Cloud computing and n-tier apps

[Abhishek Pamecha]

Hi

Given the way clouds totally abstracts out the physical deployment architecture from the applications how does the traditional n-tier deployment architecture fit in a cloud? In other words, how do (will)  enterprise level applications be deployed in a public cloud which can still be tiered separately and managed at the discretion of the application set owner ?

Or does it mean, clouds are more for the analogous mom-pop shops of the internet and "mini loans for storage and computing" but not optimized for applications with affinity to each other because they belong to the same enterprise.


thanks
abhishek

[Jan Klincewicz]

Actually n-tier apps are very well suited to virtualization, in the sense that VMs can easily be "sized" according to tier WRT # of CPUs, RAM etc, while still remaining quite homogeneous.   Also, networking with virtual NICS and switches within a physical host means that network transactions among VMs residing on the same PHYSICAL host do not need to traverse external cable, routers, etc. (and may not even need IP addresses which can assist in security)  Finally, because a good rule of thumb is to balance workloads on a host, the fact that separate VMs in an "n-tier" configuration will likely have different needs for CPU, I/O and memory, there is pretty good likelihood that such a host would already be somewhat in balance.

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Cheers,
Jan

[Tal M. Klein]

Hi Abhishek,

What I'm seeing with a lot of Xen deployments is that people are using
networking to recreate the tiers in the cloud. Even though apps are
deployed on shared hardware, the network is set up such that the vm's
cannot communicate with each other, so basically they are either using
physical or virtual networking separate the apps into subnets that
retain the legacy tiered infrastructure.

-Tal

[Barr, Bill]

Do you mean N-tier apps as defined by hardware vendors or more real-world deployments?

[Abhishek Pamecha]

Jan

Except for the first point you mentioned, wouldnt the same advantages apply to a single tier deployments as well? There would be some reason why the enterprise deployments moved to n-tier in the past? Wouldnt we lost those advantages now ? if we use VMs in the way you suggest, then would this mean that we effectively come back to single-[ physical ] tier applications?

My knowledge is nascent wrt deployment architectures but I would assume a major benefit of muti-tier arch is separate physical network zones for each tier and separate security policies for each of them. Since cloud forces us to relinquish control over these zones/pools/meshes, as data centers are not managed by the enterprise any more,  how do we realize such architectures in a public cloud with sufficient control ?

-abhishek

[Abhishek Pamecha]

Bill

I am more interested in real-world deployments traditionally at enterprise data centers.

-abhishek

[Abhishek Pamecha]

hi Tal

Thanks, thats what I was looking for. Would you have any references for such or examples of such deployments ? What networking components are virtualized ? Does this mean a specific policy is applied manually to a set of hosts [ VMs ]  so that they logically fall in the same tier OR are there separate VMs to simulate networking components too and thus a virtual network is realized using those?

Does anyone currently provide those virtualized networking components for configuring tiers [ basically collecting VMs in a single tier and separating them from other tiers ] in the cloud ?

-abhishek

[Jan Klincewicz]

When I think of n-tier application, I am think of the classic database on the back end, application server in the middle, and web-server interface.  If that is not what you are describing, then I apologize, as I am confused.  If that example DOES match what you are thinking of, then the reason virtualization is a good candidate for such architectures is that typically a single (or more)  physical server(s) is required for each tier. 

While a database is an example of an application that can typically consume most or all of the resources of a physical server, many apps, and all webservers will only use a minuscule portion of a modern server.  Wasting space, electricity, and cooling is reason enough to want to consolidate those workloads onto fewer boxes.  Reducing cables and using fewer physical switch ports is still another.  Certainly, an application and a webserver could both probably co-exist on a single OS on a single physical server, but for whatever reason (consistency, policy, fear of conflicts) many IT folks have chosen to segregate functions by physical server.   As Virtualization simulates this segregation logically, the same results are achieved with less hardware.  The tiers are not lost, but they are no longer isolated by sheet metal nor dependent on fragile Cat5 cable.

[Patrick J Kerpan]

Yes.

Cloud Overlay Networking does this. 

Cisco announced details about "OTV" (overlay transport virtualization) as an overlay capability for data centers and cloud service providers this week.
http://www.datacenterknowledge.com/archives/2010/02/07/cisco-otv-moving-vms-across-data-centers/

CohesiveFT provides overlay networking capabilities for cloud-users (as opposed to cloud providers).

Mark Masterson from CSC tackles the whole concept of enterprise cloud with overlay networking as a big part of his analysis.
http://www.jroller.com/MasterMark/entry/the_enterprise_cloud

Christopher Hoff on VPN-Cubed overlay networking
http://rationalsecurity.typepad.com/blog/2008/11/cohesiveft-vpn-cubed-not-your-daddys-encrypted-tunnel.html

Dmitriy Samovskiy (CohesiveFT engineer) on why one needs overlay networking.
http://somic.org/2009/12/18/cloud-overlay-networks-demystified-holiday-edition/

[Tal M. Klein]

Hi Abhishek,

One of the examples I'm thinking of is a company that has their web
and application tiers virtualized on the same hardware. The web
servers are on one VLAN1 and the app servers are on VLAN2. The VLAN1
traffic is mapped to physical NIC 1 and VLAN 2 is mapped to physical
NIC 2 on each physical host. In other environments I've seen companies
do the same thing but higher up the OSI stack, essentially assigning
each "tier" IP ranges on different subnets and then using a layer 3
device to essentially act as referee.

-Tal