SOAP Routing: The Missing Link

1
SOAP Routing The Missing Link

• Rohit Khare
• 16 May 2002
• OReilly Emerging Technology ConfUC Irvine
  KnowNow, Inc.

2
Our Vision

• The future of software development requires
  integratingnetwork services that are very far
  away and owned by strangers

3
Three Elements of Our Vision

• The abstract unit of software is a network
  service
• Prior levels of abstractions were subroutines,
  libraries, processes, objects,
• In this view, the only way to understand software
  is to watch its message traffic
• Latency is an absolute limit of system
  architecture
• Just as real architects grapple with gravity,
  so with the speed of light
• London will always be 30ms from New York,
  regardless of Moores Law
• Decentralization means crossing agency boundaries
• The essential complication above and beyond
  distributed (parallel) computing is extending a
  system to achieve consensus between several
  separate agencies
• Every computing and communication device is owned
  by someone.

4
How Our Vision is Emerging Today

• The technological shift from a component model to
  a service model of software is already underway
• SOAP and Web Services technologies make it easy
  to write new protocols
• The Internet is inexorably shifting to
  higher-latency, decentralized connectivity
• Ad-hoc, peer-to-peer networking, mainly wireless,
  is being deployed at every scale from one meter
  (handhelds) to billions of meters (space probes)
• Enterprise Application Integration (EAI) is only
  now reaching outside the firewall to business
  partners
• The next revolution in productivity requires
  reengineering processes end-to-end

5
So Whats This Talk About?

• There is a missing link between the near-future
  predicted by todays Web Services hype and
  realizing the true potential of our vision
• It is a new architectural style for software
  integration we call Application-Layer
  Internetworking (ALIN)
• ALIN applies networking concepts to software
  engineering
• The primary way that developers will use ALIN is
  an unheralded implication of SOAP 1.2 Routing
• so this talk is about a new style and a new
  device

6
Talk Overview

• Whats really new about Web Services
• What a SOAP Router is
• What a SOAP Router can do for you
• How an SOAP Router works
• ALIN in theory
• ALIN in practice

7
Web Services are NOT New

• There is nothing new under the sun in distributed
  (or parallel , or grid, ) computing
• These are all efforts to lash many systems
  together to act as one
• SOAP today is a distributed computing technology
• Sprinkling angle-bracket pixie dust over plain
  ol client/server RPC
• Sure, it works across the public Internet, but
  only by treating it as a very slow LAN
• Trade rags already lament the gap at this
  boundary real security, reliability, and
  performance problems reveal the fallacy of
  assuming TCP/IP just works

8
Web Services ARE new

• Decentralization does pose brand-new challenges
• Latency
• Services are no longer mere milliseconds away.
• We need middleware for seconds up to weeks
• Agency
• Services can be owned by other organizations
• We need middleware for translating semantics
• Because SOAP messages are self-contained, they
  can be stored, analyzed, and replayed at will

9
SOAP is Simpler Than You Think

• Starts w/point-to-point, synchronous invocations
• just as Web page servers are accessed today
• Main virtue is that it is not DCOM, IIOP, or RMI
• Encapsulates the messy details of cross-platform,
  cross-language binding using standard marshalling
  formats
• Getting started requires very little
  re-education.
• On the other hand, straight RPC message exchange
  patterns (MEPs) dont inherently reduce the tight
  coupling between client and server semantics.

10
SOAP is Cooler Than You Think

• The vastly underestimated power of SOAP is that
  its model is genuinely asynchronous
• Today, we use it as a form of XML RPC
• Underneath, thats merely a pair 1-way messages
• Furthermore, SOAP Actors are not hosts
• An actor is a much more general concept than a
  fixed service provider machine and port
• One actor may be a proxy for many others
• Ideally, actors represent actual business models

11
What is SOAP Routing?

• Today, the canonical Web Services diagram
  directly connects SOAP endpoints
• There will also be a complementary technology
  that sits in the middle
• Store-and-forward reliable messaging
• Filtering, transformation, analysis of flows
• Intelligent active proxy chaining of actors

12
What Good is SOAP Routing? 1/2

• Internet-scale Middleware
• Just as distributed objects needed
  message-oriented-middleware (MOM)
• decentralized services will need mediators
• Wrappers SOAP brokers to legacy systems
• Monitors SOAP transaction correlation audit
• Queues decouples SOAP provider from requestor
• Pub/Sub decouples SOAP actors entirely
• The difference is coping with firewalls and other
  kinds of agency boundaries

13
What Good is SOAP Routing? 2/2

• Add new ilities without modifying either end.
• Security Router can authenticate and authorize
• Reliability Router can store-and-forward msgs
• Availability Router can redirect to live servers
• Scalability Router can redistribute messages
• Interoperability Router can transform msgs
• Interactivity Router can update msgs in-flight
• Routing lets us reason about a network of
  services -- not just pipelines, but graphs

14
How SOAP Routing Works 1/2

• Consider a simple Bank ATM service
• In the old world, you would have fine-grained
  account objects and setUserName() functions
• As Web Services, you have more flexible
  XML-document services like getStatement()
• A client-side ATM program can easily call it
  directly today by composing a SOAP message and
  POSTing it to the Bank server

15
How SOAP Routing Works 2/2

• First, it provides simple middleware
• Recall how CGI scripts directly invoked scripts.
• Later, Application Servers emerged to
  encapsulate the effort of storing state c
• By passing the message through a SOAP router
• It can enforce the Banks security policy
• It can store a copy of the message for audit logs
• It can redirect requests across a server farm
• This is exactly what Web proxies do today

16
How SOAP Routing Helps 1/2

• Second, it affords flexibility of connections
• What if you wanted to change banks?
• The router can filter the captured message stream
  so that messages from the new bank look like
  the old bank
• What if you wanted to change currencies?
• This is equivalent to routing through another
  actor
• The router can transform messages with plugin
  scripts today, XML schemas tomorrow
• What if you wanted to know if cash is running
  out?
• The router can analyze messages for trends

17
How SOAP Routing Helps 2/2

• Third, it allows 3rd 4th-party extensions
• What if you wanted to check on your bonds, too?
• The router can multicast the balance inquiry to
  the Bank service and a Broker service
• What if you wanted to buy more bonds?
• The router can monitor the joint transaction of a
  money transfer to the broker and the purchase of
  the bonds
• What if you wanted your limit kids access?
• The router can delegate access control rights

18
ALIN in theory 1/3

• ALIN is NOT merely Actor intermediation (piping)
• Actor chains today are like UUCP !path
  addressing its source-routing only
• Its the ability to infer semantic chains,
  decouple political control, etc.
• SOAP Routers directly address the twin novel
  challenges of decentralized service integration
• Latency
• by decomposing every communication into a
  one-way, asynchronous message, routers force us
  to confront extreme latency, rather than hiding
  it
• Agency
• by introducing a trusted 3rd-party between the
  original endpoints, routers allow us to represent
  the interests of many other 4th-party agencies

19
ALIN in theory 2/3

• The Internet itself is a result of addressing
  high latency and diverse agency at Layer 3
• IP Routers store-and-forward packets across
  autonomous systems, each containing many LANs
• IP-format packets are a generic interchange for
  LANs
• Consequently, Internet-scale services must
• Scale Across Time Interfaces must be stable for
  decades
• Scale Across Space Protocols must handle gt100ms
  delays
• Scale Across Organizations Namespaces must
  peer
• This is merely an application-layer router for
  TPs

20
ALIN in theory 3/3

• This architectural style builds on REST C2
• Beyond merely transferring representation, now we
  can mediate them
• Can connect any graph, not just a strict lattice
• It generalizes other MOM styles
• Queues, sync/async, 1-1, N-N, transactional
• Pub/Sub, address-based and content-based
• The most contentious aspect of ALIN for MOM folks
  is best-effort it is still difficult to sell
  TCP over IP
• If your bottom turtle is already transactional,
  it rules out scalability and perf
• The very definition of agency boundary is that
  transactions cant span them!

21
ALIN in practice

• Lots of ink is being spilled on missing
  infrastructure for Web Services
• Major software platform vendors are only
  beginning to market RPC-style Web Services
• Existing middleware products are having
  difficulty outside the firewall
• JMS, for example, is single-vendor,
  single-language
• High-performance EAI tools often assume multicast
  IP
• Early Internet-scale messaging startups include
  KnowNow, Bang, Kenamea, SonicXQ, Grand Central,
  and others
• Microsoft has outlined its WS-Routing proposal
• IBM has Business Rule Beans and MQ Event Broker
  in WS5.0

22
Distributed vs. Decentralized

• We already have lots of techniques for
  decomposing systems to run on many distributed
  processors acting as one
• The genuinely novel potential of Web Services is
  decentralization
• Marketplaces, rather than central brokers
• Routing is a new technique for integrating
  services provided by 3rd and 4th parties

23
A Parting Thought

• The dirty little secret is that the 7-Layer ISO
  Network model is insufficient to model
  decentralized computing.
• Its really all about integration at Layer 8 9

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