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From Yavor Yanchev <ya...@yanchev.com>
Subject Multiple Java installations on RH-based distros
Date Mon, 28 Mar 2016 09:09:03 GMT
Hi All,

I want to discuss a case when RH-based VM is provisioned and the image 
comes with pre-installed java 6 or 7, but the BP requires latest java 
(java 8 as of now).
This particular case is rare for now, because Brooklyn specifies java 7 
by default, but it will became common when java 8 is set as the version 
expected by Brooklyn.

RH-based distros usually use the openjdk SRPMs provided by RedHat and 
then just recompile them. All SRPMs have a SPEC file used during its 
rebuild. It specifies how the particular java version will be installed 
and what will be the *priority* in case of multiple versions. The 
*priority* itself is passed as a configuration parameter to the 
*alternatives* executable [1].
OpenJDK 6 and 7 packages use priority similar to *1700%{updatever}*, but 
OpenJDK 8 - 18%{updatever}.
When VM is provisioned and the image contains JDK 6 or 7 the already 
installed java version has much higher priority than the expected one 
for JDK8. For example:
JDK 6 will have a priority number as 160075, and then JDK 8 will have 
1875 - *1600075 > 1875*
The provisioned VM will have 2 versions of java, but the one with the 
higher priority will be used. It will be a problem with the deployed 
software if it requires Java 8.

It seems that it is a intended behavior described in RedHat's bug 
tracking system [2]

We have the following options to address the issue:
1. Leave it as it is and update the docs so the users are aware, if they 
use images with per-installed Java packages
2. Provide a post-install configuration (using the *alternatives* tool) 
to ensure that the intended java version is set as a default option
3. Ensure that all previously installed java versions are removed (yum 
remove) , before installing Java 8

Maybe option 2) is preferable, but not entirely sure for the BYON or 
SameServer scenarios where we can find a java version that is used by an 
already installed applications.

What do you think will be the best approach to fix and/or workaround it?

Regards,
Yavor

[1] 
https://access.redhat.com/documentation/en-US/JBoss_Enterprise_Application_Platform/6/html/Administration_and_Configuration_Guide/Configure_the_Default_JDK_on_Red_Hat_Enterprise_Linux.html
[2] https://bugzilla.redhat.com/show_bug.cgi?id=1175457#c33


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