[libvirt] 1. Domain Destroy , 2. Domain boot on a different host and 3. Domain start time
Hello, Firstly, I have some confusion about the libvirt API "virDomainDestroy" method. here is the link to API: http://libvirt.org/html/libvirt-libvirt.html#virDomainDestroy Does this method completely removes the domain from the system? I have confusion because the "virsh destroy" tool option performs a forced shutdown and does not destroy/delete/remove the domain. So, what does "virDomainDestroy" method do exactly? Also, if it comletely removes the domain, then is there any other method to perform a force shutdown of the domain. I know the "virDomainShutdown" method performs a normal shutdown. Secondly, Is it possible to boot a domain on a completely different physical host with the same Hypervisor configuration? For. E.g: if I have a domain on a host 192.168.101.1 running Xen with a Domain "test" in shutdown state. If I have to start/boot the domain "test" on a different physical host, running Xen say 192.168.101.2, is it possible using libvirt API? If not, then is there any other method to do it? Thirdly, Is there a method to get the total running time of a domain? I mean, the amount of time since the domain had been booted. Currently, I can fetch the CPU time. But, is this the exact amount of time the domain is ON? i.e. If the domain is in a "IDLE" state, the CPU time does not increase. But what I want is the amount of time the domain was ON(including the idle time). So, If I can get the start time of the domain, I can calculate the duration. Sorry for the long mail and description. Any help would be greatly appreciated. Thanks and Regards Sagar Barve
On 06/17/2010 05:50 PM, IKI-サガル バルウェ wrote:
Hello,
Firstly, I have some confusion about the libvirt API "virDomainDestroy" method. here is the link to API: http://libvirt.org/html/libvirt-libvirt.html#virDomainDestroy
"Destroy" here can be a bit confusing. It doesn't really touch or remove the disk data. "Destroy" in this case means to destroy just the running instance of the domain. i.e. stop running it, free up the memory that was allocated to it, and free up any devices (network resource, etc) that had been assigned to it. If the domain has an XML definition for it in place, the "Destroy" command won't touch it. You can start the domain again using the "Create" function: http://libvirt.org/html/libvirt-libvirt.html#virDomainCreate If you want to get rid of an XML definition for the domain from a server, the command you're looking for is "undefine": http://libvirt.org/html/libvirt-libvirt.html#virDomainUndefine
Secondly, Is it possible to boot a domain on a completely different physical host with the same Hypervisor configuration? For. E.g: if I have a domain on a host 192.168.101.1 running Xen with a Domain "test" in shutdown state. If I have to start/boot the domain "test" on a different physical host, running Xen say 192.168.101.2, is it possible using libvirt API? If not, then is there any other method to do it?
You can use libvirt for this, but it's not automatic. As far as I know, you'll need to have your software connect to each of the servers and launch the appropriate virDomainCreate() (and probably other) commands. So, it would be up to your application to make sure that the domain is not running on server A, before you launch it on server B.
Thirdly, Is there a method to get the total running time of a domain? I mean, the amount of time since the domain had been booted. Currently, I can fetch the CPU time. But, is this the exact amount of time the domain is ON? i.e. If the domain is in a "IDLE" state, the CPU time does not increase. But what I want is the amount of time the domain was ON(including the idle time). So, If I can get the start time of the domain, I can calculate the duration.
Sorry, I personally can't help with this one. I haven't had to look at this stuff yet. Hope the above stuff helps though. :) Regards and best wishes, Justin Clift -- Salasaga - Open Source eLearning IDE http://www.salasaga.org
Thanks a lot Justin for such a detailed explanation.
If the domain has an XML definition for it in place, the "Destroy" command won't touch it. You can start the domain again using the "Create" function:
http://libvirt.org/html/libvirt-libvirt.html#virDomainCreate
If you want to get rid of an XML definition for the domain from a server, the command you're looking for is "undefine":
http://libvirt.org/html/libvirt-libvirt.html#virDomainUndefine
I understood now what the destroy function does. As for "domainUndefine": To quote from the "undefine" method's documentation: Undefine a domain but does not stop it if it is running So, If the Domain remains as it is, what is the significance of removing the XML Description/Definition? What I want to do, is to remove the Domain completely from the system, including its associated virtual disks. Is there any way to do this using the API?
Secondly, Is it possible to boot a domain on a completely different physical host with the same Hypervisor configuration?
You can use libvirt for this, but it's not automatic. As far as I know, you'll need to have your software connect to each of the servers and launch the appropriate virDomainCreate() (and probably other) commands. So, it would be up to your application to make sure that the domain is not running on server A, before you launch it on server B.
I am sorry, but I did not get this quite completely. Could you please explain this a bit more? Especially the "it would be up to your application to make sure that the domain is not running on server A, before you launch it on server B" part. Firstly, how will I get the domain from server A to server B to launch it there? By migrating it to server B? Please help. Thanks and Regards Sagar Barve ----- Original Message ----- From: "Justin Clift" <justin@salasaga.org> To: "IKI-サガル バルウェ" <sagar.barve@ikic.co.jp> Cc: <libvir-list@redhat.com> Sent: Thursday, June 17, 2010 5:17 PM Subject: Re: [libvirt] 1. Domain Destroy , 2. Domain boot on a different host and 3. Domain start time
On 06/17/2010 05:50 PM, IKI-サガル バルウェ wrote:
Hello,
Firstly, I have some confusion about the libvirt API "virDomainDestroy" method. here is the link to API: http://libvirt.org/html/libvirt-libvirt.html#virDomainDestroy
"Destroy" here can be a bit confusing. It doesn't really touch or remove the disk data. "Destroy" in this case means to destroy just the running instance of the domain. i.e. stop running it, free up the memory that was allocated to it, and free up any devices (network resource, etc) that had been assigned to it.
If the domain has an XML definition for it in place, the "Destroy" command won't touch it. You can start the domain again using the "Create" function:
http://libvirt.org/html/libvirt-libvirt.html#virDomainCreate
If you want to get rid of an XML definition for the domain from a server, the command you're looking for is "undefine":
http://libvirt.org/html/libvirt-libvirt.html#virDomainUndefine
Secondly, Is it possible to boot a domain on a completely different physical host with the same Hypervisor configuration? For. E.g: if I have a domain on a host 192.168.101.1 running Xen with a Domain "test" in shutdown state. If I have to start/boot the domain "test" on a different physical host, running Xen say 192.168.101.2, is it possible using libvirt API? If not, then is there any other method to do it?
You can use libvirt for this, but it's not automatic. As far as I know, you'll need to have your software connect to each of the servers and launch the appropriate virDomainCreate() (and probably other) commands. So, it would be up to your application to make sure that the domain is not running on server A, before you launch it on server B.
Thirdly, Is there a method to get the total running time of a domain? I mean, the amount of time since the domain had been booted. Currently, I can fetch the CPU time. But, is this the exact amount of time the domain is ON? i.e. If the domain is in a "IDLE" state, the CPU time does not increase. But what I want is the amount of time the domain was ON(including the idle time). So, If I can get the start time of the domain, I can calculate the duration.
Sorry, I personally can't help with this one. I haven't had to look at this stuff yet.
Hope the above stuff helps though. :)
Regards and best wishes,
Justin Clift
-- Salasaga - Open Source eLearning IDE http://www.salasaga.org
On 06/17/2010 07:04 PM, IKI-サガル バルウェ wrote: <snip>
I understood now what the destroy function does. As for "domainUndefine": To quote from the "undefine" method's documentation: Undefine a domain but does not stop it if it is running So, If the Domain remains as it is, what is the significance of removing the XML Description/Definition? What I want to do, is to remove the Domain completely from the system, including its associated virtual disks. Is there any way to do this using the API?
No worries. There's a main concept you need to get, but it's easy so keep on reading. :) With libvirt, there are two related parts: a) Domain "definition" storage (an XML file) b) Running of a definition (KVM/Xen/etc) Keeping the concept simple, the key idea is you have 2 ways of starting a brand new domain: a) starting a domain in a "transient" fashion, where the XML that describes the domain's attributes and features isn't kept around. Using this method, KVM/Xen/etc is launched with the appropriate resources, but the config for it isn't saved to disk. If you restart libvirt or the host server, then libvirtd will completely forget this domain exists. It will be gone, and you won't be able to manage it. ================================================ | Runs in memory? | Config saved to disk? | ================================================ = Yes = No = ================================================ b) starting a domain in a "persistent" fashion, where the XML that describes the domain's attributes and features IS kept around, saved to disk. Using this method, KVM/Xen/etc is launched with the appropriate resources too, plus the config for it (an XML file) is saved to disk. If you restart libvirt, then libvirt knows about this domain and you can still manage it. ================================================ | Runs in memory? | Config saved to disk? | ================================================ = Yes = Yes = ================================================ The act of saving the config file to disk, so the domain is persistent, is called "Defining" it. You can get a type a) domain above that wouldn't persist across host reboots, run a "Define" on it, then you have a type b) that will persist across reboots. Going the other way works too. If you "Undefine" a domain, that doesn't affect the running instance, but takes away the config file. The next time libvirt is restarted, the domain is unknown. http://libvirt.org/html/libvirt-libvirt.html#virDomainDefineXML http://libvirt.org/html/libvirt-libvirt.html#virDomainUndefine **************** Separate to that are the "Create" and "Destroy" functions, which control a (possibly running) instance: http://libvirt.org/html/libvirt-libvirt.html#virDomainCreate http://libvirt.org/html/libvirt-libvirt.html#virDomainDestroy These don't affect the config file saved state, they just start up or shut down KVM/Xen/etc. **************** So, with the above in mind, to completely kill off a domain you need to both: + Destroy it's instance if it's running + Undefine it's config file if it's defined Check with: http://libvirt.org/html/libvirt-libvirt.html#virDomainIsPersistent (btw - this is all a concept explanation. It's good enough to get you started. As you explore functions in the libvirt docs you will find and learn to use bits that can short cut or change this. :> )
Secondly, Is it possible to boot a domain on a completely different physical host with the same Hypervisor configuration?
You can use libvirt for this, but it's not automatic. As far as I know, you'll need to have your software connect to each of the servers and launch the appropriate virDomainCreate() (and probably other) commands. So, it would be up to your application to make sure that the domain is not running on server A, before you launch it on server B.
I am sorry, but I did not get this quite completely. Could you please explain this a bit more? Especially the "it would be up to your application to make sure that the domain is not running on server A, before you launch it on server B" part. Firstly, how will I get the domain from server A to server B to launch it there? By migrating it to server B?
Yeah, that's a more in depth explanation. I don't personally have the time at the moment to write that up. :( The short answer is that you need to make sure the storage (disk/SAN/NAS/etc) can be seen from both hosts, and that you can use your above knowledge to transfer the XML config around (if you want) and Create or Destroy or Migrate domains appropriately. Hope that helps. :) Regards and best wishes, Justin Clift
Please help.
Thanks and Regards Sagar Barve
-- Salasaga - Open Source eLearning IDE http://www.salasaga.org
Thanks Justin, Thanks for a fantastic explaination!! This clears up so many of my doubts. I will try out all this and other ways I have in mind while referring to the libvirt docs. Thanks a ton. Thanks and Regards Sagar Barve ----- Original Message ----- From: "Justin Clift" <justin@salasaga.org> To: "IKI-サガル バルウェ" <sagar.barve@ikic.co.jp> Cc: <libvir-list@redhat.com> Sent: Thursday, June 17, 2010 8:39 PM Subject: Re: [libvirt] 1. Domain Destroy , 2. Domain boot on a different host and 3. Domain start time
On 06/17/2010 07:04 PM, IKI-サガル バルウェ wrote: <snip>
I understood now what the destroy function does. As for "domainUndefine": To quote from the "undefine" method's documentation: Undefine a domain but does not stop it if it is running So, If the Domain remains as it is, what is the significance of removing the XML Description/Definition? What I want to do, is to remove the Domain completely from the system, including its associated virtual disks. Is there any way to do this using the API?
No worries. There's a main concept you need to get, but it's easy so keep on reading. :)
With libvirt, there are two related parts:
a) Domain "definition" storage (an XML file) b) Running of a definition (KVM/Xen/etc)
Keeping the concept simple, the key idea is you have 2 ways of starting a brand new domain:
a) starting a domain in a "transient" fashion, where the XML that describes the domain's attributes and features isn't kept around.
Using this method, KVM/Xen/etc is launched with the appropriate resources, but the config for it isn't saved to disk. If you restart libvirt or the host server, then libvirtd will completely forget this domain exists. It will be gone, and you won't be able to manage it.
================================================ | Runs in memory? | Config saved to disk? | ================================================ = Yes = No = ================================================
b) starting a domain in a "persistent" fashion, where the XML that describes the domain's attributes and features IS kept around, saved to disk.
Using this method, KVM/Xen/etc is launched with the appropriate resources too, plus the config for it (an XML file) is saved to disk. If you restart libvirt, then libvirt knows about this domain and you can still manage it.
================================================ | Runs in memory? | Config saved to disk? | ================================================ = Yes = Yes = ================================================
The act of saving the config file to disk, so the domain is persistent, is called "Defining" it. You can get a type a) domain above that wouldn't persist across host reboots, run a "Define" on it, then you have a type b) that will persist across reboots.
Going the other way works too. If you "Undefine" a domain, that doesn't affect the running instance, but takes away the config file. The next time libvirt is restarted, the domain is unknown.
http://libvirt.org/html/libvirt-libvirt.html#virDomainDefineXML http://libvirt.org/html/libvirt-libvirt.html#virDomainUndefine
****************
Separate to that are the "Create" and "Destroy" functions, which control a (possibly running) instance:
http://libvirt.org/html/libvirt-libvirt.html#virDomainCreate http://libvirt.org/html/libvirt-libvirt.html#virDomainDestroy
These don't affect the config file saved state, they just start up or shut down KVM/Xen/etc.
****************
So, with the above in mind, to completely kill off a domain you need to both:
+ Destroy it's instance if it's running + Undefine it's config file if it's defined
Check with: http://libvirt.org/html/libvirt-libvirt.html#virDomainIsPersistent
(btw - this is all a concept explanation. It's good enough to get you started. As you explore functions in the libvirt docs you will find and learn to use bits that can short cut or change this. :> )
Secondly, Is it possible to boot a domain on a completely different physical host with the same Hypervisor configuration?
You can use libvirt for this, but it's not automatic. As far as I know, you'll need to have your software connect to each of the servers and launch the appropriate virDomainCreate() (and probably other) commands. So, it would be up to your application to make sure that the domain is not running on server A, before you launch it on server B.
I am sorry, but I did not get this quite completely. Could you please explain this a bit more? Especially the "it would be up to your application to make sure that the domain is not running on server A, before you launch it on server B" part. Firstly, how will I get the domain from server A to server B to launch it there? By migrating it to server B?
Yeah, that's a more in depth explanation. I don't personally have the time at the moment to write that up. :(
The short answer is that you need to make sure the storage (disk/SAN/NAS/etc) can be seen from both hosts, and that you can use your above knowledge to transfer the XML config around (if you want) and Create or Destroy or Migrate domains appropriately.
Hope that helps. :)
Regards and best wishes,
Justin Clift
Please help.
Thanks and Regards Sagar Barve
-- Salasaga - Open Source eLearning IDE http://www.salasaga.org
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IKI-サガル バルウェ -
Justin Clift