and cons, and usage scenarios Jia Zeng zengjia@awcloud.com Dongcan - - PowerPoint PPT Presentation

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Jia Zeng – zengjia@awcloud.com Dongcan Ye – yedongcan@awcloud.com

Several ways to create a virtual machine image, pros and cons, and usage scenarios

CONTENTS

Background

02

Methods of creating instance image

03

Pros and Cons

04

Operation demonstration

01 05

Usage scenarios Discussion

06

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Background

In OpenStack, Glance service provide OS images for instance. Some users wants to save instance(running or not) as images. From end-user doubt :

• 1. How to create images based
• n instance?
• 2. Which way is better?
• 3. How to use those methods

for different scenarios? Create images based

• n instance

slow take space ......

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Methods for instance to create images

From Nova side： # nova image-create <server> <name> From Cinder side： # cinder upload-to-image <volume> <image-name> There are two methods for instance to create image:

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Methods for instance to create images

• 1. Call Nova API createImage
• 2. Determine instance is

volume backend or not

• 3. If volume backend instance,

call Cinder snapshot interface

• 4. Otherwise call Nova libvirt

driver to live snapshot or cold snapshot

Nova createImage API is_volume_bac kend_instance call Nova snapshot call Cinder snapshot

NO YES

snapshot upload to Glance，create mapping info create snapshot mapping update Glance DB

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Methods for instance to create images

(1) non-volume backend instance

• An instance’s root disk copy，

then upload to Glance.

• cold/live snapshot
• direct_snapshot for RBD, if

direct_snapshot not support or failed, do standard snapshot.

• direct_snapshot
• snapshot the root disk and

clone it into Ceph Glance's pool

• flatten the osd image
• after all done with the

source snapshot, clean it up

• makes a protected snapshot

called 'snap' on uploaded images

snapshot suspend instance check requirement for live snapshot No blockJobAbort create snapshot Yes Create snapshot resume instance Thaw filesystems Freeze filesystems

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Methods for instance to create images

(2) volume backend instance

• Freeze the guest filesystems(QGA supported)
• Call Cinder API to create snapshot
• Thaw the guest filesystems
• Update Glance image meta and snapshot

mapping This is the most common scenario snapshot_volume_backed Quiesce instance Cinder create_snapshot_force Unquiesce instance Update Glance image meta and snapshot mapping

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Methods for instance to create images

• 2. From Cinder side

Upload volume to Glance, we can specify disk-format for the new image:

• qcow2: upload quickly and take less

space

• raw: upload slowly and take more

space copy_volume_to_image:

• _attach_volume
• RBD: rbd export

Cinder volume_upload_image API call Glance create image info copy_volume_to_image get volume info, convert to qcow2 upload volume to Glance, update image info disk- format is RAW? not convert No Yes

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Pros and Cons

Interface description Pros Cons nova image-create Create snapshot for root disk, upload to Glance image

• upload fast
• Freeze the guest

filesystems, can make data consistency The new image may relay on the root disk and snapshot cinder upload-to- image --disk qcow2 Convert the disk to qcow2, then upload to Glance image

• upload fast
• take up less space
• has no relationship

with original root disk

• Cinder will not

freeze the disk cinder upload-to- image

• -disk raw

Directly upload the disk to Glance image

• After convert to raw

image, create instance will be faster

• upload slow
• take up more

space

• Cinder will not

freeze the disk

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Usage scenarios

• 1. Nova image-create
• For the instance boot from image, we can produce image for the instance, this is

uncommon case.

• For the instance boot from volume, if user wants to produce image quickly, and finally no

need to delete root disk and snapshot, this is common case.

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Usage scenarios

• 2. Cinder upload-to-image
• Upload disk(root disk) to Glance with qcow format, this is common case. We can delete the
• riginal disk, and uploads quickly.
• Upload disk(root disk) to Glance with raw format, this is also common case. If user has no

requirement for the speed, we can use this way. As we know, create instance with the raw image will quicker than others.(For RBD driver)

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Operation demonstration

Create volume backend VM: # nova boot volume-vm --flavor 4d360a12-991a-4e08-bd1b-3bab987353bd --nic net- id=e44c3bac-6fea-4b04-8680-30e60d2e4aa1 --block-device id=f0a7da4d-2c70-47eb-a67a- 71a04d6678de,source=image,dest=volume,size=100,bootindex=0 Create local VM: # nova boot local-vm --flavor 4d360a12-991a-4e08-bd1b-3bab987353bd --nic net- id=e44c3bac-6fea-4b04-8680-30e60d2e4aa1 --block-device id=f0a7da4d-2c70-47eb-a67a- 71a04d6678de,source=image,dest=local,size=20,bootindex=0 Nova side create image: # nova image-create SERVER IMAGE-NAME Cinder side create image: # cinder upload-to-image --force True --disk-format raw VOLUME-ID IMAGE-NAME # cinder upload-to-image --force True --disk-format qcow2 VOLUME-ID IMAGE-NAME

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Discussion

Optimization for Cinder upload-to-image

• 1. https://blueprints.launchpad.net/cinder/+spec/optimze-rbd-copy-volume-to-image

Not implemented yet, for the RBD driver. Cinder and Glance both has Ceph RBD backend, use volume copy function instead of rbd export.

• 2. https://review.opendev.org/#/c/668943

While uploading volume to Glance, if disk-format is qcow2, compress images with command ”qemu-img convert –c”

• 3. https://review.opendev.org/#/c/668825/

Leverage hardware accelerator to do the image compression. The only accelerator supported in Train release is Intel QuickAssist Technology (QAT)

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THANKS!