Question about the start hook

John Meinel john at
Thu Sep 4 05:32:18 UTC 2014

My understanding is that the proposed Leader spec is likely to help with
this, as a leader unit could coordinate between its peers which one should
work next. Otherwise, it is just up to the charm peer relation to
coordinate anything like this. So in peer-relation-changed you could say
that you want to perform the next step, but you are waiting for your other
peers, etc.

I think there is also a limitation that until everything has started and
joined you don't actually know how many other units there are going to be.
Though I think this is part of the "it isn't truly knowable because
something may fail to come up, you may add units at a later time, etc".

I do think we could do a better job of exposing what we think the number of
units will be "real soon now".


On Wed, Sep 3, 2014 at 11:16 PM, Marco Ceppi <marco.ceppi at>

> Hi Tim,
> Great question, sorry it took me so long to get back to you. I have an
> assumption that all hooks run serially on a single unit regardless of
> service group, etc. However, I want to say I've seen some kind
> serialization between peers. I've cc'd the Juju core mailing list and the
> regular juju mailing list to help correct and clarify these statements and
> shed some light once and for all.
> Finally, once it's been known, I'll be updating the author docs to detail
> the execution pattern in detail.
> Thanks,
> Marco Ceppi
> On Sat, Aug 30, 2014 at 6:31 AM, Humphrey, Timothy L (RIS-DAY) <
> Timothy.Humphrey at> wrote:
>> Marco,
>> Do you know the answer to my question, below? Or should I re-phase it?
>> Tim
>> -----Original Message-----
>> From: jorge.castro at [mailto:jorge.castro at] On Behalf
>> Of Jorge O. Castro
>> Sent: Friday, August 29, 2014 10:18 AM
>> To: Humphrey, Timothy L (RIS-DAY); Marco Ceppi
>> Subject: Re: Question about the start hook
>> That's a good question! CCing in Marco, who should know.
>> On Fri, Aug 29, 2014 at 10:16 AM, Humphrey, Timothy L (RIS-DAY) <
>> Timothy.Humphrey at> wrote:
>> > Jorge,
>> >
>> > I am using juju charm to deploy to aws, an hpcc cluster, which is
>> several instances that work together to complete some job.
>> >
>> > In my start hook, I'm copying files from S3 to each instance. And, once
>> all files are copied to all instances, I perform an operation in my
>> hpcc-cluster-relation-joined that tells the master instance that all files
>> are copied to all instances.
>> >
>> > So, my question is, "Do all instances complete the start hook before
>> any instance begins the hpcc-cluster-relation-joined hook?"
>> >
>> > "Or is there a way to make this be true?"
>> >
>> > Sincerely,
>> > Tim
>> >
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