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This is an early draft

Bug Reference

None

Branch

Work in progress patches are here:

https://github.com/djs55/cloudstack/tree/virsh-capabilities

Introduction

Some people prefer to manage their hypervisors entirely via the libvirt control plane. At the moment these people are forced to choose the KVM hypervisor, even though libvirt also supports the Xen hypervisor. This design extends CloudStack to support management of hosts running Xen via libvirt as well as KVM.

Principles

  1. Maximise code shared between KVM and Xen. Corollary: minimise the number of Xen-specific workarounds
    1. We want people to be able to add features to the libvirt plugin without having to write unnecessary special-cases for Xen or KVM.
    2. If a libvirt hypervisor driver lacks a useful feature, we should implement it.
    3. Share the same system VM template as KVM

References

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Document History

Glossary

Feature Specifications

Summary: This design extends the existing KVM/libvirt plugin to be able to manage Xen/libvirt hosts.

Limitations

  • L1: It will not be possible to support clusters of mixed KVM/Xen hosts. This is because it is not possible to live migrate VMs between different hypervisors.

Proposed changes


  • C1: The HypervisorType enum will be extended to include "XEN" (alongside "KVM" and "XENSERVER")
  • C2: Create a "XenLibvirtDiscoverer" as a subclass of LibvirtServerDiscoverer (alongside the KVM and LXC versions).
  • C3: Generalise the cloudutils python function "isKVMEnabled" to "isHypervisorEnabled"
  • C3.1 Detect the Xen hypervisor by reading /sys/hypervisor/type
  • C3.2 Detect the KVM hypervisor by "lsmod | grep kvm"
  • C4. Register a system VM template for the "XEN" hypervisor
  • C4.1 Use the same template image as KVM (including keeping it in .qcow2 format)
  • C5. Use the "xen" PV driver family if using "XEN"; and use "virtio" drivers if using "KVM"
  • C6. Under Xen, by default boot the system VM in PV mode
  • C6.1 Add a config setting to enable system VMs to boot in HVM mode
  • C7 In cloud-early-config under Xen, first check the host private "channel" and fall back to the command-line parsing

Dependencies on other projects

This work will depend on changes and improvements in other open-source projects:

  • D1 Xen's libxl needs to support  


  • put a summary or a brief description of the feature in question 
  • list what is deliberately not supported or what the feature will not offer - to clear any prospective ambiguities
  • list all open items or unresolved issues the developer is unable to decide about without further discussion
  • quality risks (test guidelines)
    • functional
    • non functional: performance, scalability, stability, overload scenarios, etc
    • corner cases and boundary conditions
    • negative usage scenarios
  • specify supportability characteristics:
    • what new logging (or at least the important one) is introduced
    • how to debug and troubleshoot
    • what are the audit events 
    • list JMX interfaces
    • graceful failure and recovery scenarios
    • possible fallback or work around route if feature does not work as expected, if those workarounds do exist ofcourse.
    • if feature depends other run-time environment related requirements, provide sanity check list for support people to run
  • explain configuration characteristics:
    • configuration parameters or files introduced/changed
    • branding parameters or files introduced/changed
    • highlight parameters for performance tweaking
    • highlight how installation/upgrade scenarios change
  • deployment requirements (fresh install vs. upgrade) if any
  • system requirements: memory, CPU, desk space, etc
  • interoperability and compatibility requirements:
    • OS
    • xenserver, hypervisors
    • storage, networks, other
  • list localization and internationalization specifications 
  • explain the impact and possible upgrade/migration solution introduced by the feature 
  • explain performance & scalability implications when feature is used from small scale to large scale
  • explain security specifications
    • list your evaluation of possible security attacks against the feature and the answers in your design* *
  • explain marketing specifications
  • explain levels or types of users communities of this feature (e.g. admin, user, etc)

Use cases

put the relevant use case/stories to explain how the feature is going to be used/work

Architecture and Design description

  • discussion of alternatives amongst design ideas, their resources/time tradeoffs and limitations. Explain why a certain design idea is chosen over others
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  • talk about main algorithms used
  • explain what components are being changed and what the dependent components are
  • regarding database: talk about tables being added/modified
  • performance implications: what are the improvements or risks introduced to capacity, response time, resources usage and other relevant KPIs
  • preferably show class diagrams, sequence diagrams and state diagrams
  • if possible, publish signatures of all methods classes and interfaces implement, and the explain the object information of different classes

Web Services APIs

list changes to existing web services APIs and new APIs introduced with signatures and throughout documentation

UI flow

  • either demonstrate it visually here or link to relevant mockups

IP Clearance

  • what dependencies will you be adding to the project?
  • are you expecting to include any code developed outside the Apache CloudStack project?

Appendix

Appendix A:

Appendix B:

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