Techniques for Composing REST services

Transcription

1 Techniques for Composing REST services Cesare Pautasso Faculty of Informatics University of Lugano, Switzerland

2 Abstract Novel trends in Web services technology challenge the assumptions made by current standards for process-based service composition. For example, most existing RESTful Web service APIs (which do not rely on the Web Service Description Language), cannot natively be composed using the WS-BPEL language. In this talk we introduce the problem of composing RESTful services and compare it to Web 2.0 service mashups. We cover several real-world examples demonstrating how existing composition languages can be evolved to cope with REST. We conclude by showing that the uniform interface and hyperlinking capabilities of RESTful services provides an excellent abstraction for exposing in a controlled way the state of business process as a resource Cesare Pautasso 2

3 About Cesare Pautasso Assistant Professor at the Faculty of Informatics, University of Lugano, Switzerland (since Sept 2007) Research Projects: SOSOA Self- Organizing Service Oriented Architectures CLAVOS Continuous Lifelong Analysis and Verification of Open Services BPEL for REST Researcher at IBM Zurich Research Lab (2007) Post- Doc at ETH Zürich Software: JOpera: Process Support for more than Web services Ph.D. at ETH Zürich, Switzerland (2004) Representations: (Web) (Twitter Feed) Cesare Pautasso 3

4 Why Composition? Composition is the key SOA principle with the goal of enabling service reuse Cesare Pautasso 4

5 REST and Reuse Uniform Interface (Reuse Contract) Status Codes (Reuse Metadata) Representations (Reuse Media Types) Middleware (Reuse caching, security, load balancing, proxies components) Cesare Pautasso 5

6 REST in one slide Web Services expose their data and functionality trough PUT resources identified by URI R Uniform Interface Principle: Clients interact with resources through a fix set of verbs. Example HTTP: (read), (create), PUT (update), Multiple representations for the same resource Hyperlinks model resource relationships and valid state transitions for dynamic protocol description and discovery Cesare Pautasso 6

7 REST and Reuse Uniform Interface (Reuse Contract) Status Codes (Reuse Metadata) Representations (Reuse Media Types) Middleware (Reuse caching, security, load balancing, proxies components) Yes, but what about reusing entire RESTful services? Cesare Pautasso 7

8 RESTful Composition Techniques 1. Defining RESTful service composition 2. Example: DoodleMap 3. What about mashups? 4. BPM and REST Cesare Pautasso 8

9 REST Architectural Elements Client/Server Layered Stateless Communication Cache Proxy User Agent Origin Server Gateway Connector (HTTP) Cache Cesare Pautasso 9

10 Basic Setup HTTP User Agent Origin Server Adding Caching HTTP HTTP Caching User Agent Origin Server HTTP User Agent Caching Origin Server Caching User Agent Caching Origin Server Cesare Pautasso 10

11 Proxy or Gateway? Intermediaries forward (and may translate) requests and responses HTTP HTTP Client Proxy Origin Server A proxy is chosen by the Client (for caching, or access control) HTTP HTTP Client Gateway Origin Server The use of a gateway (or reverse proxy) is imposed by the server Cesare Pautasso 11

12 REST Middleware for Scalability Cache Clients Proxy/Gateway Origin Server One example of REST middleware is to help with the scalability of a server, which may need to service a very large number of clients Cesare Pautasso 12

13 REST Middleware for Composition Clients Proxy/Gateway Origin Server Composition shifts the attention to the client which should consume and aggregate from many servers Cesare Pautasso 13

14 REST Middleware for Composition Client Composite RESTful service Origin Servers The proxy intermediate element which aggregates the resources provided by multiple servers plays the role of the composition controller of a composite RESTful service Cesare Pautasso 14

15 Composite Resources PUT C PUT PUT R S Cesare Pautasso 15

16 Composite Resources The composite resource only aggregates the state of its component resources C R S State R State S Cesare Pautasso 16

17 Composite Resources The composite resource augments (or caches) the state of its component resources C State C R S State R State S Cesare Pautasso 17

18 Enter HATEOAS Web Services expose their data and functionality trough PUT resources identified by URI R Uniform Interface Principle: Clients interact with resources through a fix set of verbs. Example HTTP: (read), (create), PUT (update), Multiple representations for the same resource Hyperlinks model resource relationships and valid state transitions for dynamic protocol description and discovery Cesare Pautasso 18

19 Composite Representations Composite Representation C Link R PUT R PUT S Link S Cesare Pautasso 19

20 Composite Representation Pattern Composite Representation Origin Server Client Origin Servers A composite representation is interpreted by the client that follows its hyperlinks and aggregates the state of the referenced component resources Cesare Pautasso 20

21 Bringing it all together Composite Representation Composite RESTful service Origin Servers Client Origin Servers A composite representation can be produced by a composite service too Cesare Pautasso 21

22 Doodle Map Example Composite Representation Composite RESTful service Origin Servers Client Origin Servers Vote on a meeting place based on its geographic location Cesare Pautasso 22

23 1. Composite Resource PUT C PUT PUT R S Cesare Pautasso 23

24 1. Composite Resource C PUT R S Cesare Pautasso 24

25 2. Composite Representation DM G Link G Link C C PUT Link D R S Cesare Pautasso 25

26 Demo Cesare Pautasso 26

27 Was it just a Mashup? Mashup REST Composition (It depends on the definition of Mashup) Cesare Pautasso 27

28 Moving state around Read-only vs. Read/Write PUT C PUT PUT R S Cesare Pautasso 28

29 Simply aggregating data (feeds) Read-only vs. Read/write C R S Cesare Pautasso 29

30 Is your composition reusable? UI vs. API Composition Client Composite Representation UI Origin Servers Composite RESTful service API Origin Servers Reusable services vs. Reusable Widgets Cesare Pautasso 30

31 Single-Origin Sandbox Can you always do this from a web browser? Composite Representation Composite RESTful service Origin Servers Client Origin Servers Cesare Pautasso 31

32 Single-Origin Sandbox Security Policies on the client may not always allow it to aggregate data from multiple different sources Composite Representation Composite RESTful service N Origin Servers Client 1 Origin Server Cesare Pautasso 32

33 Complementary Read-Only Read/Write UI Mashup REST API Composition Situational Sandboxed Reusable Service Cesare Pautasso 33

34 RESTful Composition Techniques 1. Defining RESTful service composition 2. Example: DoodleMap 3. What about mashups? 4. BPM and REST Cesare Pautasso 34

35 Web Service Composition Today The WS-BPEL process model is layered on top of the service model defined by WSDL 1.1. [ ] Both the process and its partners are exposed as WSDL services WS-BPEL 2.0 WSDL 1.1 [BPEL 2.0 Standard, Section 3] Cesare Pautasso 35

36 RESTful Web Services APIs WSDL 1.1 do not use WSDL Cesare Pautasso 36

37 BPEL/WSDL 2.0 WSDL 2.0 HTTP Binding can wrap RESTful Web Services (WS-BPEL 2.0 does not support WSDL 2.0) BPEL... <Invoke Op_1> <Invoke Op_2> WSDL 2.0 Operations Op_1 Op_2 Op_3 Op_4 PUT R... <Invoke Op_3> <Invoke Op_4>... HTTP Binding Op URI Method Op_1 R PUT Op_2 R Op_3 R Op_4 R Cesare Pautasso 37

38 BPM Workflow Languages RESTful Web Service Composition Cesare Pautasso 38

39 Solutions 1. Abstract Workflow Service invocation technology does not matter 2. Concrete Workflow Expose service invocation technologies as explicit constructs in the workflow language 3. RESTful Workflow Workflow as one kind of resource exposed by a RESTful service BPM Workflow Languages RESTful Web Service Composition BPM RESTful Workflow Web Service LanguagesComposition BPM RESTful Workflow Web Service Languages Composition Cesare Pautasso 39

40 BPEL/WSDL 2.0 WSDL 2.0 HTTP Binding can wrap RESTful Web Services (WS-BPEL 2.0 does not support WSDL 2.0) BPEL... <Invoke Op_1> <Invoke Op_2> WSDL 2.0 Operations Op_1 Op_2 Op_3 Op_4 PUT R... <Invoke Op_3> <Invoke Op_4>... HTTP Binding Op URI Method Op_1 R PUT Op_2 R Op_3 R Op_4 R Cesare Pautasso 40

41 BPEL for REST Make REST interaction primitives first-class language constructs BPEL for REST... <Put R> <Get R>... <Post R> <Delete R>... PUT R Cesare Pautasso 41

42 BPEL for REST Dynamically publish resources from BPEL processes and handle client requests PUT P BPEL for REST PUT <Resource P> <onget> <Put R> <Get S> </onget> <ondelete> <Post R> <Delete S> </ondelete> </Resource> Cesare Pautasso 42 R PUT S

43 RESTful Workflows PUT P R Use the resource interface abstraction to publish the state of the workflow Cesare Pautasso 43

44 DoodleMap as RESTful workflow Cesare Pautasso 44

45 Conclusion Applying the SOA composition principle to REST gives interesting results Thanks to hyperlinks, REST brings a new (more dynamic and loosely coupled) twist to SOA composition Composing RESTful services helps to build mashups, but is different A RESTful API is the perfect abstraction for publishing the state of a workflow Cesare Pautasso 45

46 References R. Fielding, Architectural Styles and the Design of Networkbased Software Architectures, PhD Thesis, University of California, Irvine, 2000 C. Pautasso, O. Zimmermann, F. Leymann, RESTful Web Services vs. Big Web Services: Making the Right Architectural Decision, Proc. of the 17th International World Wide Web Conference (WWW2008), Bejing, China, April 2008 C. Pautasso, BPEL for REST, Proc. of the 7 th International Conference on Business Process Management (BPM 2008), Milano, Italy, September 2008 C. Pautasso, Composing RESTful Services with JOpera, In: Proc. of the International Conference on Software Composition (SC2009), July 2009, Zurich, Switzerland. 46

47 Raj Balasubramanian, Benjamin Carlyle, Thomas Erl, Cesare Pautasso, SOA with REST, Prentice Hall, to appear in Cesare Pautasso 47