Distributed architectures: reverse assumptions, still relevant

On a call today, discussion turned to the open-ness – or not! – of today’s infrastructure architectures for “Living on the Web”, as Doug Neal of CSC’s Leading Edge Forum calls it. The comment was made that much of even today’s Microsoft-based infrastructure still embodies assumptions from the days of closed-network architectures.

What did we mean? Living on the Web – for major corporates such as BP and Aviva, who’ve been doing it for some years now – means accepting that the corporate perimeter is not the safe haven often assumed. Nor is it, in today’s business world, practical for business. Companies don’t do everything within the firewall these days. They partner, they outsource, they collaborate. The firewall, and the quasi-security mindset that goes with it, don’t facilitate this way of doing business. They get in the way. There are good reasons why the mindset is there, but they just make it harder to challenge!

BP is well recognised now for adopting the open Internet as its base infrastructure and for treating its user community as IT adults who can often make their own decisions – with support where home-based experience doesn’t translate to corporate needs. Resources that need to be protected are certainly protected, but much closer to source. Access through the firewall isn’t any longer an open sesame to vast swathes of corporate resources. As someone on the call commented, Port 80 is the hacker’s internet these days. And this approach has been audited to show it is more secure, not less.

But – to return to the point – many infrastructure professionals still work from the implicit, probably unrecognised and certainly unquestioned assumptions that it’s best to do it the same way as since the local area network was invented. And I called to mind some work done by a UK project called ANSA (Advanced Networked Systems Architectures) between 1985 and 1998. ANSA was one of the first projects to seriously examine what happened when systems no longer were located on a single computer, but were cooperative systems constructed from components running potentially anywhere worldwide. Internet-based collaborative systems are that, to the nth degree!

ANSA offered a set of assumptions which systems engineers made then, which have to be turned on their head in a distributed environment. We still need to be reminded of some of them:

  • local→remote: more failure modes are possible for remote interactions than for local ones
  • direct→ indirect binding: configuration becomes a dynamic process, requiring support for linkage at execution time
  • sequential→ concurrent execution: true concurrency requires mechanisms to provide sequentiality
  • synchronous→ asynchronous interaction: communication delays require support for asynchronous interactions and pipelining
  • homogeneous→ heterogeneous environment: requires common data representation for interactions between remote systems
  • single instance→ replicated group: replication can provide availability and/or dependability
  • fixed location→ migration: locations of remote interfaces may not be permanent
  • unified name space→ federated name spaces: need for naming constructs which mirror administrative boundaries across different remote systems
  • shared memory→ disjoint memory: shared memory mechanisms cannot operate successfully on a large scale and where remote operations are involved.We’ve got used to working with some of these. But, in the commercial world, many enterprises still want to retain control. In terms of these reverse assumptions, it means not coming to terms with the ones related to federation – name spaces in particular, which includes authentication through federated directories; and heterogeneity, so that not everything in the system accords with the decisions that “we” make about our own architecture. There’s still a way to go!


    ANSA: An Engineer’s Introduction to the Architecture ANSA, 1989, part of the Official Record of the ANSA Project at ansa.co.uk

    Web 2.0: The New Frontier for Employee Responsibility and Innovation CSC Leading Edge Forum, 2007

    You can see how far the theme goes back in BP by reviewing this BP presentation by John Leggate: Exploiting digital technology … (CERA Conference, Houston, 13 Feb 2001)

    Or just Google for “Living on the Web”!

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