200.40 # pcs resource show ClusterIP Resource: ClusterIP (class=ocf provider=heartbeat type=IPaddr2) Attributes: cidr_netmask=24 ip=192.168.200.40 Operations: monitor interval=20s (ClusterIP-monitor-interval-20s) start interval=0s timeout=20s (ClusterIP-start-interval-0s) stop interval=0s timeout=20s (ClusterIP-stop-interval-0s) # pcs resource show WebServer Resource: WebServer (class=ocf provider=heartbeat type=apache) Attributes: configfile=/etc/httpd/conf/httpd.conf statusurl=http://localhost/server-status Operations: monitor interval=1min (WebServer-monitor-interval-1min) start interval=0s timeout=40s (WebServer-start-interval-0s) stop interval=0s timeout=60s (WebServer-stop-interval-0s) # pcs status Cluster name: WARNING: corosync and pacemaker node names do not match (IPs used in setup?) Stack: corosync Current DC: server3.example.com (version 1.1.18-11.el7_5.2-2b07d5c5a9) - partition with quorum Last updated: Thu Jun 7 21:59:09 2018 Last change: Thu Jun 7 21:45:23 2018 by root via cibadmin on server1.example.com 3 nodes configured 2 resources configured Online: [ server1.example.com server2.example.com server3.example.com ] Full list of resources: ClusterIP (ocf::heartbeat:IPaddr2): Started server2.example.com WebServer (ocf::heartbeat:apache): Stopped Failed Actions: * WebServer_start_0 on server3.example.com 'unknown error' (1): call=49, status=Timed Out, exitreason='', last-rc-change='Thu Jun 7 21:46:03 2018', queued=0ms, exec=40002ms * WebServer_start_0 on server1.example.com 'unknown error' (1): call=53, status=Timed Out, exitreason='', last-rc-change='Thu Jun 7 21:45:23 2018', queued=0ms, exec=40003ms * WebServer_start_0 on server2.example.com 'unknown error' (1): call=47, status=Timed Out, exitreason='', last-rc-change='Thu Jun 7 21:46:43 2018', queued=1ms, exec=40002ms Daemon Status: corosync: active/enabled pacemaker: active/enabled pcsd: active/enabled The httpd instance is **enabled** and **running** on all three nodes. The cluster IP and individual node IPs are able to access the web page. The ClusterIP resource also works well for failover. What may go wrong for the apache resource in this case? Thank you very much! Update: Here is more information from the debug output. It seems the Apache is unable to bind to the port, but there is no error from the apache log, and systemctl status httpd gave all green on all nodes. I can open web pages via the cluster IP and each every node IP. The ClusterIP resource failover works fine, too. Any idea on why Apache resource doesn't work with pacemaker? # pcs resource debug-start WebServer --full Operation start for WebServer (ocf:heartbeat:apache) failed: 'Timed Out' (2) > stderr: ERROR: (98)Address already in use: AH00072: make_sock: could not bind to address [::]:80 (98)Address already in use: AH00072: make_sock: could not bind to address 0.0.0.0:80 no listening sockets available, shutting down AH00015: Unable to open logs > stderr: INFO: apache not running > stderr: INFO: waiting for apache /etc/httpd/conf/httpd.conf to come up > stderr: INFO: apache not running > stderr: INFO: waiting for apache /etc/httpd/conf/httpd.conf to come up > stderr: INFO: apache not running > stderr: INFO: waiting for apache /etc/httpd/conf/httpd.conf to come up > stderr: INFO: apache not running