Re: [nova] How to move on from live_migration_uri?

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Re: [nova] How to move on from live_migration_uri?

Chris Friesen
On 06/07/2017 09:20 AM, Matt Riedemann wrote:

> What I'm trying to do is continue to use ssh as the scheme since that's what
> devstack sets up. So I set live_migration_scheme=ssh.
> Within the libvirt driver, it starts with a URL like this for qemu:
> qemu+%s://%s/system
> And does a string replace on that URL with (scheme, destination), which would
> give us:
> qemu+ssh://<dest>/system
> The problem lies in the dest part. Devstack is trying to specify the username
> for the ssh URI, so it wants "stack@%s" for the dest part. I tried setting
> live_migration_inbound_addr="stack@%s" but that doesn't work because the driver
> doesn't replace the dest on top of that again, so we just end up with this:
> qemu+ssh://stack@%s/system
> Is there some other way to be doing this? We could try to use tunneling but the
> config option help text for live_migration_tunnelled makes that sound scary,
> e.g. "Enable this option will definitely
> impact performance massively." Holy crap Scoobs, let's scram!

In my testing tunneling really only makes a big difference if you've got 10G
links, and even then it'll hit about 70% of the line rate for an unencrypted
tunnel (with libvirtd running at ~70% cpu util).

> Should we check if the scheme is ssh and try a final string replacement with the
> destination host after we've already applied (live_migration_scheme,
> live_migration_inbound_addr)?

Something like that seems reasonable.  It'd be nice if we didn't need an
explicit username config option.


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