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Re: [Xen-users] how to start VMs in a particular order

  • To: xen-users@xxxxxxxxxxxxx
  • From: "J. Roeleveld" <joost@xxxxxxxxxxxx>
  • Date: Sun, 29 Jun 2014 15:19:14 +0200
  • Delivery-date: Sun, 29 Jun 2014 13:20:57 +0000
  • List-id: Xen user discussion <xen-users.lists.xen.org>

On Saturday, June 28, 2014 03:06:18 PM squidmobile@xxxxxxxxxxx wrote:
> 28 jun 2014
> greetings,
> > Is this a feature, or did you happen to create the links in the desired
> > order?  I see both possibilities, i. e. sorting the directory entries as
> > a feature, or start the VMs in the order the files/links have been
> > created/are found as directory entries.
> i use jfs, which happens to have (what i think is) the beautiful
> characteristic of always listing files in alphabetic sequence.  no
> piping through sort or anything else.

For completeness, this has nothing to do with the filesystem used.

<snipped example>

> > In this case, the VM with the name server
> > needs to be up first, then the VM with the firewall, then the VM with
> > the NFS server and finally the rest of them in no particular order.
> hmmm.  can some of these come up in parallel?  does the firewall
> use ip addresses from the dns server, or does it hard code them?
> does the firewall separate the nfs server from the dns server?
> granted, the lack of dns affects the nfs clients, but wouldn't the
> nfs server (mostly) ignore dns until it finished booting and began
> nfs operations?

Not entirely certain, but I believe the /etc/exports file is parsed upon start 
of the service. At which point does it resolve the hostnames listed there?

> > How do you find out whether a VM is fully up or not even within the very
> > same VM?
> well, dom0 can maintain a log of vm console output (i forget
> exactly where, but i think somewhere under /var/log/xen/console).

For this, the use of screen for the domU console is necessary.

> tweak your vm startup scripts to echo something like "start the
> next vm" and let the dom0 auto script wait for the signal before xl
> create the next vm.  put a sleep 5 in the auto script to keep it
> from thrashing.  would some variant of this work for you?

Waiting for the login-prompt would work. Sending a message using a TCP-
connection from the domU to something running on dom0 would also be an option.


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