Web Services Robert Neumann

119 Cloud Computing

Lecture Lab

08.10.2012 Overview ---

15.10.2012 Cloud Computing & Pricing Introduction

22.10.2012 Cloud Frontend Technologies Hello Cloud

29.10.2012 Web Services Partial SSL

05.11.2012 Cloud Data Management SOAP

12.11.2012 Cloud Storage Technologies Non-relational Storage

19.11.2012 Cloud Scaling & Performance Blob Storage

26.11.2012 Invited Speaker “Kai Jäger” (Microsoft): HTML5 Distributed Cache

03.12.2012 Invited Speaker “Markus Winkler” (IBM): Java EE […]

10.12.2012 Virtualization Hypervisors

17.12.2012 Cloud Scheduling

Auto-Scaling

07.01.2012 Column Stores HBase

14.01.2012 MapReduce Hadoop

21.01.2012 Wrap-up ---

120 Cloud Computing

Service Calling Made Easy

credits

121 Cloud Computing

Web Service Overview

Protocol!

Architecture!

Complements or Competitors?

122 Cloud Computing

SOAP Services – “Big Web Services”

Core Technologies

1. SOAP (Simple Object Access Protocol), 1998

1. Dave Winer

2. Don Box (Microsoft)

3. Bob Atkinson (Microsoft)

4. Mohsen Al-Ghosein (Microsoft)

2. WSDL (Web Service Description Language), 2000

1. Microsoft

2. IBM

3. Ariba

(NASSL (IBM) + SDL (Microsoft) WSDL)

Describes

structure of

Web Service

and its methods

Describes message

exchange between

service provider and

consumer

123 Cloud Computing

Big Web Services

src: wikipedia.org

124 Cloud Computing

SOAP Building Blocks

<?xml version="1.0"?> <soap:Envelope xmlns:soap="http://www.w3.org/2001/12/soap-envelope" soap:encodingStyle="http://www.w3.org/2001/12/soap-encoding"> <soap:Header> ... </soap:Header> <soap:Body> ... <soap:Fault> ... </soap:Fault> </soap:Body> </soap:Envelope>

Application-specific information (e.g., Payment, Authorization)

Call and response information

Fault information

125 Cloud Computing

SOAP Sample

126 Cloud Computing

WSDL Building Blocks

- Service

- Functionality exposed via web protocol

- Port/Endpoint

- Address to the service (e.g., HTTP)

- Binding

- Specifies interface (RPC/Document)

- PortType/Interface

- Operations that can be performed and their messages

- Operation

- Web methods that can be called

- Message

- Types

- XML description of data types

127 Cloud Computing

WSDL Sample

Types for in/out

parameters

WS Method

with in/out

parameters

128 Cloud Computing

SOAP Services - Summary (Chappell, 2009)

- SOAP typically uses XML for information representation

- Pro

- There is one common format

- Cons

- XML isn‘t especially efficient

- XML isn‘t a good fit for some languages

- There is some competition between both

- Yet both have value

- Challenge is to determine when to use what

129 Cloud Computing

SOAP Services - Issues (Chappell, 2009)

- Cross-vendor interop for SOAP and WS technologies isn‘t perfect

- Contract-first design can help

130 Cloud Computing

Representational State Transfer (REST)

Application can be:

1. At rest

2. In transition between application states

REST design goal:

- Maximize use of pre-existing interfaces and capabilities

- Leverage existing infrastructure (e.g. HTTP Caching)

REST vocabulary:

- GET, POST, PUT, DELETE

SOAP Services, in contrast, define their own vocabulary overlaying POST* *(usually)

131 Cloud Computing

REST Constraints

1. Client-server

Clients and servers are separated via uniform interface

2. Stateless

Server does not maintain client context

3. Cacheable

Resources must define themselves as cacheable or not

4. Layered system

System layers are invisible to client

5. Code on demand

Clients can request executable code (Java Script, Applet)

6. Uniform interface

Simplifies and decouples architecture

132 Cloud Computing

RESTful Web Service

3 Components:

1. URL (e.g., „http://serviceparrot.com/resources“)

2. Internet media type (JSON, XML/SOAP, YAML, JPG, AVI, etc.)

3. Operation set {GET, POST, PUT, DELETE}

REST examples:

- The World-wide Web

- Amazon S3

- Windows Azure

133 Cloud Computing

REST + WSDL (optional)

Src:http://en.wikipedia.org/wiki/Web_Services_Description_Language

134 Cloud Computing

Service/Client communication

Service Client Communication

Protocol

XML/SOAP

JSON

YAML

(homebrew)

?

135 Cloud Computing

Java Script Object Notation (JSON)

-Light-weight method exchange standard

-MIME Type: application/json

-Basic data types

- Number

- String

- Boolean

- Array

- object

136 Cloud Computing

JSON Sample (Menu)

And in XML…

cv

cv

Overhead!

137 Cloud Computing

Yet Another Markup Language (YAML)

-Designed to easily map to high-level data types

- (e.g., list, hash, scalar) very Perl‘ish!

- List

- [milk, pumpkin pie, eggs, juice]

- Hash

- {name: John Smith, age: 33}

- Scalar

- date: 2007-08-06

138 Cloud Computing

JSON, XML, YAML - Comparison

JSON XML YAML

Network bandwidth + - +

Processing performance - + (DOM) -

Human readability - + -

Schema validation - + (XSD) -

Partial processing - + -

139 Cloud Computing

REST Services - Summary (Chappell, 2009)

- REST defines no standard data representation

- RESTful service can use XML, JSON, and others

- Pros

- Data formats can better match clients

- (e.g., using JSON with JS clients)

- Different formats can be chosen to match different performance requirements

- Cons

- Options increase complexity

- RESTful services do not (necessarily) describe their interface

- Means more dependence on written documentation

140 Cloud Computing

REST Services - Summary (Chappell, 2009)

- Most developers don’t like writing raw HTTP calls

- Providing client library requires

- Choosing what language and environment to support

- Dealing with versioning

141 Cloud Computing

REST Services - Summary (Chappell, 2009)

- The semantics of PUT, GET, DELETE are well defined

- The semantics of POST are less clear

- From the HTTP 1.1 spec

142 Cloud Computing

SOAP vs. REST - Summary (Chappell, 2009)

- Calling SOAP-based services “Web Services” makes no sense

- SOAP has little to do with Web technologies

- REST-based services truly deserve the name Web Services

- They are entirely based on HTTP and URIs

- Choosing operations (SOAP) over resources (REST)

- SOAP and REST emphasize different things

- Capabilities

- SOAP/REST provide different functions

143 Cloud Computing

SOAP vs. REST - Summary (Chappell, 2009)

- REST

- Focused on named resources

- Each of which typically represents some data

- Every application exposes its resources through the same interface

- SOAP

- Focused on accessing named operations

- Each of which typically implements some logic

- Different applications expose different interfaces

144 Cloud Computing

A practical example (Chappell, 2009)

- A service for banking functions might include operations such as

- GetBalance(Account)

- UpdateBalance(Account, Amount)

- These work well with either REST or SOAP…

- Suppose interface also includes

- Transfer(FromAccount, ToAccount, Amount)

- This maps naturally to a SOAP operation

- It does not map well to the REST resource-oriented model

145 Cloud Computing

SOAP vs. REST - Caching (Chappell, 2009)

- For most services the majority of requests are reads

- In RESTful services all reads rely on HTTP GET

- Results of GET are commonly cached

- Can allow better performance and more scalability for RESTful services exposed over the Internet

146 Cloud Computing

SOAP vs. REST - Security (Chappell, 2009)

- RESTful services commonly use SSL

- Standards for carrying security tokens

- HTTP for username/password

- SSL for X.509 certificates

- This is sufficient for many scenarios

- (e.g., point-to-point Internet communications)

147 Cloud Computing

SOAP vs. REST - Security (Chappell, 2009)

- SOAP-based services can use SSL

- SOAP-based services can also use WS-Security, which provides

- Support for identity through SOAP intermediaries

- Not just point-to-point

- Broader standards for carrying security tokens

- A standard way to provide data integrity and data privacy

148 Cloud Computing

SOAP vs. REST - Transactions (Chappell, 2009)

- ACID transactions that span multiple applications are important in enterprise computing

- ACID transactions don‘t usually make sense across the Internet

- WS-AtomicTransactions addresses this problem

- It relies on WS-Coordination

149 Cloud Computing

SOAP vs. REST - Transactions (Chappell, 2009)

150 Cloud Computing

SOAP vs. REST - Reliability (Chappell, 2009)

- REST

- Assumes application deals with failures via retries

- SOAP with WS-ReliableMessaging

- Builds acknowledge/retry logic into the communications stack

- Can provide end-to-end reliability to one or more SOAP intermediaries

151 Cloud Computing

SOAP vs. REST Capability Summary (Chappell, 2009)

152 Cloud Computing

SOAP vs. REST – Make your Choice (Chappell, 2009)

- Neither is right for every situation

- Each has its place

- Some questions to ask

1. Does the service expose data or logic?

- REST can be a good choice for exposing data

- SOAP might be better for exposing logic

2. Does the service need the capability of W*, or is a simpler RESTful service sufficient?

3. What is best for the developers who will build clients for the service?

- The best decisions come from reasons, not emotion!

160 Cloud Computing

Lecture Announcement

Next semester: “Service Engineering”

Prof. Andreas Schmietendorf

(Master students only)

166 Cloud Computing

Literature

• SOAP vs REST – Complements or Competitors? (Chappell, 2009)

• RESTful Web Services vs. Big Web Services: Making the right Architectural Decision (Pautasso, 2008)

• BPM and SOA (Rosen, 2008)

• Object-oriented Web Services (Neumann & Baumann, 2010)

167 Cloud Computing

And now lean back after another tough lecture…

Java vs. Microsoft .Net