Re: [MirageOS-devel] Lifecycle

[Nik Sultana <ns441@xxxxxxxxx>]

I wonder if there's a mature interface for life-cycling lightweight 
processes in the Erlang ecosystem, perhaps covering the variety of 
phases you described originally. (I'm thinking of Erlang and lightweight 
processes since the lifecycle phases in the interface developed for such 
processes might be more germane for unikernels running microservices 
than, say, for more heavyweight VMs.)
Erlang is particularly known for its lightweight processes and 
supervision-based monitoring model. IIRC at its simplest, this model 
involves supervisors restarting processes when they die, but perhaps a 
more sophisticated coordination model has been developed for some 
use-cases.
This project comes to mind:
  http://www.release-project.eu/
How is the use-case you describe currently dealt with?

On 2016-07-14 17:22, Nick Betteridge wrote:
> > > > > > > The basic calls would be Start, Stop, Pause, Resume. Restart?
> > > > > > I suspect restart may be difficult to distinguish in certain
> > > > > > contexts, this would make it an unreliable event. Do you have any
> > > > > > particular use cas for something you'd like to do knowing that you
> > > > > > are going to restart ?
> > > > > ...in particular I wonder what Restart and Pause/Resume look like 
> > > > > in a
> > > > > unikernel / microservice world, and how are they different from
> > > > > Stop...Start. (Assuming immutability, compile-time configuration,
> > > > > state persistence into Irmin, and so on.)
> > > > Micromanagement interface? :)
> > > I guess the use-case I had in mind was the radio modem connected to 
> > > the
> > > unikernel:
> > >
> > > Stop -> inform participating unikernels that we're stopping, 
> > > housekeep,
> > > turn off the radio.
> > > Pause -> housekeep, turn off the radio
> > > Restart -> housekeep
> > >
> > > Certainly 'Stop' is a must-have.
> > Ah-- I guess I don't understand who's invoking which operation :)
> >
> > I had assumed that Start/Stop were operations that could be invoked on
> > a unikernel to boot it and then cleanly shut it down. But from what
> > you say above it sounds like Stop is a message that a unikernel may
> > broadcast to other unikernels to say "I'm stopping"? (I may just be
> > completely misunderstanding though!)
> No, no - you're quite right. Whatever is controlling the unikernel
> passes on up-coming states to the unikernel, on starting, on stopping
> etc.. It's then up to the unikernel to act on being told that 'we're
> shutting you down, buddy: STOP' via mirageos/platform etc..
>
> I guess this would be done via vchan, in the case of xen, and there 
> must
> be something similar for kvm?
>
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