step by step - reusing old features to build new ones
TRANSCRIPT
DevConfCZ, Feb 2015
Step by StepReusing old features to build new ones
Allon [email protected] / @mureinikSupervisor, RHEV StorageRed HatDevConfCZ, Feb 2015
DevConfCZ, Feb 2015
Old school software development
Requirements
Design
Implementation
Verification
Maintenance
DevConfCZ, Feb 2015
And when you're all set and done
DevConfCZ, Feb 2015
An alternative approach
DevConfCZ, Feb 2015
Case study – oVirt Live Merge
DevConfCZ, Feb 2015
What Is oVirt?
Large scale, centralized management for server and desktop virtualization
Based on leading performance, scalability and security infrastructure technologies
Provide an open source alternative to vCenter/vSphere
Focus on KVM for best integration/performance
Focus on ease of use/deployment
DevConfCZ, Feb 2015
oVirt: Not a Single Project
● oVirt-Engine● VDSM● oVirt-Node● ovirt-Engine-SDK● oVirt-Engine-CLI● oVirt-Guest-Agent● oVirt-Image-Uploader● oVirt-iso-Uploader● oVirt-Log-Collector● oVirt-DWH● oVirt-Reports
● Incubation Projects– MOM– moVirt
● Test Projects
● … your contributions are welcome!
● See http://ovirt.org for details
DevConfCZ, Feb 2015
Some architecture...
DevConfCZ, Feb 2015
Live Snapshot
● Capture disks and memory at a point in time
● Implemented using qcow2 volume chains
● Usages
– Save the state before a major change
● Can be previewed or reverted
– VM live backup
– Live Storage Migration
DevConfCZ, Feb 2015
The next logical step...● Bug 647386 - Support live deletion of a
snapshot / live-merge– Reported against RHEVM 2.3.0 (Oct. 2010)– 27 customer tickets– http://www.ovirt.org/Features/Live_Merge
● So what's the big deal?
DevConfCZ, Feb 2015
An actual conversation...
DevConfCZ, Feb 2015
An actual conversation...
DevConfCZ, Feb 2015
An actual conversation...
DevConfCZ, Feb 2015
An actual conversation...
DevConfCZ, Feb 2015
Problem 1 – What if a merge fails?
DevConfCZ, Feb 2015
Problem 1 – What if a merge fails?
DevConfCZ, Feb 2015
Solution 1 – Single Disk Snapshots
http://www.ovirt.org/Features/Single_Disk_Snapshot
DevConfCZ, Feb 2015
Problem 2 – long running tasks...● Up to 3.5.0, oVirt has two kinds of verbs
to communicate with VDSM:– Synchronous verbs
● Finish in under 3 minutes● Give result immediately
– Asynchronous ● May take a long time to complete● Return a task to be monitored● Only run on SPM
– Engine commands have up to 3 stages● executeAction() - Synchronous database + VDSM● Poll the task until it completes (or fails) ● endSuccefully() / endWithFailure()
DevConfCZ, Feb 2015
Solution 2 - SEAT● A mechanism was added for Serial Execution of Asyncronous Tasks– http://wiki.ovirt.org/Features/Serial_Executi
on_of_Asynchronous_Tasks– Allows creating chains of actions:
● execute ● poll for a task● move to the next execution...● ... or rollback everything
DevConfCZ, Feb 2015
Solution 2 – Why would I even...● Live Storage Migration
– http://www.ovirt.org/Features/Design/StorageLiveMigration
● Utilizes SEAT for a series of tasks:– [Live Snapshot – not mandatory]– Clone image structure– Start syncing active image– Sync backing chain– Stop sync– Remove (and wipe) source
DevConfCZ, Feb 2015
Problem 3 – Still only SPM tasks● Up to 3.5.0, only SPM can run
asynchronous tasks– This is due to the requirement to persist task
info on the master domain
DevConfCZ, Feb 2015
Solution 3 – HSM “Tasks”● Separate the coordination code from the
polling code– http://www.ovirt.org/Features/Design/Comma
ndCoordinator– Report the progression of the block job on the
pooled VM stats
● Now the HSM that runs the VM can run the merge verb– The basis for rewriting VM migration– The basis for removing the SPM completely
● Come here all about it in DevConfCZ 2016!
DevConfCZ, Feb 2015
A quick shoutout
DevConfCZ, Feb 2015
THANK YOU!
Feedback appreciated: http://devconf.cz/f/79
Stay in touch:[email protected]@mureinikhttps://il.linkedin.com/pub/mureinik
Patches welcome:http://www.ovirt.org