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Re: [Xen-users] domU dependency-aware xendomains init script?



Nico,

Is there a smarter xendomains script out there that deals with domU dependencies better than the one in the RPMs (CentOS)? For example, directory services (eg. LDAP, DNS) are on one domU, and other domUs depend on those services to boot correctly. (Best to solve this with redundant services, yes, but let's say this is a test network.) An even stranger example is a domU whose root boots from an NFS, iSCSI or AoE filesystem on another domU.
That's not a Xen issue: that's an OS issue. As such, the init scripts of the other DomU's could perform a number of checks to see if the services are enabled yet [...]
Yes, you're right, and I didn't explain my idea clearly.

When I wrote 'smarter', I really meant something like the following: an administrator knows that the directory server must be booted first and others later. In a config file somewhere referenced by the xendomains init script, probably the same one below that configures per-domU settings for shutdown, he inserts the option to, for example, boot the dir. server immediately, and then wait 30 seconds to boot the remaining servers. This is a simple example, and there are probably use cases where more expression of more complex dependencies would be desirable.
It would also be nice, for example, to have per-domU settings for shutdown (hibernate or init 0?).

This idea is still in a seed stage, so I'm not expressing it very clearly. Any pointers to similar-sounding information, though, are well appreciated. Thanks-
Well, there you'd have to get into the "xendomain" init script that RedHat uses. It's an interesting idea: the information could theoretically be contained in a standard Xen init script, and even reported to the Xen configurations for migration. But in the short term, a sinple text-file with domain names and shutdown states could be stuffed in /etc/sysconfig/ or /etx/xen/ for exactly this sort of use.

So yes, the xendomains init script is where this work would have to be done. The RH xendomains script, and the one shipped with the xensource-provided RPMs, are the same IIRC, and both simply fire up all configs that exist in /etc/xen/auto (smart enough, at least, to wait a few seconds between successive fire-upings).

For now, I am also tempted to stick things into an /etc/sysconfig file or perhaps to set variables in the /etc/xen/config scripts. This is just a hack for now, though, and there is probably a smarter way to integrate this information into the Xen system somewhere.

   John


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