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Concrete Services

Concrete Services. Making SOA real. Service Orientation. What is Service-Orientation? …. Service Orientation. What is Service Orientation? A buzzword Hype Empty promises A chance for consultants to make more money with vague and undefined technology. Service Orientation.

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Concrete Services

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  1. Concrete Services Making SOA real

  2. Service Orientation • What is Service-Orientation? • …

  3. Service Orientation • What is Service Orientation? • A buzzword • Hype • Empty promises • A chance for consultants to make more money with vague and undefined technology

  4. Service Orientation • Services are about creating loosely-coupled systems for maximum flexibility and evolution • No “objects” • No RPC • No assumption of platform • No code-generated remote proxy dependencies • No implicit assumption of network availability • Services are real, if you cut through the bull

  5. Pragmatic Services • Problem: Performance • Too many remote method calls creates latency • Remote events • Remote collections (“n+1 query problem”) • Object-orientation works great in-memory, but … • Solution: Avoid round trips; batch calls instead • No remote events • No remote methods • No remote properties • In short, no remote objects • Remote objects create too many remote calls • Look to collate multiple calls into one (e.g., DAOs)

  6. Pragmatic Services • Problem: Evolution • Interface-based remoting creates tightly coupled proxies • Implies that if the interface changes, so must the proxies • But not all clients want to recompile just to support your changes • Works great when both clients and servers are controlled by one entity, but not across entities • Solution: Avoid interfaces • Prefer to exchange loosely-bound data • Untyped collections (Lists, Sets, Maps, etc) • Database result types (DataSets, RowSets) • In short, “messages”: JMS, MQSeries, TIBCO, MSMQ • But this requires greater documentation discipline

  7. Pragmatic Services • Problem: Exponential message defintions • Developers start creating a new message type for every possible operation/message • NewUserRequestMessage, NewUserResponseMessage, … • Creates confusion and duplication of effort • Solution: Create “action” vocabulary • HTTP uses 7 “verbs” to indicate message intent • Create a similar scheme for your message types • So only one “User” type is needed, plus “Create”, “Update”, “Retrieve” and “Delete” actions for each • Allows for easy extension and intermediary manipulation

  8. Pragmatic Services • Problem: Online/offline support • Network infrastructure is not reliable • All ORPC toolkits assume 24x7 network support • So if the network disappears, client proxies are toast • Clients aren’t always online, anyway • Email clients, for example, work just as well off- as online • Networks are many places, but not everywhere • Solution: Use reliable messaging infrastructure • Let messaging plumbing hold the message for delivery • Retries, transactional delivery, intermediaries • Can use other tools, too—filesystem, database, …

  9. Pragmatic Services • Problem: Interoperability • The world is not flat, nor is it homogeneous • J2EE, .NET not going away, Ruby/Rails making a surge • It’s a fact: You’ll have to talk to the Other Guys • But objects don’t serialize well across platforms • Binary formats are close, but not identical • Typesystems don’t match • Objects don’t serialize well to XML, either • Witness the object/hierarchical impedance mismatch • Solution: Don’t send objects, send XML • Messages are two parts: headers + payload • In other words, SOAP 1.2 messages • XML Schema is helpful… but not required!

  10. Pragmatic Services • Problem: Transport • Everybody’s got their favorite transport: HTTP, TCP, SMTP/POP3, MSMQ, JMS, … • Standardizing on one doesn’t fit all situations or needs • Asynchronicity, fire-and-forget, pub-sub, broadcast, security • No one transport offers all options • Solution: Transport agnosticity • Don’t rely on just one transport • Build messages that can flow across any transport • Implies addressing and routing information are in message • WS-Addressing

  11. Pragmatic Services • Problem: Scalability • When object systems try to scale, difficulties arise • Object identity creates contention • Simple caching fails on 2+ machines • Cache update propagation is difficult to achieve with objects • Object-based scaling systems (EJB, MTS/COM+) are complex • Solution: Assume for scalability • Don’t hold request context across requests • Make messages context-complete • Don’t cache writeable data in memory • Only read-only or read-mostly data is safe to cache • Be location-neutral • You know it’s remote, you just don’t care where

  12. Pragmatic Services • Problem: Legacy code • How does legacy COM/COM+/Java/CORBA/C++/C# fit in? • Much less CICS, Tuxedo, … • Orchestration implies big buy in (BizTalk, BPEL) • Solution: Legacy code is just another transport • Place a service adapter in front of the legacy code • Messages in, messages out

  13. Pragmatic Services • Problem: Security • When adopting transport agnosticity, can’t rely on the transport (HTTP/S) for confidentiality • Many transports aren’t secure by default • Mustn’t assume the firewall provides perfect security • Solution: CIA at the message level • Provide Confidentiality/Integrity/Authenticity at the message level, not at the transport level • XML Encryption, XML Digital Signature, and other specifications provide confidentiality and integrity to XML messages • WS-Security discusses authentication forms • Java Crypto API provides same for Java messages • JAAS provides authentication & authorization for Java

  14. Pragmatic Services • Problem: Reliable delivery • Some messages cannot be lost (legal, medical, financial) • Not all transports provide best-effort delivery • No transport can provide absolute guaranteed delivery • Message loss not highly visible in small LAN environments • Despite this, messages must still get through • Solution: Reliable messaging • Elevate Quality-of-Service considerations into the message itself • At-Most-Once, At-Least-Once, Once-And-Only-Once • Transacted delivery • Transport-agnostic, though transports may help guarantees

  15. Pragmatic Services • Problem: Firewalls and perimeter security • Integration means crossing trust boundaries • Firewalls are often not under development control • VPN doesn’t solve the problem • often grants “too much” access • infrastructure support grows exponentially with new partners • Recent legislation only heightens security paranoia • Solution: Use transport agnosticity to respect it • Put an intermediary in solely to bridge the firewall • May require moving across a different transport (HTTP) • May do application-level firewalling of messages, as well

  16. Pragmatic Services • Problem: Multiple identity domains • Credentials aren’t scoped to the system • Users won’t span all parts of the system • Authorization often varies per system/user tuple • Some users won’t even be users, but silicon-based lifeforms • IT uses a variety of credential/authorization systems • Kerberos, Passport, LDAP, home-grown, … • Solution: Identity and authorization federation • WS-Trust creates a “web of trust” and brokered auth • Messages can carry multiple credentials if necessary

  17. Pragmatic Services • Problem: How do I get started? • Solution: Depends • All: SOAP 1.2, WS-Addressing, XML Schema • These are simple enough that you can hand-roll your system • WS-Transfer, WS-Enumeration aren’t far from REST • Then consider WSDL 2.0, WS-RM/WS-Reliability, WS-Eventing, WS-Notification-and-friends, WS-Security-and-friends • Java: JAX-WS, JAXB, XMLBeans, JMS/EJB MDBs, … • Look for tools that give you direct access to the SOAP message when you want it but only when you want it • Look for tools that aren’t tied to a particular transport • Don’t use tools that generate WSDL and proxies for you (at first) • Don’t treat XML services as a “black box”; it’s grey, at least

  18. Conclusion • Services do hold promise for integration • … but it’s not going to be the easy “flip-of-the-switch” story that your vendors will try to sell you on • Services seek to minimize coupling across units • … but remember that some coupling is necessary; the trick is to choose when and where • Services can be deployed incrementally • … starting with your object-based systems and slowly evolving them into message-based components

  19. Credentials • Who is this guy? • Independent consultant (Contact ted@tedneward.com) • Speaker • No Fluff Just Stuff, TechEd, JavaOne, VSLive!, and others • Java Community Process EG member (JSR 175, 277, …) • Author • Pragmatic XML Services (Pragmatic Press, forthcoming) • Effective Enterprise Java (Addison-Wesley, 2004) • Server-Based Java Programming (Manning, 2000) • C# in a Nutshell (with Drayton, Albahari; OReilly, 2001) • SSCLI Essentials (with Stutz, Shilling; OReilly, 2003) • Papers at http://www.neward.net/ted/Papers • Weblog at http://blogs.tedneward.com

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