LP#1527731: Document enabling stable hash key ordering in mod_perl

Since several Evergreen features within mod_perl depend on hash key ordering,
and OpenSRF currently installs mod_perl, we'll document the change needed here
instead of in Evergreen.  When the mod_perl configuration moves to the
Evergreen repo, we can move the documentation.

Signed-off-by: Mike Rylander <mrylander@gmail.com>

diff --git a/README b/README
index 33476a0..53ab0b5 100644 (file)
--- a/README
+++ b/README
@@ -416,6 +416,24 @@ srfsh# request opensrf.math add 2,2
 +
 You should receive the value `4`.
 
+Configure the Apache server
+---------------------------
+
+OpenSRF provides several access mechanisms exposed through the Apache web
+server.  Support for mod_perl-based applications is a key feature, and requires
+a small amount of Apache configuration beyond application-specific needs.
+
+To support the interchange of Perl hashes and JSON objects, OpenSRF needs to
+depend on repeatable hash key ordering which Perl versions greater than 5.18
+intentionally disable.  To reenable this in mod_perl, add the following to
+/etc/default/apache2 on Debian distributions, or /etc/default/rcS on Ubuntu
+distributions:
+
+[source, bash]
+---------------------------------------------------------------------------
+PERL_HASH_SEED=0
+---------------------------------------------------------------------------
+
 Optional: Websockets installation instructions
 ----------------------------------------------
 Websockets are new to OpenSRF 2.4+ and are required for operating the new web-based