CCS Calendar and Contacts Server failed to start ccs_init: ImportError: No module named core

Symptoms

Attempting to start CCS fails with the following error:

Apr 27 10:35:40 server.no ccs_init[437335]: import pg8000 as postgres
Apr 27 10:35:40 server.no ccs_init[437335]: File "/opt/cpanel-ccs/.develop/virtualenv/lib/python2.7/site-packages/pg8000/__init__.py", line 1, in <module>
Apr 27 10:35:40 server.no ccs_init[437335]: from .core import (
Apr 27 10:35:40 server.no ccs_init[437335]: ImportError: No module named core
Apr 27 10:35:40 server.no systemd[1]: cpanel-ccs.service: control process exited, code=exited status=1
Apr 27 10:35:40 server.no systemd[1]: Failed to start Apple Calendar Server.
-- Subject: Unit cpanel-ccs.service has failed
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
--
-- Unit cpanel-ccs.service has failed.
--
-- The result is failed.

Description 

The CCS CalendarServer includes many python modules imported at startup via the ccs_init process. If these files get corrupted or suddenly go missing, it will prevent the CalendarServer from restarting successfully. For example, an emergency shutdown or file system corruption could cause these files to go missing.

Workaround

Reinstall the CCS package to stage the missing files.

yum reinstall cpanel-ccs-calendarserver