[ovirt-devel] Libvirt secrets management - take 2

[Oved Ourfali]

On Jun 12, 2015 14:21, Nir Soffer <nsoffer at redhat.com> wrote:
>
> Hi all, 
>
> Recently support for Ceph network disk landed in master. It its possible 
> now to start a vm using Ceph network disk or hot-plug/unplug such disk 
> using Cephx authentication. 
>
> However, to make it work, you must add the relevant Ceph secret to 
> libvirt manually, in the same way it is done in OpenStack deployment. 
> Our goal is to manage secrets automatically and use ephemeral (safer) 
> secrets. 
>
> The next patches in the Ceph topic [1], implement secret management in 
> the same way we manage storage domains or server connections: 
>
> The concept is - all hosts can use all secrets, so you can migrate a vm 
> using Ceph disk to any host in the cluster. 
>
> 1. When host becomes up, we register the secrets associated with all the 
>    current active domains with libvirt 
>
> 2. When activating a domain, we register the secrets associated with the 
>    new domain with libvirt 
>
> 3. When deactivating a domain, we unregister the secrets associated with 
>    the domain from libvirt 
>
> 4. When moving host to maintenance, we clear all secrets 
>
> 5. When vdsm shutdown or starts, clear all secrets to ensure that we don't keep 
>    stale or unneeded secrets on a host 
>
> This system seems to work, but Federico pointed few issues and suggested 
> a new (simpler?) approach. 
>
> In future libvirt version, libvirt will support the concept of transient 
> secrets so you can start a transient vm using secret without registering 
> the secret with libvirt before starting the vm. The secret will be 
> specified in the vm XML (for starting a vm) or disk XML (for hot-plug). 
> This will make our secret management system and APIs useless. 

When is this planned to be added to libvirt? iiuc, once added, you will no longer need to register the secrets with libvirt, right? 

>
> Managing state on multiple hosts is hard; we will probably have to deal 
> with nasty edge cases (e.g. lost messages, network errors), which may 
> lead to host with missing secret, which cannot run some vms. We probably 
> do this right for storage domains (after 8 years?), and we should not 
> assume that we are smarter and secret management will work in the first 
> try. 
>
> The new approach is to *not* manage state or multiple hosts. Instead, 
> send the required secrets only to the host that starting a vm or 
> hot-plugging a disk that need a libvirt secret: 
>
> 1. When starting a vm, add the required secrets to the vm description. 
>    On the host, vdsm will register these secrets with libvirt before 
>    starting the vm. 
>
> 2. When migrating a vm, add the required secrets to the vm description. 
>    On the host, vdsm will send these secrets to the destination host, 
>    and on the destination host, vdsm will register the secrets with libvirt 
>    before starting the vm. 
>

Will these secrets be part of the domain xml? 
If so, no need for special treatment in case of VM migration. 

> 3. When hot-plugging a disk, send the secret if needed in the disk 
>    description.  On the host, vdsm will register the secrets with libvirt. 
>
> 4. When vdsm shutdown or starts, clear all secrets to ensure that we don't keep 
>    stale or unneeded secrets on a host 
>
> 5. We never unregister secrets, since they are ephemeral anyway. 
>
> 6. Alternatively, we can implement secrets reference counting so when a vm 
>    stops or disk is hot-unplugged we decrease the reference count on the 
>    secrets associated with this vm/disk, and if no other vms need the 
>    secret, we can unregister the secret from libvirt. 

Doesn't seem necessary to me. 

>
> The new approach is simpler, if we avoid the fancy secret reference 
> counting. I believe we can get it merged in couple of weeks with help 
> from the virt team.
>
> Please share your thoughts on these alternative solutions. 
>

Keep in mind also hosted engine. Sounds to me like the new approach will be a better fit for it, as he won't need to deal with storage domain secrets, but just pass it in the VM description... Although I'm not a hosted engine expert, so not sure it makes a difference, but it sounds simpler in that aspect as well. 


> Thanks, 
> Nir 
>
> [1] https://gerrit.ovirt.org/#/q/status:open+project:vdsm+branch:master+topic:ceph 
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