Apache oddness on jessie => stretch upgrade

[Dave Sherohman <dave@sherohman.org>]

Yesterday, I started on upgrading my servers from jessie to stretch.  It
went mostly without incident at the time, but then apache failed to
restart after logrotate did its thing overnight.

Investigating the apache error log, it ended with:

[Tue Aug 22 06:30:01.223322 2017] [mpm_prefork:notice] [pid 32366] AH00171: Graceful restart requested, doing restart
apache2: Syntax error on line 146 of /etc/apache2/apache2.conf: Syntax error on line 2 of /etc/apache2/mods-enabled/access_compat.load: Cannot load /usr/lib/apache2/modules/mod_access_compat.so into server: /usr/lib/apache2/modules/mod_access_compat.so: undefined symbol: ap_get_useragent_host

The particularly odd part is that this seems to happen only on the first
restart after the upgrade.  If I manually `systemctl start apache2` or
`apachectl graceful`, it successfully starts up with no complaints.
I'll have to wait until tomorrow to see whether this recurs on the next
logrotate run.

Any ideas regarding what's happening here or how to prevent it (other
than doing a manual apache restart immediately after upgrading, to get
the failure out of the way)?


Also, side question: I'm also manually running `systemctl enable
apache2` after upgrading.  How can you tell whether something is enabled
or not in systemd?  `systemctl status` will tell you whether it's
currently running or not, but I can't find any indication of enabled/
disabled in its output.

-- 
Dave Sherohman