RPC RMI SOAP Presentation PDF

RPC RMI SOAP Lecturer: Dr. David Mguni www.qmul.ac.uk /QMUL @QMUL Queen Mary University of  Introduction When distributed systems were first utilised processes communicated by passing messages Messages only contained data The in...

RPC RMI SOAP Lecturer: Dr. David Mguni www.qmul.ac.uk /QMUL @QMUL Queen Mary University of  Introduction When distributed systems were first utilised processes communicated by passing messages Messages only contained data The interpretation of this message had to be agreed between the sender and receiver This makes it difficult to reuse www.qmul.ac.uk /QMUL @QMUL  Review: Sockets Socket: door between application process and end-end-transport protocol The API for applications to communicate applicatio across applicatio socket the network controlled by process n process n app developer transport transport network network controlled by OS link Internet link physical physical www.qmul.ac.uk /QMUL @QMUL 3  Review: Sockets and ports Logical resources managed by the operating system Sockets are always assigned a free port when created Each process on a networked host can be addressed remotely by the port number it is listening to TCP and UDP ports are independent For server-side applications, default port numbers are defined – HTTP -> 80 – HTTPS -> 443 – SMTP -> 25/QMUL www.qmul.ac.uk @QMUL 4  Introduction Technologies were introduced (beginning with Remote Procedure Call (RPC)) to make communication between distributed processes more uniform, reusable and user-friendly Essentially these technologies allow users to call functions on different physical machines as if they were local www.qmul.ac.uk processes /QMUL @QMUL  Remote Procedure Call (RPC) Proposed in the 1970s and first practically implemented in the early 1980s Earliest popular implementation on Unix system was Sun’s RPC in 1984 which was used to support the Network File System (NFS) Popular implementations today include: – XML-RPC – JSON-RPC www.qmul.ac.uk /QMUL @QMUL  Remote Procedure Call Goal of RPC is to allow (RPC) clients on different physical machines to call procedures as if they were calls to the local machine This is abstracted from the user so they make remote procedure calls in the same way that they make local calls The RPC implementation is responsible for – Connecting to the remote host – Sending the parameters – Performing the operation on the remote host – Returning the results www.qmul.ac.uk /QMUL @QMUL  Characteristics of RPC A familiar interface for application developers Allow the implementation of the request reply paradigm Includes a standard message format Includes a standard interface to allow the reuse of code www.qmul.ac.uk /QMUL @QMUL  Limitations of RPC Calls by reference are not possible as machines use a different address space Large object (classes) which might normally be passed by reference need to be copied May be byte ordering issues (Big Endian vs Little Endian) May be formatting issues (ASCII, UTF-8, UTF-16, UTF-32) www.qmul.ac.uk /QMUL @QMUL  Big Endian Vs Little Endian https://en.wikipedia.org/wiki/ Endianness www.qmul.ac.uk /QMUL @QMUL  RPC Procedure RPC is a request response protocol The procedure is initiated by a client who sends a request message to a known remote server to execute a specified function with the supplied parameters The remote server sends a response to the client and the procedure continues The client will wait for the response from the client unless an asynchronous request message www.qmul.ac.uk is sent to the server /QMUL @QMUL  RPC Events The events associated with an RPC are as follows: 1. The client contacts the client stub. As this is a local call parameters are pushed to the stack in the normal way 2. The client stub packs the parameters into a message. This is known as marshalling. The client stub then makes a system call to send the message 3. The client’s local operating system sends the message to the server 4. The server’s local operating system passes the message to the server stub 5. The server stub unpacks the parameters of the message. This is known as unmarshalling 6. The server /QMUL www.qmul.ac.uk stub calls the remote procedure. The reply uses the @QMUL same procedure in reverse  Compilation https://cseweb.ucsd.edu/classes/sp16/cse291-e/applications/ln/lecture3.html www.qmul.ac.uk /QMUL @QMUL  RPC Stub The stub is a gateway for distributed system objects and all outgoing requests to server-side objects that are routed through it It also includes network logic to ensure reliable communication between the client and the server It is responsible for: – Initiating communication with the server – Marshalling and unmarshalling messages – Informing the server that the procedure should be calledserver- side www.qmul.ac.uk /QMUL @QMUL  Marshalling Marshalling is the process of transforming the memory representation of an object into a format suitable for storage or transmission Parameters sent in an RPC call must be marshalled before they can be sent to the remote procedure Marshalling is also used in the.NET framework and in the Mozilla Application Framework www.qmul.ac.uk /QMUL @QMUL  Marshalling Example Consider a program which works in user space and kernel space To transition from user space to kernel space a system call is required This is a slow operation - can take microseconds to complete so the number of system calls should be minimised To minimise the number of system calls - a buffer of commands can be maintained in user space and in kernel space www.qmul.ac.uk /QMUL @QMUL  Marshalling Example (cont...) Commands waiting for execution are marshalled into the user space buffer When the kernel space buffer is nearly empty a system call is executed and commands in the user space buffer are transferred into the kernel space buffer This approach used in Linux’s OpenGL to minimise system calls when rendering www.qmul.ac.uk /QMUL @QMUL  Marshalling Example (cont...) www.qmul.ac.uk /QMUL @QMUL  Marshalling Vs Serialisation If you are using Python marshalling and serialisation are considered to the same thing More complicated in Java: Marshalling also records the codebases (location of object class definitions) Therefore, it treats remote objects differently and does more than serialisation www.qmul.ac.uk /QMUL @QMUL  RPC Failures Like other components in distributed systems there are many types of failures and it is very difficult to determine the cause of a failure (debug) If failure of an RPC occurs any one of the following situations could have occurred: – The action was successfully performed by the remote server but the reply was lost – The server dies before starting the work – The request never reaches the server – The client dies after it sends the request but before it receives the response www.qmul.ac.uk /QMUL @QMUL  RPC Success Modes This leads to different RPC success modes namely: – Exactly once: The RPC will execute once never more, never less. Expensive to implement but most like local calls – At most once: The client will only make one attempt to execute the RPC. If it works good, but if it fails the client will not attempt to repeat the RPC – At least once: The client will make multiple attempts to execute the RPC until it receives an acknowledgment even if the RPC executed on the remote host and acknowledgment of this was lost – Idempotent: www.qmul.ac.uk /QMUL The RPC @QMUL can be repeated without a change  XML-RPC This is an RPC implementation which uses XML to encode its calls and as its transport mechanism Calls can have multiple parameters and one result Parameters can be one of a few data types, but these data types can be complex (For example, an array of integers would be a complex data type) Can be used in multiple languages C++, www.qmul.ac.uk /QMUL @QMUL  JSON-RPC Very similar to XML-RPC but it uses JSON rather XML It also allows for notifications which are calls to the server that do not require a response It also allows for multiple calls to be sent to the server which can be answered out of order www.qmul.ac.uk /QMUL @QMUL  XML vs JSON XML is more verbose than JSON XML is more difficult to parse JSON represents data as a map rather than a tree This has led to criticism of XML-RPC (in the 2010s) www.qmul.ac.uk /QMUL @QMUL  Communication Over the Years gRPC (2015 - Now) Thrift (2008 – Now) Java – RMI (1997 – 2014) Rest API (2000 – Now) SOAP (1998 - Now) www.qmul.ac.uk /QMUL @QMUL  What do developers want? www.qmul.ac.uk /QMUL @QMUL  What do developers want? Do more application development, Do less communication www.qmul.ac.uk /QMUL @QMUL  Simple Open Access Protocol (SOAP) Initially designed as an Object Access protocol in 1998 Designers were also involved in the specification for XML-RPC The goal was to create a lightweight messaging format that works with any operating system, programming language and platform It also aimed to allow access of remote objects using non HTTP traffic through firewalls www.qmul.ac.uk /QMUL @QMUL  SOAP Characteristics The three main characteristics of SOAP are: – Extensibility (Other extensions such as security and addressing can be added to the original specification – Neutrality (SOAP can operate using any protocol such as HTTP, SMTP, TCP, UDP, or JMS) – Independence (SOAP can use any programming model) www.qmul.ac.uk /QMUL @QMUL  SOAP Processing Model Example www.qmul.ac.uk /QMUL @QMUL  SOAP extensibility model Designed to allow extensions to the framework which would alter the processing model. For example by including new information in the SOAP header new features such as reliability, security, correlation, routing and message exchange patterns could be included The extension must include the following – A URI must used to name the feature. – The information required at each node to implement the extension. – The processing required at each node to implement the extension including any handling of communication failure. – The information to be transmitted in the messages to allow the extension www.qmul.ac.uk /QMUL @QMUL  SOAP Envelope Example 5 www.qmul.ac.uk /QMUL @QMUL  SOAP Advantages and Advantages Disadvantages SOAP's neutrality characteristic explicitly makes it suitable for use with any transport protocol. SOAP, when combined with HTTP post/response exchanges, tunnels easily through existing firewalls and proxies Disadvantages When relying on HTTP as a transport protocol and not using Web Services Addressing or an Enterprise Service Bus, the roles of the interacting parties are fixed. Only one party (the client) can use the services of the other. The verbosity of the protocol and slow parsing speed of XML make it quite slow www.qmul.ac.uk /QMUL @QMUL  Modern SOAP Usage Use of through the WS-Security extension ACID-compliant SOAP is in decline as other alternatives (such as REST which we will discuss next week) have better performance There are some cases, however, where the usage of SOAP is preferred. SOAP can be used to achieve: – more robust security transactions with WS- Transaction and WS-Coordination www.qmul.ac.uk /QMUL @QMUL  Remote Method Invocation (RMI) RPC does not provide support for object abstraction Java’s RMI includes support for the direct transfer of serialised classes It also includes support for distributed garbage collection To achieve this a class must implement the Remote or UnicastRemote interface to make them Remote Objects www.qmul.ac.uk /QMUL @QMUL  Java Remote Objects Remote objects are the exact same as local objects in Java References are used to identify objects in Java Java applications will never possess the reference to the remote object A proxy object known as a stub is used to represent this object locally and the stub is responsible for marshalling of messages and their delivery in a similar fashion to RPC www.qmul.ac.uk /QMUL @QMUL  Remote Method Invocation (RMI) https://cseweb.ucsd.edu/classes/sp16/cse291-e/applications/ln/lecture3.html www.qmul.ac.uk /QMUL @QMUL  RMI Passing By Reference In Java all values are passed by reference rather than by value This is problematic with RMI To determine which objects can be passed by RMI Java uses the simple rule of only allowing objects which implement Remote to be passed To transfer objects Java uses the process of serialisation www.qmul.ac.uk /QMUL @QMUL  Java Serialisation https://www.geeksforgeeks.org/serialization-in- java/ www.qmul.ac.uk /QMUL @QMUL  Java Serialisation Serialisation is the conversion of the object to a Byte Stream which contains information on the class, the member variables, the type of the member variables and the values of this particular instance This allows the class to be recreated after it is transferred across the network We can use the following code to examine a Java Byte Stream www.qmul.ac.uk /QMUL @QMUL  Java Serialisation Example import java.io.*; import java.util.*; public class SerializationSample implements Serializable { private String aString = "The value of that string"; private int someInteger = 0; private transient List unInterestingLongLongList; public static void main( String [] args ) throws IOException { SerializationSample instance = new SerializationSample(); ObjectOutputStream oos = new ObjectOutputStream( new FileOutputStream(new File("o.ser"))); oos.writeObject( instance ); oos.close(); } } www.qmul.ac.uk /QMUL @QMUL  Java RMI Remote Interface Example package com.mkyong.rmiinterface; import java.rmi.Remote; import java.rmi.RemoteException; public interface RMIInterface extends Remote { public String helloTo(String name) throws RemoteException; } www.qmul.ac.uk /QMUL @QMUL  Java RMI Server Example package com.mkyong.rmiserver; import java.rmi.Naming; import java.rmi.RemoteException; import java.rmi.server.UnicastRemoteObject; import com.mkyong.rmiinterface.RMIInterface; public class ServerOperation extends UnicastRemoteObject implements RMIInterface{ private static final long serialVersionUID = 1L; protected ServerOperation() throws RemoteException { super(); } @Override public String helloTo(String name) throws RemoteException{ System.err.println(name + " is trying to contact!"); return "Server says hello to " + name; } public static void main(String[] args){ try { Naming.rebind("//localhost/MyServer", new ServerOperation()); System.err.println("Server ready"); } catch (Exception e) { System.err.println("Server exception: " + e.toString()); e.printStackTrace(); } } } www.qmul.ac.uk /QMUL @QMUL  Java RMI Client Example package com.mkyong.rmiclient; import java.net.MalformedURLException; import java.rmi.Naming; import java.rmi.NotBoundException; import java.rmi.RemoteException; import javax.swing.JOptionPane; import com.mkyong.rmiinterface.RMIInterface; public class ClientOperation { private static RMIInterface look_up; public static void main(String[] args) throws MalformedURLException, RemoteException, NotBoundException { look_up = (RMIInterface) Naming.lookup("//localhost/MyServer"); String txt = JOptionPane.showInputDialog("What is your name?"); String response = look_up.helloTo(txt); JOptionPane.showMessageDialog(null, response); } } www.qmul.ac.uk /QMUL @QMUL  Apache Thrift Created by Facebook Now an Apache Project Simple Interface Definition Language Efficient Serialisation in Space and Time- Variable Protocols Support for different Languages Code Generators for Glue Code Soft Versioning to allow interface and data type evolution between teams www.qmul.ac.uk /QMUL @QMUL  Apache Thrift From:; A.Prunicki, Thrift Overview, http://jnb.ociweb.com/jnb/jnbJun2009.html www.qmul.ac.uk /QMUL @QMUL  gRPC Developed at Google in 2015 Uses Google Protocol Buffers as the interface description language Protocol buffers are a flexible, efficient, automated mechanism for serialising structured data Similar to XML but smaller faster and simpler www.qmul.ac.uk/QMUL @QMUL  Google Protocol Buffers message Person { required string name = 1; required int32 id = 2; optional string email = 3; enum PhoneType { MOBILE = 0; HOME = 1; WORK = 2; } message PhoneNumber { required string number = 1; optional PhoneType type = 2 [default = HOME]; } repeated PhoneNumber phone = 4; } www.qmul.ac.uk /QMUL @QMUL  Google Protocol Buffers Person person; person.set_name("John Doe"); person.set_id(1234); person.set_email("[email protected]"); fstream output("myfile", ios::out | ios::binary); person.SerializeToOstream(&output); www.qmul.ac.uk /QMUL @QMUL  gRPC https://grpc.io/docs/guides/ www.qmul.ac.uk /QMUL @QMUL