Engine Core - oVirt workshop November 2011

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Backend Bean

  • anything user does is a command queries for information statistics, etc

Entry Point

  • RunMultipleActions runs asynchronously
  • RunPublicQuery runs w/o Authentication

VDS Broker

  • SPM = storage commands
  • Moves SPM owner at failover

Transaction Management

  • RequresNew = suspend current transaction, complete new transaction, resume old transaction
  • Manual transaction management is necessary because of different contexts (user requested vm start vs. starting a vm as part of a large task - e.g. failover)
  • Transactions are about keeping the database consistent / not about tracking individual actions/processes

Road Map (of non-obvious features)

  • Have all consumers consolidate on the REST API
  • Establish a BUS for communication on the backend
  • Networking: Integrate on Qbg/h manager
  • Task Management: Today, engine can’t tell what is being executed by the backend
  • Command Prioritization: e.g. give HA VM commands priority over others
  • Abstract out policies in backend into existing policy engine
  • multiple DB vendors - e.g. MemoryHDB
  • HA: having an active/active deployment
  • Scale out - have multiple backends monitoring each host

Questions & Answers

  • Q: How do oVirt nodes deal with a crashed/rebooting backend?
    • A: VMs are not affected; they keep running. But a double failure can occur causing an HA VM to not get restarted. Possibly have oVirt engine send policy to each host so they know who their backups are.
  • Q: If Host crashes?
    • A: Backend can fence the host and restart VMs elsewhere.
  • Q: How do we determine if a host is down?
    • A: Engine polls VDSM every 2s; if host is unresponsive it goes into a trying-to-connect; after 60s host is considered non-responsive
  • Q: How often do we pull stats from the guest?
    • A: We don’t - we pull it from the host which aggregates data, and every 2s. Also get updates from the guest agent (don’t remember the rate of updates for the guest)

Category: Workshop November 2011