Software Architecture & Design
6CCS3SAD
Dr Kevin Lano
Session 10:
Clouds, Services, Microservices,
SOA
March 2022
Learning Outcomes
At the end of this session you should be able
to:
– Explain the purpose and functionalities of clouds, web
services, microservices and SOA
– Use our UML2 extension to specify SOA
3
Overview
•
•
•
•
•
Cloud
Service-oriented Architecture (SOA)
Web Services
Microservices
Containers
4
Cloud
• So far
– Application servers provide transparency for software
components
• What if we could also provide transparency
of hardware?
–
–
–
–
Resources as a commodity (rented, not purchased)
No need to know what HW your SW runs on
No need to know where that HW is
Let someone else manage the HW and share it with
other users
 Increased flexibility & economies of scale
5
Cloud software characteristics
• Scalability
– Increases in load/number of users can be handled by
increasing the number of (virtual) servers running new
copies of software
• Elasticity
– Also can scale down resources to match reduced
demand
• Resilience
– Tolerates server failures by dynamic re-allocation of
servers to tasks
6
Cloud Services
• Types of Cloud services
– Infrastructure-as-a-Service (IaaS)
– Platform-as-a-Service (PaaS)
– Software-as-a-Service (SaaS)
– Mobile Backend-as-a-Service (MBaaS)
7
Infrastructure-as-a-Service
(IaaS)
• Transparent infrastructure (i.e., HW)
– Physical machines (PMs) or virtual machines (VMs)
• Pay for additional resources as and when
needed
– Automated commissioning through an API or web
front end
• “Metered” consumption:
– Pay for what you use, so flexible for expansion
– No need for capital cost of buying hardware
• Examples: AWS, Microsoft Azure
8
Platform-as-a-Service (PaaS)
• IaaS plus a set of standardised services
– Data management, logging, email API,
payment services, …
• Build software more efficiently by
building on existing services
– Truly component-based thinking
– Reuse at a large scale
• Examples: Heroku, Google App Engine,
…
9
Software-as-a-Service (SaaS)
• “Rent” your software system
– Typically accessed through a web front end or app
– Data managed transparently on cloud servers
– Implementation shared across different users
• Highly efficient delivery model
– Provider keeps control of software and operations
– Efficient updates rolled out to all clients (or only a
selection of clients)
• Examples: Microsoft Office 365, Dropbox, …
10
Software-as-a-Service (SaaS)
Software
Customers
Software
Provider
Software Services
Cloud
Provider
Cloud Infrastructure
11
Software-as-a-Service (SaaS)
• Advantages for customers:
–
–
–
–
Access from any device
No up-front costs for software or servers
Immediate software updates
Reduced software management costs
• Disadvantages:
– Data held remotely (privacy & security issues)
– Loss of control over updates
– Service lock-in (need to keep paying to access
software even when not used)
12
Overview
•
•
•
•
•
Cloud
Service-oriented Architecture (SOA)
Web Services
Microservices
Containers
13
Service-oriented Architecture
•
•
•
•
•
•
•
•
A system structured as set of communicating services
Services are self-contained functional units
Minimise shared datastores
Communicate using standard protocols and data formats
(eg., XML, JSON)
Loosely-coupled, not aware of internals of other
services. Technology and location independent
Service discovery mechanisms are required, eg., via
registries of services/service brokers
Services can be composed, orchestrated, etc
Shifts complexity from application into network
14
SOA example
Holiday Booking Service
Car Rental Service
Hotel Booking Service
Holiday Package
Calculator
Flight Booking Service
Internal functionality of service
External services
15
Web Services
• Problem: various systems require integration
– written under heterogeneous platforms and languages
– Distributed over a network (eg., the internet)
• Solutions:
– Re-implement systems to operate under a common platform or
communication framework (costly)
– Implement connection points between systems as web services
(cheaper)
Java based
system
Webservice
client
HTTP
SOAP
Webservice
server
.NET based
system
16
Web Services
• Services published using a description language:
– Define name and parameters of service
Web service
directory
Locate a
web
service
Webservice
Client application
client
Register a web service
HTTP
SOAP
Webservice
server
Server
application
17
Web Services
• Web services are typically:
– Business-to-business or involve access to
remote data
– Can be a common subtask in several
business processes.
• Should not:
– Be performance-critical
– Require fine-grained interchange of data.
18
Web Services
• Web service host
– Machine on which web service executable
resides
• Publisher of a web service
– Makes web service available for use
• Consumer of a web service
– Application that uses web service
• 2 main approaches: SOAP; REST
19
Web Services
• SOAP: Simple object access protocol
– XML-based protocol for exchanging
messages, including descriptions of remote
procedure calls (RPC).
– SOAP messages are XML documents
(envelopes) describing method call of service.
Body can contain request or response data.
• WSDL: Web services definition
language
– XML-based descriptions of services
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SOAP Web Services
• Easy and flexible way of doing RPCs
– Components whose interfaces are exposed through
HTTP
– Client component obtains a proxy reference to the
web service and invokes methods on that
– Infrastructure transforms method invocations into
XML for transmission over the net
• Using the Simple Object Access Protocol (SOAP) and HTTP
21
REST & RESTful Web Services
• Representational State Transfer
(REST):
– Data & functionality accessed using Uniform
Resource Identifiers (URIs), resources/services are
identified by URIs, global addresses
– Uses only standard HTTP commands
– GET retrieves current state of a resource.
– POST transfers a new state onto a resource.
– Resources are decoupled from their representation so
their content can be accessed in variety of formats,
eg. HTML, XML, plain text, PDF, JPEG, JSON, and
others.
22
REST & RESTful Web Services
– Every interaction with a resource is stateless: request
messages are self-contained.
– Stateful interactions are based on concept of explicit
state transfer, eg., by using URI rewriting, cookies,
and hidden form fields.
– State can be embedded in response messages to
point to valid future states of the interaction.
• Compared to SOAP/WSDL approach, REST is
simpler (no special languages/formats needed) but
less flexible: clients must know precise URI of
service.
Java API for REST web services: https://github.com/jax-rs
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SOAP Web Services in .NET
using System;
using System.Web.Services;
using System.Xml.Serialization;
WebService attribute to indicate
service location
[WebService(Namespace="http://localhost/MyWebServices/")]
public class ExampleService : WebService {
[WebMethod]
public int Add(int a, int b)
Subclass WebService
{
return a + b;
}
[WebMethod]
public string SayHello()
{
return "Hello World";
}
WebMethod attribute indicates
methods to be exposed
}
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UML2 Specialization
• Treat web services like other components
– Add <<WebService>> stereotype
• Implies use of service through SOAP
– Tagged Values
• WebServiceNamespace to indicate service location
• WebMethod to indicate methods to be exposed
– Used on provided interface
<<Webservice>>
ExampleService
{WebserviceNamespace =
"http://localhost/
MyWebServices/"}
IMsg
{Webmethod=[add,sayHello]}
<<Interface>>
IMsg
+add(a:int,b:int):int
+sayHello():string
25
SOAP Web Services in Java EE
import java.util.*;
import javax.jws.WebService;
import javax.jws.WebMethod;
import javax.jws.WebParam;
WebService annotation
@WebService( name = “ExampleService", serviceName = “ExampleService" )
public class ExampleService
{ @WebMethod( operationName = “add" )
public int add(int a, int b)
{ return a+b; }
@WebMethod( operationName = “sayHello" )
public String sayHello()
{ return “Hello World"; }
}
WebMethod annotation indicates
methods to be exposed
JAX-WS specification: https://javaee.github.io/metro-jax-ws/
26
REST web service example
Share price predictor using Monte-Carlo simulation
REST web service example
• All data supplied as input parameters:
–
–
–
–
–
currentPrice : double
timeDays : int – length of period for prediction
growthRate : double
variation : double – volatility of the share
runs : int – number of samples to generate
• result parameter gives estimated future
price.
• For a web service, name of service changed
to estimateFuturePrice
REST web service example
Share price predictor input form
REST web service example
<jsp:useBean id="bean" scope="request" class="beans.ControllerBean"/>
<jsp:setProperty name="bean" property="currentPrice“ param="currentPrice"/>
<jsp:setProperty name="bean" property="timeDays" param="timeDays"/>
<jsp:setProperty name="bean" property="growthRate" param="growthRate"/>
<jsp:setProperty name="bean" property="variation" param="variation"/>
<jsp:setProperty name="bean" property="runs" param="runs"/>
<html><head><title>estimateFuturePrice</title></head>
<body>
JSP receives request, copies
<h1>estimateFuturePrice</h1>
<% bean.estimateFuturePrice(); %>
<h2>estimateFuturePrice performed</h2>
<strong> Result = </strong> <%= bean.getResult() %>
</body>
</html>
data to ControllerBean,
executes bean operation
and generates result web
page.
REST web service example
package beans;
import java.util.*;
public class ControllerBean
{ Controller cont;
ControllerBean wraps
implementation class
Controller
public ControllerBean() { cont = Controller.inst(); }
double currentPrice, growthRate, variation;
int timeDays, runs;
String result;
public void setcurrentPrice(String _s) { … convert _s to a double … }
public void estimateFuturePrice()
{ result = "" + cont.estimateFuturePrice(currentPrice, timeDays, growthRate,variation,runs); }
public String getResult() { return result; }
}
REST web service example
<<JSP>>
estimateFuturePrice
ControllerBean
Controller
Presentation Tier
Business Tier
32
REST web service example
Response to request estimateFuturePrice.jsp?
currentPrice=100 & timeDays=50 & growthRate=0.1 & variation=0.09
Service Pattern Examples
• Service Broker
– Define a service which locates services which
can meet a given request, and links such a
service to the requestor
• Service Decomposition
– Decompose a coarse-grained service into two
or more subservices
34
Service Broker
Client interface: Service
Search
Supplier services can register/deregister with Broker.
Client issues search for a particular functionality.
Broker
Broker finds suitable server service & connects
requestor and service (eg., by returning URI of service
to requestor).
<<publish/subscribe>>
Service3
Service1
Service2
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Service Broker Example
Client interface: Flight
Search
FlightBroker
Broker finds flight providers which can sell
the requested flights & connects
requestor to these providers
<<publish/subscribe>>
FlightProvider3
FlightProvider1
FlightProvider2
36
Microservices
• Architectural style
– SOA with fine-grained services
– Use services for componentisation of
applications
– Each running in its own process
– Potentially developed by separate teams
– Communication via web-based protocols
http://martinfowler.com/articles/microservices.html
Microservice Composition
• Orchestration
– One master service coordinates others in the
correct order
• Choreography
– Services coordinate with each other, by
generating and listening to events
Microservice Orchestration
• API gateway
– Provides access point for clients to possibly a
set of services
– The gateway selects the correct service and
translates service requests into calls to
individual services
• For example, several related financial
services could be managed in this way
– Share price estimation; option valuation;
trading advice, etc.
Orchestration example
Financial Services API
Presentation Tier
Business Tier
Option pricing
Share price estimator
Trading advisor
40
Choreography example
<<publish/subscribe>>
Requestor
BondPriceEstimator
YieldCurveService
<<publish/subscribe>>
To compute price of bond B, estimator requires a yield curve (map of time to interest rates)
for time period of B, when this is available, the BondPriceEstimator is notified, this reads any
required rates in order to compute the price of B.
In turn,
this price is delivered by notification to the original requestor.
03/03/2016
41
Microservices: Advantages
• Real-world componentisation!
– Independent modification
 Incremental updates of application functionality
– Clear boundaries of team responsibility
• Organisational impact
– Continuous deployment in an agile development
process
– Microservices enforce cross-functional teams rather
than functional silos
Microservices: Disadvantages
• Deployment
– More complex as there are more “moving parts”
– More skills and better tools needed
• Performance
– Need efficient cross-process communication
• Flexibility
– More difficult to move component boundaries
• Failure
– Any service can fail at any time
– Need more extensive monitoring and defensive programming
• Could be seen as a good thing 
• No explicit required interfaces
43
Microservices: Failure management
• Internal service failure
– Detected by service & reported to requestor
– HTTP error codes can be used (eg., 200 for success, 404 for
failure due to an unreachable resource)
• External service failure
– External cause prevents service from operating – actions
needed to restart service
• Service performance failure
– Degradation of service due to excessive loads, etc
– Address by monitoring and reconfiguration
– Eg., using a ‘circuit breaker’ which cuts an unresponsive service
out of the configuration of services.
https://martinfowler.com/bliki/CircuitBreaker.html
44
Overview
•
•
•
•
•
Cloud
Service-oriented Architecture (SOA)
Web Services
Microservices
Containers
45
Containers
• Use ideas from the Cloud to support
microservices
– Containers provide all software required for
specific microservices
– Lightweight virtualisation compared to full
VMs
– Require less resources and reduced
activation time compared to VMs
• Example tooling: Docker
https://www.docker.com/
Summary
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•
•
•
Cloud: IaaS, PaaS, SaaS
Service-oriented Architecture (SOA)
Web Services: SOAP, REST
Microservices: Composition &
management
• Containers
47