Re(2): [Fab-user] Revert deployments

[Miguel A. Lamy]

Hi Christian,

I think I can figure out now a solution to my problem.

Thanks a lot.

Miguel Lamy


address@hidden on segunda-feira, 19 de Janeiro de 2009 at 19:06  wrote:
:On Mon, Jan 19, 2009 at 7:03 PM, Miguel A. Lamy <address@hidden> wrote:
:> Hi all,
:>
:> I am evaluating Fabric and a I'm bit lost sorry... I think I'm putting dumb 
question.
:>
:> I want to deploy Java Web application into several servers. In the past I 
used some shell scripts that
:stoped
:> myservers, rsynced my app to the servers, backuped the databases (Mysql, 
SqlServer and Oracle) and started
:> the application server (tipical Jboss and Oracle). I use ssh in all servers 
with public keys.
:>
:> I was doing the deployment  server by server and sometimes the process 
didn't run as expected and I have
:> crashs during the startup of the application because of some program errors 
or inconsistency in the
:databases.
:
:A tool such as Fabric works best in homogeneous environments, ie. when
:all database servers are alike and all application servers are alike.
:In this mindset, any inconsistencies in the environment are bugs.
:
:When each server is different, then each server must be handled
:differently. This encourages fiddling, and fiddling leads to mistakes,
:and mistakes leads to... suffering.... in the form of down time, ahem.
::)
:
:That said, Fabric is a pretty generic remote automation tool. :)
:
:>
:> So I thought may be I can use some tool out there that simplify that work 
and revert my process with no
:> pain...
:>
:> I read some documentation from Fabric site and from the github.com but still 
don't know how can I run
:> myscripts in a way that can "detect" errors in deployment and run some 
rollback code that reverts errors
:> during the deployment.
:
:Fabric cannot undo arbitrary shell commands.
:
:Fabric runs with a fail-fast mentality by default, but this can be
:overwriten on most remote operations by setting a `fail` kwarg to
:either "ignore" or "warn". When you invoke an operation, the call can
:be wrapped with a `try ... except SystemExit` of sorts, and that will
:give you a chance to do something when bad stuff happens.
:
:But what I usually do is to just implement a "rollback" command in my
:fabfile, and when I see that my deployment have failed, I can then
:decide whether to run it or not.
:
:>
:> I understand that I can use variables to store command result status and 
define rollback commands that can
:be
:> executed but my question is... can Fabric "detect" errors and automatically 
execute rollback functions in
:> case of some trouble ?
:
:An "error", in the sense of invoking some remote shell command, is
:when that command returns with a code other than 0.
:
:Fabric detects this and acts upon it in accord to the "fail" kwarg for
:that particular operation, which is "abort" by default.
:
:Aborting works by throwing SystemExit, and this is something that you
:can catch. However, Fabric was not designed with this use case in
:mind, to there is no additional information about what failed encoded
:in that exception.
:
:>
:> I want to deploy several servers and not be worried if one server didn't 
deployed correctly at 2.00AM and
:the
:> application server didn't start because of that failure. That server should 
automatically recover from that
:> bad deploy, revert to the previous status so in the morning I can analyse 
the errors and correct that
:errors
:> not worried that users can't run my application because of that failure.
:
:This is possible to do by calling your own "rollback" command in the
:except clause mentioned above.
:
:>
:> I'd appreciate any help given :-)
:>
:> (Sorry for my poor english)
:>
:> Miguel Lamy
:>
:>
:>
:> _______________________________________________
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:> address@hidden
:> http://lists.nongnu.org/mailman/listinfo/fab-user
:>
:
:
:
:-- 
:Venlig hilsen / Kind regards,
:Christian Vest Hansen.