Dynamic Deployment of IIOP-Enabled Components in the JBoss Server

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1 CD 2004 – Edinburgh, UK – May 2004Francisco Reverbel, Bill Burke, Marc Fleury

Dynamic Deployment of IIOP-Enabled Components in the JBoss Server

Francisco ReverbelCS Department, University of São Paulo

Bill BurkeJBoss, Inc.

Marc FleuryJBoss, Inc.


Outline� Introduction� JBoss Background

� JMX, Service Components, Meta-Level Architecture� The IIOP Module� Proxy Factories� IIOP Invoker and IOR Factory Internals� Related Work� Concluding Remarks

2


Introduction

• Introduction

• JBoss Background

• The IIOP Module• Proxy Factories

• IIOP Invoker and IOR Factory Internals

• Related Work

• Concluding Remarks


Software Components in the JBoss Server

� Application components� Server-side parts of distributed applications

� Middleware components� Provide middleware (system-level) services to

application components

Both kinds of components can be dynamicallydeployed into a running server

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Component Models� Application components follow J2EE standards

� EJB model: for business components (“enterprise beans”) whose methods can be invoked either by remote clients or by local clients

� Servlet/JSP model: for “web components”� Middleware components employ an extension

of the JMX model� This extension is JBoss-specific


IIOP-Enabled EJB Components� IIOP support is mandatory for EJB compliance

� IIOP support is a feature that can by dynamically added to a running server

� IIOP-enabled EJBs are dynamically deployable components themselves

� No extra compilation steps for IIOP stub/skeleton generation

� JBoss uses reflective techniques instead

JBoss supports IIOP in a dynamic way:

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Hot Deployment� Users can deploy IIOP-enabled EJBs into a

running server simply by dropping deployment units (such as EJB-JAR files) in the server’s deployment directory

� These deployment units contain no IIOP stubs and no IIOP skeletons

� They contain no JBoss-specific classes (such as EJB container or CORBA servant classes)

A change to a JBoss-specific deployment descriptor is all that is needed to

convert a non-IIOP-enabled deployment unit into an IIOP-enabled one


JBoss Background

• Introduction




• Related Work


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JMX Architecture

Java Virtual Machine

Agent Level InstrumentationLevel

MgmtClient

Browser

DistributedServices Level

Connector

ProtocolAdapter

AgentServices(as MBeans)

ManagedResources(as MBeans)

MBeanServer


The JMX component model� The instrumentation and agent levels define an

in-process component model� The MBean server provides a registry for JMX

components (MBeans)� Each MBean is assigned an object name that

is unique in the context of the MBean server� Clients use object names to refer to MBeans� MBean operation invocations always go

through the MBean server

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Method invocation on a dynamic MBean

Java Virtual Machine

Client

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MBeanRegistry

MBeanServer

MBean

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] The client holds no direct Java references to the MBean] It does not need to know the MBean’s Java class/interfaces] This very simple arrangement favors adaptation


Issues not covered by JMX^ Dependencies between MBeans^ Service lifecycle^ Packaging and deployment of MBeans

JBoss addresses these issues with the notions of service MBean and deployable MBean

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The JBoss model formiddleware components

� Service MBeans:� MBeans whose management interfaces include

service lifecycle operations� Also called service components

� Deployable MBeans:� Service MBeans packaged according to EJB-like

conventions, in deployment units called service archives (SARs)

� A SAR includes a service descriptor, an XML file that conveys information needed at deployment time

� Also called deployable services� They are a JBoss- specific extension to JMX


Meta-level architecture for EJB: the case of a non-IIOP client

Server Virtual Machine

MBeanServer

ContainerMBean

Server-SideInterceptors

EJBComponent

Client Virtual Machine

Client-SideInterceptors

InvocationHandler

DynamicProxy

EJB Client

InvokerProxy

EJBContainer

InvokerMBeanClient-Side

Proxy

Meta Level

Base Level

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Reified method invocations

� No interface along the reified invocation path depends on base-level application types

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Remote invocation architecture for non-IIOP clients (1 of 2)

Y EJB containers expose a type-independent LZ Q[ Y

\R]

NH*_ operation` Protocol-specific invoker MBeans make this

operation accessible to remote clients through various protocols (JRMP, HTTP, SOAP)

` Client-side stubs are dynamic proxy instances

` They convert calls to the typed interfaces seen by clients into LZ Q[ Y

\R]

NH*_ calls on remote invokers

ServerVM

MBeanServer

ContainerMBean

InvokerMBean

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Remote invocation architecture for non-IIOP clients (2 of 2)

� Each client-side proxy has an invocation handler that performs remote calls on a given invoker, over the protocol supported by the invoker

� Client side proxies and their invocation handlers are instantiated by the server and dynamically sent out to clients as serialized objects



InvocationHandler

DynamicProxy

EJB Client

InvokerProxy


Proxy

Meta Level

Base Level


JBoss invokers� Deployable MBeans that act as protocol-specific

gateways to multiple EJB containers� Interface exposed by the JRMP invoker:

� Other non-IIOP invokers implement either thisinterface or very similar ones

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Invoker proxies� A client-side proxy

(or, more precisely, its invocation handler) must “know a remote invoker”

� This knowledge is protocol-specific

� It is encapsulated within an invoker proxy



InvocationHandler

DynamicProxy

EJB Client

InvokerProxy


Proxy

Meta Level

Base Level


The IIOP Module

• Introduction




• Related Work


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The IIOP module consists of...

… three deployable MBeans:� &�

2�

5� %� $�

2�

U� E� 6� H U� YL��

FH �� Thin wrapper around a third-party IIOP engine� JacORB is the default IIOP engine in the JBoss

distribution� &�

R� U� E� D� 1� D� P�

L�

Q� J� 6H�� U� Y L�

F H� In-process CORBA naming service� Reuses (through inheritance) code from the

JacORB naming service� ,� ,� 2

�3� ,� Q� Y

�R� N� H� U


The IIOP invoker! Unlike all other invokers, it does not follow the

JBoss “invoker pattern”! IIOP is treated as an special case" Reason: interoperability with CORBA clients written

in other languages" The “invoker pattern” leads to an IIOP invoker that

expects IIOP requests with the verb LQYRNH in their operation fields

# But IDL-generated stubs send out IIOP requests whose operation fields contain application-specific verbs

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Meta-level architecture for EJB: the case of an IIOP client


MBeanServer

ContainerMBean

EJBComponent


EJBContainer

IIOP InvokerMBean

Meta Level

Base Level

CORBAServant

POA


EJBClient

IIOPStub

Server-SideORB

Client-SideORB

calls to base-level interfaces

calls to ORB-specific interfs.

IIOP request

call to OMG-defined interface

flow of reified invocations


Proxy Factories

• Introduction




• Related Work


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EJB references� An EJB reference is either a reference to an

(�

-� %� 2�

E� M� H� F� W or a reference to an (-%�� +� R�

P�

H�� EJB containers have the responsibility of creating such references, which in various situations they pass to EJB clients or to EJB implementations

� JBoss supports two general kinds of EJB references:� Java references to dynamic proxy instances, which

are sent out to other VMs as serialized Java objects� CORBA references, passed across process boundaries in the standard IOR format


The proxy factory interface

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Implementations of the EJBProxyFactory interface� 3�

U� R� [�

\�

)� D� F� W R�

U\� � Instances of this class create dynamic stubs that

talk to remote invokers over various protocols � 3�

U� R� [�

\�

)� D� F� W R�

U� \+��

$

Instances of this class create dynamic stubs used in clustered JBoss environments� The “HA” suffix stands for “high availability”

� ,� 2�

5� )� D� F� W R�

U\� � Instances of this class create CORBA references


Relationship between invokers, proxy factories and containers


MBeanServer

ContainerMBean

EJBComponent

EJBContainer

IIOP InvokerMBean

CORBAServant

POA


Server-SideORB

HTTP InvokerMBean

JRMP InvokerMBean

ProxyFactory

ProxyFactory

IORFactory

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Proxy factory configurations� EJB deployer MBean� Handles the deployment of EJB components� Reads container configurations from XML files and

creates containers� Container configuration� Has all the information the EJB deployer needs to

create a container MBean, its plug-ins and its interceptors

� Includes information on the container’s proxy factories� One proxy factory configuration per protocol


Information in a proxy factory configuration� The proxy factory class (a Java class)� The invoker MBean (the protocol!)� Additional parameters, depending on the proxy

factory class� In the case of non-IIOP access, XML elements in

the proxy factory configuration fully specify the chain of client-side interceptors

� No similar elements exist in the configuration of a proxy factory for IIOP access (,

�2�

5� )� DFW�� R�

U \� )

� Interceptors instantiated at the server side would not make sense for non- Java clients

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Global configuration file� Default container configurations for standard

kinds of EJBs:� Stateless session beans� Stateful session beans� Entity beans� Message-driven beansThese configurations support RMI over JRMP

� Alternative container configurations:� IIOP support� clustering� ...


Local configuration file� JBoss-specific deployment descriptor

� Optionally included with a given EJB� May refer to an alternative container

configuration by its name� Perhaps to specify other protocol, such as IIOP

� May fully define a new container configuration� May use a predefined configuration and

enhance it with aditional proxy factory configurations, also taken from the global configuration file

� EJB accessible via multiple protocols

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IIOP Invoker andIOR Factory Internals

• Introduction




• Related Work



CORBA servants� Two CORBA servants per IIOP-enabled EJB� home servant and bean servant� They must implement IDL interfaces not known in

advance!� Our servants use the stream-based ORB API� Each servant knows the object name of the target

container MBean� Each servant has marshalling knowledge specific to

the IDL interface it implements� Map from IDL operation names to ��

objects

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POA usage� Our choice of lifetimes for CORBA references:� Session bean instances : transient references� Entity bean instances : persistent references� EJB homes : persistent references� In terms of POAs:� Session bean servants are registered with POAs

with the TRANSIENT lifespan policy� Entity bean and home servants are registered with POAs with the PERSISTENT lifespan policy� These POAs may be per-servant or shared� Default: per- servant POAs created at deployment time


Lazy generation of RMI/IIOP stub classes (1 of 3)

� An ,2��

5� ) D F� W� R U� \� can be optionally associated

with a web class loader that generates RMI/IIOP stub classes in a lazy way� :�

HE�� &/��

is a subclass of URLClassLoader� It has a method � �� "!! #%$'&)(+*#%$'&)(,*�&&�$%-/.10$�-2.10)3354)-6-4)-6- 7�8'9768'9 ::; When a :<

HE=�> &?

/@ is asked to load )A RB

RBB�C

6D WXE�F EG , itH performs Java introspection on interface I IKJJ�JJL applies the Java to IDL mapping on I IMJJ'JJL uses code generation techniques to create a byte code array with the class file for NMO6O�PNMO�O,P/QQ5R�SR%S�TTU keeps this array in a hash map, to be returned by V VXWZYWZY5[[]\\+YYXWW+^^_ creates a ` `�a'b)cadb)c6cc instance from the byte code array

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� An in-process web server allows remote clients to download classes via HTTP

� A client downloads a class file by issuing an HTTP request to a resource name that includes� the id of a :

�H� E� &�

/� instance that can load the class� the full name of the class file

� When the web server receives such a request, it uses the :HE

��&� / given by the resource name

� to create a &�

OD�� V� V� object� to retrieve the corresponding class file



Default ,25�� )� D� FW�� R� U� \� configuration:� Every ,� 2� 5� )� D� F� W� R� U\� � has its :HE&/

�� instance� An ,2�� 5� )� D� F� W� R� U� \� includes information on its

web class loader in each IOR it generates� The IOR has a tagged component that specifies a

codebase URL for stub downloading� The path component in this URL identifies the web

class loader of the ,! 2"

5)#%$ D� F& W' RU(*) \+ that created the

IOR

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Related Work

• Introduction




• Related Work



Some related middleware systems

� Flexinet (Hayton et al)� Flexible remote invocation paths� Dynamic stubs

� OpenCOM (Clarke et al)� Lightweight component model� Based on a subset of COM� Dependence management, reconfiguration, method

call interception� Hadas (Ben-Shaul et al) � Fractal component model (Bruneton et al)

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Commercial J2EE servers� Most use compilation-based approaches� IONA’s ART framework

� relies on the chain of responsibility pattern� basis for various middleware products, including a J2EE

server� Nearly all commercial offerings require vendor-

specific EJB container or CORBA servant classes to be generated as part of the deployment process

� In the case of IIOP-enabled EJBs, all other servers require extra compilation steps for stub and skeleton generation


Concluding Remarks

• Introduction




• Related Work


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JBoss/IIOP... � Supports IIOP-enabled components without

sacrificing the levels of flexibility, developer friendliness and ease of use that JBoss had already reached in the non-IIOP case

� Strong reliance on reflection to make EJB deployment easy


Dynamic deployment issues... � Instantiation of CORBA servants for IDL

interfaces not known in advance� Creation of POAs at deployment time� Lazy generation of RMI/IIOP stubs

We believe that our techniques are equally applicable to CCM servers

and to other highly dynamic component environments.

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Thank you for your attention!� Q & A ...

Francisco [email protected]

Bill Burke Marc [email protected] [email protected]

http://www.jboss.org


Backup Slides

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Dynamic proxy usage� A dynamic proxy is an object adapter that

converts the type-independent interface of its invocation handler into a list of interfaces specified at runtime

� Dynamic proxies bridge the gap between the interfaces that are application-specific and those exposed by middleware components


The dynamic stub idiom� In Java RMI:

� Serializable types are normally passed by value� Remote types are normally passed by reference� What about a remote object that is also serializable?

� If it has not been exported through the RMI system, then it will be passed by value (in serialized form)

� This allows the creation of custom stubs, which interact over a custom protocol with the remote objects they represent

� JBoss uses dynamic proxies as custom stubs� The dynamic proxy implements application interfaces� Its customized part is the invocation handler

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Generalized EJB containers� A container MBean is created when an EJB is

deployed� It provides middleware services to its EJB

(instance pooling, instance caching, persistence, security, transactions...)

� … by merely aggregating aspects that do the real work

� Container configurations (XML files)� For standard kinds of EJBs� For JBoss-specific extensions� Customized containers for generalized EJBs


JBoss... � Demonstrates that application servers can be

built out of dynamically deployed components that provide middleware services to application components

� Brings reflective middleware to the world of mainstream computing

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Dynamic Deployment of IIOP-Enabled Components in the JBoss Server

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