[Proposal] Installing RPM package shouldn't start Brooklyn

[Valentin Aitken <bo...@gmail.com>]

Hi,

This suggestion is linked to our effort to improve the overall RPM user 
experience with install, upgrade and erase actions.
Currently on installing or upgrading Apache Brooklyn from RPM the 
installer spec starts Apache Brooklyn.

Launching on first install pros and cons.
+ very easy first user experience.
- I expect users to have to tweak their credentials and other details 
and having to restart Apache Brooklyn they start using it

Launching on upgrade pros and cons:
- user will not be able to check the GUI immediately.
- If the GUI is not there
   then a new user can get bog down in other configurations details and 
delay startup additionally.
+ User can be proactive and react better if there is an error with 
installing.

Observations from Aled Sage which he made offline :
     mysql does NOT start the process - 
https://dev.mysql.com/doc/refman/5.5/en/linux-installation-rpm.html
         "In MySQL 5.5.5 and later, during a new installation using RPM 
packages, the server boot scripts are installed,
         but the MySQL server is not started at the end of the 
installation, since the status of the server during an unattended 
installation is not known."
         For upgrade:
         "if the MySQL server is running when the upgrade occurs, the 
MySQL server is stopped, the upgrade occurs, and the MySQL server is 
restarted.
         If the MySQL server is not already running when the RPM upgrade 
occurs, the MySQL server is not started at the end of the installation."
-   Elasticsearch does NOT start the process - 
https://github.com/elastic/elasticsearch/issues/3722
     MongoDB does NOT start the process - 
https://docs.mongodb.com/v3.2/tutorial/install-mongodb-on-red-hat/
     RabbitMQ does NOT start the process - 
https://www.rabbitmq.com/install-rpm.html
     Cassandra does NOT start the process - 
https://docs.datastax.com/en/cassandra/2.0/cassandra/install/installRHEL_t.html

A strange behaviour for me which I noticed is
that on CentOS 6 if the process(service) is stopped then when user do 
upgrade or erase of the rpm then the action fails.

----

Launching on upgrade.

I'd like to separate this discussion.
Ideally if Apache Brooklyn is started then we would want upgrading to 
not interrupt the process.
Putting details here how we can actually implement such behaviour.

The usual way for upgrading Apache Brooklyn is to launch the upgraded 
process in a non highAvailability mode
  e.g. HOT_BACKUP or similar in order to check persistence 
compatibility. (Better to be with a command which exits after it checks 
persistence.)
If the above gives no error then user should run the new process in 
STAND_BY and then stop the old version.
I am happy to add other points here.

The above scenario may not be easy to implement in rpm.
Before doing an actual upgrade of Apache Brooklyn application files, it 
should first extract the rpm contents in a tmp folder and
then use new temp Apache Brooklyn to execute the HOT_BACKUP check.
If that can be implemented then the next step with starting the new 
process should be easier.
rpm script should then start the new process in STAND_BY and then stop 
the old Apache Brooklyn process.

The discussion is also applicable for .deb or other installers.

-- 
Kind Regards,
Valentin Aitken!