On the many limitations of (network) virtual appliances

Posted by virtualization.info Staff   |   Monday, February 1st, 2010   |  

At virtualization.info there’s a special skepticism about virtual appliances in their current form.
No less than three years ago we wrote about the shortcomings and hidden risks of this virtual machine incarnation. 
A modular data center may certainly be in the future of IT,  but in its implementation, a virtual appliance is not the best way to go there. The lack of enthusiasm from customers, which someone highlighted, is a confirmation.
The VMware effort to enhance the virtual appliance concept with metadata to define security policies and performance SLAs, something the company calls vApp since 2008, is a step in the right direction.

But while waiting for the first wave of vApps and its subsequent generations, there’s still much that can be said on this topic.
Christofer Hoff, Director of Cloud and Virtualization Solutions at Cisco, published an interesting article focusing on the current limitations of network virtual appliances. It’s definitively worth a mention here:

  1. Most of the virtual network appliances, especially those “ported” from the versions that usually run on dedicated physical hardware (COTS or proprietary) do not provide feature, performance, scale or high-availability parity; most are hobbled or require per-platform customization or re-engineering in order to function.
  2. The resilience and high availability options from today’s off-the-shelf virtual connectivity does not pair well with the mobility and dynamism of de-coupled virtual machines; VMs are ultimately temporal and networks don’t like topological instability due to key components moving or disappearing
  3. The performance and scale of virtual appliances still suffer when competing for I/O and resources on the same physical hosts as the guests they attempt to protect
  4. Virtual connectivity is a generally a function of the VMM (or a loadable module/domain therein.) The architecture of the VMM has dramatic impact upon the architecture of the software designed to provide the connectivity and vice versa.
  5. Security solutions are incredibly topology sensitive.  Given the scenario in #1 when a VM moves or is distributed across the pooled infrastructure, unless the security capabilities are already present on the physical host or the connectivity and security layers share a control plane (or at least can exchange telemetry,) things will simply break
  6. Many virtualization (and especially cloud) platforms do not support protocols or topologies that many connectivity and security virtual appliances require to function (such as multicast for load balancing)
  7. It’s very difficult to mimic the in-line path requirements in virtual networking environments that would otherwise force traffic passing through the connectivity layers (layers 2 through 7) up through various policy-driven security layers (virtual appliances)
  8. There is no common methodology to express what security requirements the connectivity fabrics should ensure are available prior to allowing a VM to spool up let alone move
  9. Virtualization vendors who provide solutions for the enterprise have rich networking capabilities natively as well as with third party connectivity partners, including VM and VMM introspection capabilities. As I wrote about here, mass-market Cloud providers such as Amazon Web Services or Rackspace Cloud have severely crippled networking.
  10. Virtualization and cloud vendors generally force many security vs. performance tradeoffs when implementing introspection capabilities in their platforms: third party code running in the kernel, scheduler prioritization issues, I/O limitations, etc.
  11. Much of the basic networking capabilities are being pushed lower into silicon (into the CPUs themselves) which makes virtual appliances even further removed from the guts that enable them
  12. Physical appliances (in the enterprise) exist en-mass.  Many of them provide highly scalable solutions to the specific functions that Alan refers to.  The need exists, given the limitations I describe above, to provide for integration/interaction between them, the VMM and any virtual appliances in order to offload certain functions as well as provide coverage between the physical and the logical.

He concludes with a prediction:

What does this mean?  It means that ultimately to ensure their own survival, virtualization and cloud providers will depend less upon virtual appliances and add more of the basic connectivity AND security capabilities into the VMMs themselves as its the only way to guarantee performance, scalability, resilience and satisfy the security requirements of customers.



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