Puppet users - Oct 2010 - require service started at another node

Hello,
Anybody now how make with puppet dependence on other service on
another node?

like :  require => Service[dbnode:postgresql]
I need ensure that the db is running on another node before start my
appserver.

Thank you.

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On Fri, Oct 29, 2010 at 04:56:34AM -0700, Leonko wrote:
> Hello,
> Anybody now how make with puppet dependence on other service on
> another node?
> 
> like :  require => Service[dbnode:postgresql]
> I need ensure that the db is running on another node before start my
> appserver.
You can''t do this directly.  Even if you were to use storeconfigs to
get
at facts about other nodes, all that would tell you is that the database
service was running the last time puppet ran on that node.  Besides, the
important thing to know, even more important than whether the service is
running on the dbnode, is whether you can usefully connect to the
service from your appserver node.  Even if the service is running, other
things might prevent that.

I think the best approach would be to have a test that runs on your
appservernode, connects to your postgres server and does a simple status
check.  You could do this as a custom fact, so that it set a variable
like $dbservice to true or false, or you could do it as an exec.

But can your application server really not cope with the database
service not being available?  Can they not present a useful error
message if the database is broken?  How will you cope if the database
service dies once your appserver has started?

-- 
Bruce

If the universe were simple enough to be understood, we would be too
simple to understand it.

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You can try using something like
http://github.com/puppetlabs/puppet-external-resource

Ohad

On Fri, Oct 29, 2010 at 1:56 PM, Leonko <the.leonko@gmail.com> wrote:
> Hello,
> Anybody now how make with puppet dependence on other service on
> another node?
>
> like :  require => Service[dbnode:postgresql]
> I need ensure that the db is running on another node before start my
> appserver.
>
> Thank you.
>
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>
>
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Hello, Bruce. At now we have hard dependence between file storage, db
server and appserver. If it chain broken at any phase we get the
message from zabbix. And we try it automatize this action.

On 29 окт, 21:53, Bruce Richardson <itsbr...@workshy.org>
wrote:
> On Fri, Oct 29, 2010 at 04:56:34AM -0700, Leonko wrote:
> But can your application server really not cope with the database
> service not being available?  Can they not present a useful error
> message if the database is broken?  How will you cope if the database
> service dies once your appserver has started?
>
> --
> Bruce
>
> If the universe were simple enough to be understood, we would be too
> simple to understand it.
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Thanks, but  I didn''t understand how it works. Maybe you know
documentation for this module?

On 29 окт, 22:09, Ohad Levy <ohadl...@gmail.com>
wrote:
> You can try using something
likehttp://github.com/puppetlabs/puppet-external-resource
>
> Ohad
>
> On Fri, Oct 29, 2010 at 1:56 PM, Leonko <the.leo...@gmail.com> wrote:
> > Hello,
> > Anybody now how make with puppet dependence on other service on
> > another node?
>
> > like :  require => Service[dbnode:postgresql]
> > I need ensure that the db is running on another node before start my
> > appserver.
>
> > Thank you.
>
> > --
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> > .
> > For more options, visit this group at
> >http://groups.google.com/group/puppet-users?hl=en.
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On Sun, Oct 31, 2010 at 11:44:51PM -0700, Leonko wrote:
> Hello, Bruce. At now we have hard dependence between file storage, db
> server and appserver. If it chain broken at any phase we get the
> message from zabbix.
But that''s not a problem.  Zabbix is monitoring software: it *should*
tell you when important services are broken.
> And we try it automatize this action.
Fine.  But you can''t use a single puppet run to make it all happen. 
Use
puppet on the database server to make sure that postgresql is running
properly and use puppet on the application host to make sure that the
application server is running *if* the database server is available.
Puppet can automate that much for you.

If you want to have the minimum time between the database server coming
up and the application server starting, there are a number of ways you
could do that; the application host could be checking the db connection
on a regular basis, for instance, or the db server could signal the
application host once the app is up.  But really, your best plan is to

 1.  Make sure that your database service is up early, as resilient as
you can make it and rarely restarted.

 2.  Make your application server tolerant of database downtime (that
is, have the applications generate sensible errors while the db is down
and recover when it is up, rather than just crash and require an
application server restart).


-- 
Bruce

Bitterly it mathinketh me, that I spent mine wholle lyf in the lists
against the ignorant.  -- Roger Bacon, "Doctor Mirabilis"

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>
>  1.  Make sure that your database service is up early, as resilient as
> you can make it and rarely restarted.
>
Thank you. Maybe you know method to validate what db is start early.
It''s very important for me.

>  2.  Make your application server tolerant of database downtime (that
> is, have the applications generate sensible errors while the db is down
> and recover when it is up, rather than just crash and require an
> application server restart).
If appserver (java app server like jboss)  start and can''t find db
it''s crash and need to restart by hand.  We are unable to do anything
with it.
>
> --
> Bruce
>
> Bitterly it mathinketh me, that I spent mine wholle lyf in the lists
> against the ignorant.  -- Roger Bacon, "Doctor Mirabilis"
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On Nov 1, 2010, at 12:57 AM, Leonko wrote:
> 
>> 
>>  1.  Make sure that your database service is up early, as resilient as
>> you can make it and rarely restarted.
>> 
> 
> Thank you. Maybe you know method to validate what db is start early.
> It''s very important for me.
> 
> 
>>  2.  Make your application server tolerant of database downtime (that
>> is, have the applications generate sensible errors while the db is down
>> and recover when it is up, rather than just crash and require an
>> application server restart).
> 
> If appserver (java app server like jboss)  start and can''t find db
> it''s crash and need to restart by hand.  We are unable to do
anything
> with it.
Can you give your app a babysitter wrapper service?  This sounds like it might
be useful just for uptime.

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2010/11/1 Leonko <the.leonko@gmail.com>
> [...]
> >  2.  Make your application server tolerant of database downtime (that
> > is, have the applications generate sensible errors while the db is
down
> > and recover when it is up, rather than just crash and require an
> > application server restart).
>
> If appserver (java app server like jboss)  start and can''t find db
> it''s crash and need to restart by hand.  We are unable to do
anything
> with it.
>
Make a start script for the Appserver which do the steps for you:

#! /bin/sh

checkdb () {
  [... code to check if DB is up ...]
}

startdb () {
  [... code to start DB if down ...]
}

startApp () {
  [... code to start App if down ...]
}

if [ ! $(checkdb) ]; then
  startdb
  sleep 60
  if [ ! $(checkdb) ]; then
    echo "Failed, couldn''t start DB!"; exit
  else
    startApp
  fi
fi

You can also implement it as a watchdog if you put your code in a construct
like this:

while true; do
  [... start logic with checks ...]
  sleep 30
done

Kind regards, Thomas

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You can say more about it?  I do not understand what you say?

> Can you give your app a babysitter wrapper service?  This sounds like it
might be useful just for uptime.
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On Nov 1, 2010, at 1:14 AM, Leonko wrote:
> You can say more about it?  I do not understand what you say?
> 
> 
>> Can you give your app a babysitter wrapper service?  This sounds like
it might be useful just for uptime.
The idea is that you wrap this app in a service.  The wrapper is started,
stopped, and restarted like a normal service.

When the wrapper is running, ensures that your application is running.  If your
application is not running, the wrapper waits a set time and then starts your
app.  The wait time is because you don''t want to load the server by
instantly restarting.  This is because if you app crashes during startup every
time, you don''t want your server to be excessively loaded by the
restart attempts.

Stopping the wrapper stops your app.

Starting the wrapper starts your app.  (then makes sure it keeps running)

Sending a restart to the wrapper, stops the wrapper and then starts the wrapper.

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On 29 October 2010 22:56, Leonko <the.leonko@gmail.com> wrote:
> Hello,
> Anybody now how make with puppet dependence on other service on
> another node?
>
> You could try looking at it like an application control problem and use
tools that sit on top of puppet - like ControlTier -
http://blog.controltier.com/2009/04/new-whitepaper-achieving-fully.html

john

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Thank you. But I think I prefer "func"  for this job and start it from
main node

On Nov 1, 11:12 am, Thomas Bendler <thomas.bend...@cimt.de>
wrote:
> 2010/11/1 Leonko <the.leo...@gmail.com>
>
> > [...]
> > >  2.  Make your application server tolerant of database downtime
(that
> > > is, have the applications generate sensible errors while the db
is down
> > > and recover when it is up, rather than just crash and require an
> > > application server restart).
>
> > If appserver (java app server like jboss)  start and can''t
find db
> > it''s crash and need to restart by hand.  We are unable to do
anything
> > with it.
>
> Make a start script for the Appserver which do the steps for you:
>
> #! /bin/sh
>
> checkdb () {
>   [... code to check if DB is up ...]
>
> }
>
> startdb () {
>   [... code to start DB if down ...]
>
> }
>
> startApp () {
>   [... code to start App if down ...]
>
> }
>
> if [ ! $(checkdb) ]; then
>   startdb
>   sleep 60
>   if [ ! $(checkdb) ]; then
>     echo "Failed, couldn''t start DB!"; exit
>   else
>     startApp
>   fi
> fi
>
> You can also implement it as a watchdog if you put your code in a construct
> like this:
>
> while true; do
>   [... start logic with checks ...]
>   sleep 30
> done
>
> Kind regards, Thomas
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Thank you. It''s real helpful.

On Nov 1, 1:12 pm, John Warburton <jwarbur...@gmail.com>
wrote:
> On 29 October 2010 22:56, Leonko <the.leo...@gmail.com> wrote:
>
> > Hello,
> > Anybody now how make with puppet dependence on other service on
> > another node?
>
> > You could try looking at it like an application control problem and
use
>
> tools that sit on top of puppet - like ControlTier
-http://blog.controltier.com/2009/04/new-whitepaper-achieving-fully.html
>
> john
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> >  2.  Make your application server tolerant of database downtime (that
> > is, have the applications generate sensible errors while the db is
down
> > and recover when it is up, rather than just crash and require an
> > application server restart).
> 
> If appserver (java app server like jboss)  start and can''t find db
> it''s crash and need to restart by hand.  We are unable to do
anything
> with it.
Then you need to rethink how you design and deploy your java
applications.  I have worked with Java, Tomcat, Jboss and similar
systems; it is perfectly possible to deploy java applications in a way
which allows them to cope with the temporary absence of a database
server.

-- 
Bruce

Bitterly it mathinketh me, that I spent mine wholle lyf in the lists
against the ignorant.  -- Roger Bacon, "Doctor Mirabilis"

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