Assigning a fix IP address to a VMware VM running on Windows machine and NAT networking.

I was trying to configure a two node hadoop cluster using ubuntu virtual machines created using VMWare Player [Running on Windows]. The setup worked fine in the beginning, but whenever the network adapter restarted [after VM resume/restart] it used to get a new IP address.

This causes multiple issues, those faced by me were specific to hadoop but any system that requires IP addresses to be entered in some sort of configuration will have to be reconfigured with new IP address each time they change.

Assigning static IP address to each VM is a solution, but I find it a bit time consuming method.There is an easier alternative, that can be done at only one place for all the VMs

VMware networking services running on the host system has a DHCP server, which is responsible for assigning IP addresses to guest machines. When guests are configured to obtain IP address automatically this service assigns them an unused IP from the pool.

Configuration for the DHCP server is maintained in following file :
C:\Documents and Settings\All Users\Application Data\VMware\vmnetdhcp.conf

Add one entry for each VM that needs to be given a fix IP address.

host ubuntu { hardware ethernet 00:0c:29:c0:2c:58; fixed-address 192.168.118.3; }

here host [ubuntu] is generally the name of .vmx file of your VM.
hardware ethernet can be found inside .vmx file as value of property "ethernet0.generatedAddress"
fixed-address is the IP address you wish to assign to your VM

Once you have entered information for all the nodes, VMWare DHCP service needs to be restarted.
If there are errors in your configuration, service will stop right after the restart.

Restart networking service on you guest VMs and your VM should get the desired IP address.

If you are finding it difficult to locate correct host and "hardware ethernet" open file vmnetdhcp.leasesX located at "C:\Documents and Settings\All Users\Application Data\VMware\".
A typical entry looks like this , there will be multiple such entries in the file

lease 192.168.118.142 {
    starts 3 2013/04/24 08:26:35;
    ends 3 2013/04/24 08:56:35;
    hardware ethernet 00:0c:29:c0:2c:58;
    client-hostname "ubuntu";
}

Go back to your VM and check which IP addresses is currently assigned to it. You can easily join this information to get all required parameters.

©2013 Abhijeet Apsunde LinkedIn

Having a website that loads faster is essential for great user experience. Many big and small hosting provider offer this service to their customers, but how do you make sure that you are really getting what you are paying for ? Are your users really experiencing faster page loads with a CDN ?

Lets start by understanding what a CDN is and how it works :

CDN integration helps load your content faster by mainly doing following

Terminate incoming connections from your users at data center physically closer to them, thereby reducing TCP and TLS connection overhead time dramatically.
Cache and serve static cacheable content closer to users so that it can be served quickly, this includes static html, css, javascript, images, fonts, videos etc.

How do I know it works for me ?

Scale and working of a CDN might be overwhelming for an average user let alone finding out if it has been effectively deployed for your website.
Best way to measure that effectiveness of your CDN integration is to see how your users see it !
This involves measuring your website load times wherever your users are, don't worry you don't have to get machines there , It has been already done for you !
Head to https://prober.tech/ and put the resource you want to test in the URL box. All times reports here are in millisecond.

This information is also available in tabular format for quick access / sorting
Looking at these numbers , total time taken to the main page for cloudflare.com appears uniform almost everywhere on the globe , which tells me that company that runs CDN for its customers also happened to have enabled it for their own website :)
Now let's look at the numbers for a site that I've hosted in Virginia, USA. In this example as you move physically away from the website (Virginia ) load times keep increasing. This is symptom of a website being served from one fixed physical location and doesn't have a CDN enabled.

Conclusion

With https://prober.tech/ you can measure your websites / resources load times from across the globe and get sense of how fast your users in or near those area perceive your website to be.

Introduction

In my last assignment I was asked to write a Java code that makes use of .Net DLLs. There are a lot of tools/libraries available on the web that will do this for you (JNI4Net actually works bi-directionally; you can call Java code from .Net code). But I wanted greater control over things so I decided to do it from scratch.

Assumption: I am assuming reader has basic knowledge of JNI programming. Like native methods in java code, generated header files and implementing the headers in native code.

Solutions

Most common way to solve this problem is to write a native code which invokes .Net code and uses this native wrapper in Java using JNI (This tutorial explains Native to .net part http://support.microsoft.com/kb/828736 ).For this thing to work, you should register your .Net assemblies using regasm.exe (tool that comes with Visual Studio).

But, there can be situations where you can’t use regasm.exe, in such case you can use registration free activation of .Net assemblies. (http://msdn.microsoft.com/en-us/library/ms973915.aspx). This procedure involves embedding registry information (that would have been written to registry by regasm.exe otherwise) in the DLLs. But I personally feel this approach is very complex and somehow didn’t work for me from JNI.

And when I thought I’m completely out of options, I met C++/CLI :)

C++/CLI is an entirely new language which is intended to supersede Managed Extensions for C++, you can find out more about this language at http://msdn.microsoft.com/en-us/magazine/cc163852.aspx

Why this is interesting because when you compile your C++/CLI code, generated code is a hybrid of native and managed code. And since you can code in C, C++/CLI and reuse managed library code in the same source file this becomes a lucrative option for our Java-Net connectivity bridge.

Tutorial

There are 3 different projects in this tutorial, You can download all these projects HERE.

A simple C# class library: Single class with one method that add two integers.
Java code which loads DLL created in project 3 to invoke functions implemented in C++/CLI code.
A C++/CLI library which uses C# library created in project 1 and implements JNI headers generated from Java native methods.

Part1: Simple C# library

Here, you can use any existing .Net library (.Net DLL) that you want to call from Java. I have included one for better understanding.

Create a C# project of type “Class library”.
My sample project includes single class which has a method that adds given two integers.

namespace MyCSharpMathsLib

{

public class Adder

{

public int addTwoNumberes(int a, int b)

{

return a + b;

}

Part2: Java code with native method.

This code is a simple Java class plus some native methods. You can directly import this project in Eclipse IDE and run CsharpConsumer.java once you have completed compiling and adding Proejct 3 DLLs to %PATH%

CsharpConsumer.java

public class CsharpConsumer {

static{

System.loadLibrary(“JNICsharpBridge");

//Load Project3 generated DLL, DLL’s parent folder should be in your libpath. [%PATH% variable], This will be executed at time of loading class CsharpConsumer

}

public static void main(String[] args) {

CsharpConsumer csc = new CsharpConsumer();

csc.reigsterAssemblyHandler("c:\\mydlls\\");

//Tell native code where to look for .net DLLs.

System.out.println("Result of adding = "+ csc.addTwoNos(1, 5));

}

native int addTwoNos(int a,int b);

native int reigsterAssemblyHandler(String str);

}

addTwoNos and reigsterAssemblyHandler are declarations of two native methods that we will implement in C++/CLI code.
“javah” tool generates C/C++ header files using compiled CsharpConsumer.java.
In order to use native code we must load native binaries into JVM process that’s done using System.loadLibrary call
In order to use .Net assemblies you must register corresponding DLLs to GAC (Global assembly cache) or the DLLs should be present in the same folder as that of your executables. But since our bridge DLL runs under JVM, these dlls should be copied to JRE\bin, and from deployment perspective this is an awkward situation. To overcome this problem we can load .Net assemblies that our code depends upon(MyCSharpMathsLib.dll in this case) dynamically from C++/CLI code
Native mothod “reigsterAssemblyHandler” does this job, and tells C++/CLI code where to look for dependencies (implemented in native code)

Part3: A C++/CLI library that acts as a bridge

This code acts as bridge between Java and C# (and managed code written in any language) code. C++/CLI has entirely new language syntax and I personally find it bit complex. But one major advantage of using C++/CLI is that here is that you can directly use managed objects and still your compiled binaries and accessible through native interfaces (e.g. JNI).

Create new CLR Console application.
From build settings make this project’s output type a DLL instead of exe, select /clr switch.
Include the files generated using “javah” in this project. Following snippet shows how to implement.
Add Project1 or its DLL as dependency / reference.
Implemented header file generated by javah utility.
Compile your code as a DLL and with “/clr” switch.
Put generated DLL in a directory that is listed in %PATH%, or put that directory in %PATH% variable, either ways possible, see what suits you.