The problem with "push" style solutions is that they are not indempotent,
which means that they would execute commands and scripts imperatively
without first checking whether or not they ought to do so.  This might
cause unintended side effects.

It is of course possible to write "if" checks virtually everywhere and
micromanage every script to check before execute like what python cuisine
does with its _ensure idiom but this approach can be quite hackish and
bulks up your fabric script significantly.

"Push only" approaches are fine for small scale stuff (2-10 servers), but
once you have a lot of servers, a push system will begin to show its
limits, unless of course you implement multiprocessing in your scripts.

"Pull" type solutions on the other hand are declarative (i.e. indempotent)
in nature, so no silly "if" checks everywhere; but the downside is that
they are much more complex and time consuming to implement .

Which is why people usually use a mix of push-and-pull in a real life
deployment.
*  Push-style scripts for provisioning application code and services.
*  Pull-type solutions for initial server configuration and configuration
file management (managing conf files for postgresql, memcached, task
server, web server, other specialised services with a conf file etc).

On Fri, May 18, 2012 at 10:50 PM, Benjamin Scherrey <proteus...@gmail.com>wrote: