On Sun, Dec 4, 2016 at 10:39 PM, Yaniv Kaul <ykaul(a)redhat.com&gt; wrote: ​A VM. It is not safe to modify template disks. We cannot guarantee that there are no VMs based on this template, because some of them may reside on a detached storage.​ ​Shmuel​

On Sun, Dec 4, 2016 at 8:50 PM, Shmuel Melamud <smelamud(a)redhat.com&gt; wrote: New storage verbs are volume based. This make it easy to manage them on the engine side, and will allow parallelizing volume operations on single or multiple hosts. A storage volume job is using sanlock lease on the modified volume and volume generation number. If a host running pending jobs becomes non-responsive and cannot be fenced, we can detect the state of the job, fence the job, and start the job on another host. In the SPM task, if a host becomes non-responsive and cannot be fenced, the whole setup is stuck, there is no way to perform any storage operation. We can do: 1. Add jobs with multiple volumes leases - can make error handling very complex. How do tell a job state if you have multiple leases? which volume generation you use? 2. Use volume job using one of the volumes (the boot volume?). This does not protect the other volumes from modification but engine is responsible for this. 3. Use new "vm jobs", using a vm lease (should be available this week on master). This protects a vm during sysprep from starting the vm. We still need a generation to detect the job state, I think we can use the sanlock lease generation for this. I like the last option since sysprep is much like running a vm. It does not. v2v predates storage volume jobs. It does not use volume leases and generation and does have any way to recover if a host running v2v becomes non-responsive and cannot be fenced. It also does not use the jobs framework and does not use a thread pool for v2v jobs, so it has no limit on the number of storage operations on a host. Nir

On Mon, Dec 5, 2016 at 10:05 AM, Nir Soffer <nsoffer(a)redhat.com&gt; wrote: Right, but let's be fair and present the benefits of v2v-jobs as well: 1. it is the simplest "infrastructure" in terms of LOC 2. it is the most efficient mechanism in terms of interactions between the engine and VDSM (it doesn't require new verbs/call, the data is attached to VdsStats; probably the easiest mechanism to convert to events) 3. it is the most efficient implementation in terms of interaction with the database (no date is persisted into the database, no polling is done) Currently we have 3 mechanisms to report jobs: 1. VM jobs - that is currently used for live-merge. This requires the VM entity to exist in VDSM, thus not suitable for virt-sysprep. 2. storage jobs - complicated infrastructure, targeted for recovering from failures to maintain storage consistency. Many of the things this infrastructure knows to handle is irrelevant for virt-sysprep flow, and the fact that virt-sysprep is invoked on VM rather than particular disk makes it less suitable. 3. V2V jobs - no mechanism is provided to resume failed jobs, no leases, etc I have some arguments for using V2V-like jobs [1]: 1. creating template from vm is rarely done - if host goes unresponsive or any other failure is detected we can just remove the template and report the error 2. the phase of virt-sysprep is, unlike typical storage operation, short - reducing the risk of failures during the process 3. during the operation the VM is down - by locking the VM/template and its disks on the engine side, we render leases-like mechanism redundant 4. in the worst case - the disk will not be corrupted (only some of the data might be removed). So I think that the mechanism for storage jobs is an over-kill for this case. We can keep it simple by generalise the V2V-job for other virt-tools jobs, like virt-sysprep. [1] I believe that as Moran and Yaniv noted, we can just do it in the create template flow without the intermediate (POC) stage of having an operation for doing that on existing VM or template - it only complicates stuff Nir

Arik Hadas <ahadas(a)redhat.com&gt; writes: Nice summary. Based on the arguments you provide the v2v-like way looks like a good solution. Providing we can attach the operation to the create template flow it should be safe and simple. These two don't look like options worth to bother with. If we can perform virt-sysprep within the create template flow, does this option provide any real benefit over what Arik suggests? Would it simplify things or add complexity to the proposed solution?

Adam, Just out of curiosity: when you write "v2v has promised" - what exactly do you mean? the tool? Richard Jones (the maintainer of virt-v2v)? Shahar and I that implemented the integration with virt-v2v? I'm not aware of such a promise by any of these options :) Anyway, let's say that you were given such a promise by someone and thus consider that mechanism to be deprecated - it doesn't really matter. The current implementation doesn't well fit to this flow (it requires per-volume job, it creates leases that are not needed for template's disks, ...) and with the "next-gen API" with proper support for virt flows not even being discussed with us (and iiuc also not with the infra team) yet, I don't understand what do you suggest except for some strong, though irrelevant, statements. I suggest loud and clear to reuse (not to add dependencies, not to enhance, ..) an existing mechanism for a very similar flow of virt-v2v that works well and simple. Do you "promise" to implement your "next gen API" for 4.1 as an alternative? On Tue, Dec 6, 2016 at 5:04 PM, Adam Litke <alitke(a)redhat.com&gt; wrote:

On Tue, Dec 6, 2016 at 11:12 PM, Adam Litke <alitke(a)redhat.com&gt; wrote: Well, I think that when someone builds a good infrastructure he first needs to talk to all consumers and make sure it fits. In this case it seems like most work was done to fit the storage use-case, and now you check whether it can fit others as well.... IMO it makes much more sense to use events where possible (and you've promised to use those as well, but I don't see you doing that...). v2v should use events for sure, and they have promised to do that in the past, instead of using the v2v jobs. The reason events weren't used originally with the v2v feature, was that it was too risky and the events infrastructure was added too late in the game.

On Dec 7, 2016 16:00, "Nir Soffer" <nsoffer(a)redhat.com&gt; wrote: exactly and I thus not irrelevant, then well list, had. The core team was there. So it is surprising. > >> >> Of course plans can change but I have never been looped into any such > >> discussions. > >> > > Well, I think that when someone builds a good infrastructure he first needs use-case, > > and now you check whether it can fit others as well.... > The jobs framework is generic and can be used for any subsystem, > there is nothing related to storage about it. But modifying disks *is* > a storage operation, even if someone from the virt team worked on it. > V2v is also storage operation - if we compare it with copying disks: > - we create a new volume that nobody is using yet > - if the operation fails, the disk must be in illegal state > - if the operation fails we delete the disks > - if the operation succeeds the volume must be legal > - we need to limit the number of operations on a host > - we need to detect the job state if the host becomes non-responsive > - we may want to fence the job if the host becomes non-responsive > in volume jobs, we can increment the volume generation and run > the same job on another host. > - we want to take a lease on storage to ensure that other hosts cannot > access the same entity, or that the job will fail if someone else is using > this entity > - we want to take a lease on storage, ensuring that a job cannot get > stuck for long time - sanlock kill the owner of a lease when storage > becomes inaccessible. > - we want to report progress > sysprep is less risky because the operation is faster, but on storage even > fast operation can get stuck for minutes. > We need to agree on a standard way to do such operations that is safe enough > and can be managed on the engine side. > > IMO it makes much more sense to use events where possible (and you've > > promised to use those as well, but I don't see you doing that...). v2v > > should use events for sure, and they have promised to do that in the past, > > instead of using the v2v jobs. The reason events weren't used originally > > with the v2v feature, was that it was too risky and the events > > infrastructure was added too late in the game. > Events are not replacing the need for managing jobs in the vdsm side. > Engine must have a way to query the current jobs before subscribing > to events from these jobs, otherwise you will loose events and engine > will never notice a completed job after network errors. > The jobs framework supports events, see > https://gerrit.ovirt.org/67118 > We are waiting for review from the infra team, maybe you can > get someone to review this? It would have been great to review the design for this before it reaches to gerrit. Anyway, I get permissions error when opening. Any clue why? > Nir > > > >>> >>> Do you "promise" to implement your "next gen API" for 4.1 as an > >>> alternative? > >> >> >> I guess we need the design first. > >> >> >>> On Tue, Dec 6, 2016 at 5:04 PM, Adam Litke <alitke(a)redhat.com&gt; wrote: > >>> >>> On 05/12/16 11:17 +0200, Arik Hadas wrote: > >>> >>> >>> >>> On Mon, Dec 5, 2016 at 10:05 AM, Nir Soffer <nsoffer(a)redhat.com > >>> wrote: > >>> >>> On Sun, Dec 4, 2016 at 8:50 PM, Shmuel Melamud > >>> <smelamud(a)redhat.com> >>> wrote: > >>> > >>> > Hi! > >>> > >>> > I'm currently working on integration of virt-sysprep into > >>> oVirt. > >>> > >>> > Usually, if user creates a template from a regular VM, and > >>> then > >>> creates > >>> new VMs from this template, these new VMs inherit all > >>> configuration > >>> of the > >>> original VM, including SSH keys, UDEV rules, MAC addresses, > >>> system > >>> ID, > >>> hostname etc. It is unfortunate, because you cannot have two > >>> network > >>> devices with the same MAC address in the same network, for > >>> example. > >>> > >>> > To avoid this, user must clean all machine-specific > >>> configuration > >>> from > >>> the original VM before creating a template from it. You can do > >>> this > >>> manually, but there is virt-sysprep utility that does this > >>> automatically. > >>> > >>> > Ideally, virt-sysprep should be seamlessly integrated into > >>> template > >>> creation process. But the first step is to create a simple > >>> button: > >>> user > >>> selects a VM, clicks the button and oVirt executes virt-sysprep > >>> on > >>> the VM. > >>> > >>> > virt-sysprep works directly on VM's filesystem. It accepts > >>> list of > >>> all > >>> disks of the VM as parameters: > >>> > >>> > virt-sysprep -a disk1.img -a disk2.img -a disk3.img > >>> > >>> > The architecture is as follows: command on the Engine side > >>> runs a > >>> job on > >>> VDSM side and tracks its success/failure. The job on VDSM side > >>> runs > >>> virt-sysprep. > >>> > >>> > The question is how to implement the job correctly? > >>> > >>> > I thought about using storage jobs, but they are designed to > >>> work > >>> only > >>> with a single volume, correct? > >>> >>> New storage verbs are volume based. This make it easy to manage > >>> them on the engine side, and will allow parallelizing volume > >>> operations > >>> on single or multiple hosts. > >>> >>> A storage volume job is using sanlock lease on the modified > >>> volume > >>> and volume generation number. If a host running pending jobs > >>> becomes > >>> non-responsive and cannot be fenced, we can detect the state of > >>> the job, fence the job, and start the job on another host. > >>> >>> In the SPM task, if a host becomes non-responsive and cannot be performed > >>> on > >>> multiple > >>> volumes? > >>> > Or, alternatively, is it possible to use some kind of 'VM > >>> jobs' - > >>> that > >>> work on VM at whole? > >>> >>> We can do: > >>> >>> 1. Add jobs with multiple volumes leases - can make error > >>> handling > >>> very > >>> complex. How do tell a job state if you have multiple > >>> leases? > >>> which > >>> volume generation you use? > >>> >>> 2. Use volume job using one of the volumes (the boot volume?). engine > >>> is > >>> responsible > >>> for this. > >>> >>> 3. Use new "vm jobs", using a vm lease (should be available > >>> this > >>> week > >>> on master). > >>> This protects a vm during sysprep from starting the vm. > >>> We still need a generation to detect the job state, I think > >>> we > >>> can > >>> use the sanlock > >>> lease generation for this. > >>> >>> I like the last option since sysprep is much like running a vm. > >>> > How v2v solves this problem? > >>> >>> It does not. > >>> >>> v2v predates storage volume jobs. It does not use volume leases becomes > >>> non-responsive > >>> and cannot be fenced. > >>> >>> It also does not use the jobs framework and does not use a > >>> thread > >>> pool for > >>> v2v jobs, so it has no limit on the number of storage > >>> operations on > >>> a host. > >>> >>> >>> Right, but let's be fair and present the benefits of v2v-jobs as > >>> well: > >>> 1. it is the simplest "infrastructure" in terms of LOC > >>> >>> >>> It is also deprecated. V2V has promised to adopt the richer Host Jobs > >>> API in the future. > >>> >>> >>> 2. it is the most efficient mechanism in terms of interactions > >>> between > >>> the > >>> engine and VDSM (it doesn't require new verbs/call, the data is > >>> attached to > >>> VdsStats; probably the easiest mechanism to convert to events) > >>> >>> >>> Engine is already polling the host jobs API so I am not sure I agree > >>> with you here. > >>> >>> >>> 3. it is the most efficient implementation in terms of interaction > >>> with > >>> the > >>> database (no date is persisted into the database, no polling is > >>> done) > >>> >>> >>> Again, we're already using the Host Jobs API. We'll gain efficiency > >>> by migrating away from the old v2v API and having a single, unified > >>> approach (Host Jobs). > >>> >>> >>> Currently we have 3 mechanisms to report jobs: > >>> 1. VM jobs - that is currently used for live-merge. This requires > >>> the > >>> VM entity > >>> to exist in VDSM, thus not suitable for virt-sysprep. > >>> >>> >>> Correct, not appropriate for this application. > >>> >>> >>> 2. storage jobs - complicated infrastructure, targeted for > >>> recovering > >>> from > >>> failures to maintain storage consistency. Many of the things this > >>> infrastructure knows to handle is irrelevant for virt-sysprep > >>> flow, and > >>> the > >>> fact that virt-sysprep is invoked on VM rather than particular > >>> disk > >>> makes it > >>> less suitable. > >>> >>> >>> These are more appropriately called HostJobs and the have the > >>> following semantics: > >>> - They represent an external process running on a single host > >>> - They are not persisted. If the host or vdsm restarts, the job is > >>> aborted > >>> - They operate on entities. Currently storage is the first adopter > >>> of the infrastructure but virt was going to adopt these for the > >>> next-gen API. Entities can be volumes, storage domains, vms, > >>> network interfaces, etc. > >>> - Job status and progress is reported by the Host Jobs API. If a job > >>> is not present, then the underlying entitie(s) must be polled by > >>> engine to determine the actual state. > >>> >>> >>> 3. V2V jobs - no mechanism is provided to resume failed jobs, no > >>> leases, etc > >>> >>> >>> This is the old infra upon which Host Jobs are built. v2v has > >>> promised to move to Host Jobs in the future so we should not add new > >>> dependencies to this code. > >>> >>> >>> I have some arguments for using V2V-like jobs [1]: > >>> 1. creating template from vm is rarely done - if host goes > >>> unresponsive > >>> or any > >>> other failure is detected we can just remove the template and > >>> report > >>> the error > >>> >>> >>> We can chose this error handling with Host Jobs as well. > >>> >>> >>> 2. the phase of virt-sysprep is, unlike typical storage operation, > >>> short - > >>> reducing the risk of failures during the process > >>> >>> >>> Reduced risk of failures is never an excuse to have lax error > >>> handling. The storage flavored host jobs provide tons of utilities > >>> for making error handling standardized, easy to implement, and > >>> correct. > >>> >>> >>> 3. during the operation the VM is down - by locking the > >>> VM/template and > >>> its > >>> disks on the engine side, we render leases-like mechanism > >>> redundant > >>> >>> >>> Eventually we want to protect all operations on storage with sanlock to requires outweigh > >>> any perceived simplification resulting from omitting it. > >>> >>> >>> 4. in the worst case - the disk will not be corrupted (only some > >>> of the > >>> data > >>> might be removed). > >>> >>> >>> Again, the way engine chooses to handle job failures is independent of > >>> the mechanism. Let's separate that from this discussion. > >>> >>> >>> So I think that the mechanism for storage jobs is an over-kill for > >>> this > >>> case. > >>> We can keep it simple by generalise the V2V-job for other > >>> virt-tools > >>> jobs, like > >>> virt-sysprep. > >>> >>> >>> I think we ought to standardize on the Host Jobs framework where we > >>> can collaborate on unit tests, standardized locking and error > >>> handling, abort logic, etc. When v2v moves to host jobs then we will > >>> have a unified method of handling ephemeral jobs that are tied to > >>> entities. > >>> >>> -- > >>> Adam Litke > >>> >>> >> >> -- > >> Adam Litke > >

On Dec 7, 2016 20:16, "Nir Soffer" <nsoffer(a)redhat.com&gt; wrote: wrote: wrote: and the for opportunity. matter. requires template's yet, I am demand appropriate works such even v2v originally reaches to Yes. I see Piotr is already on it. I'll also be happy to hear how are you going to use events in your current design. Also, is there a design page for this work? Thanks, Oved wrote: into and addresses, two for can this into simple accepts side designed volume modified jobs state host. cannot perform 'VM available vm. running a a v2v-jobs Host interactions data is events) polling is unified virt-sysprep particular job is adopter the a by jobs, and utilities approach independent over-kill where we to

On Wed, Dec 7, 2016 at 8:24 PM, Michal Skrivanek <mskrivan(a)redhat.com&gt; wrote: On the vdsm side we don't need to rewrite the interesting parts, just run the code using the current infrastructure. The first step is to use the jobs framework and delete the stale copy of the jobs framework in v2v.py. Then we can easily schedule the jobs in the task manager instead of starting a thread for each job - one line to schedule a job in hsm - see the sparsify patch. I think Shahar started to work on it, we need to rebase his patch and finish it.