Re: [Fab-user] Executing a block of code once for task that has multiple hosts

[Jeff Forcier]

On Wed, Oct 5, 2011 at 1:43 PM, Ahsan Rabbani <address@hidden> wrote:
> Is it possible to have certain code executed only once even if a task has
> multiple hosts defined (without having to invoke multiple tasks from the
> command line)?

In Fab 1.2 and below, one way to do this is to flip it around and use
@runs_once:

    @runs_once
    def compile():
        # This runs one time only, regardless of how many times
compile() is called

    @hosts("host1", "host2", ...)
    def compile_and_rsync():
        compile() # Innards of compile() will only actually execute once
        # but everything in here runs once per host, so rsync or whatnot.

Invoke as:

    $ fab compile_and_rsync

Fabric 1.3 will have execute(), which should feel less backwards:

    @hosts("host1", "host2", ...)
    def rsync_files(projects):
        # rsync here

    def compile_and_rsync():
        # Anything in here runs just once because we're not using @hosts.
        # (Unless you use -H, of course...)
        compile() # or whatever
        execute(rsync_files) # This honors rsync_files' @hosts and
loops over the hosts

1.3 is due out in the next week or two (hopefully sooner -- wrapping
up execute() work now -- but we're waiting on some dependency issues
that involve a third party.)

Best,
Jeff

-- 
Jeff Forcier
Unix sysadmin; Python/Ruby engineer
http://bitprophet.org