Merge lp:~jtv/maas/bug-1064737 into lp:maas/trunk

[Jeroen T. Vermeulen]

Work around lxml locking up its region controller process in production (not in a branch!) when validating a malformed xpath expression as a tag definition.

See https://techknowhow.library.emory.edu/blogs/branker/2010/07/30/django-lxml-wsgi-and-python-sub-interpreter-magic

Sanity-checked with Raphael; he can't think of any problems that this might cause. Martin notes that "we probably want to use the daemon configuration for mod_wsgi longer term."

Jeroen

[Martin Packman (gz)]

So, the configuration is already using WSGIDaemonProcess which provides an alternative method of seperating different applications from each other. It seems that we do still need to set this option to avoid the sub-interpreter incompatibility, but won't lose isolation from other apps as we are already daemon'd.

review: Approve

[Raphaël Badin (rvb)]

Looks good.

review: Approve

=== modified file 'contrib/maas-http.conf'
--- contrib/maas-http.conf	2012-10-02 19:08:05 +0000
+++ contrib/maas-http.conf	2012-10-10 09:38:22 +0000
@@ -1,4 +1,10 @@
 WSGIDaemonProcess maas user=maas group=maas processes=2 threads=1 display-name=%{GROUP}
+
+# Without this, defining a tag as a malformed xpath expression will hang
+# the region controller.
+# See https://techknowhow.library.emory.edu/blogs/branker/2010/07/30/django-lxml-wsgi-and-python-sub-interpreter-magic
+WSGIApplicationGroup %{GLOBAL}
+
 WSGIScriptAlias /MAAS  /usr/share/maas/wsgi.py
 # Preload application when process starts. This will allow publishing
 # the MAAS server existence over Avahi.