API First is a design strategy for a company’s entire product line, where APIs are the basis of every product instead of being a separate side product. To understand why API First is a good idea, you first have to understand how existing APIs are generally created. There are various models for creating APIs, but generally the API accesses the backend directly in parallel with the main product. This means that if you want to make new applications, you have to either write more systems that access the backend or extend the API so that it supports both alternative products. Additionally, an API is frequently considered to be an “extra, nice to have” product rather than an important member of the product ecosystem. This creates serious problems with resource contention as the API competes against revenue producing products for engineering resources. APIs as a Side Product Think first about an example of the “usual” setup for APIs – as you can imagine, the API is separate from the main product, and even if all secondary products run off of the API, there will be a mismatch between the two experiences. Keeping everything entirely consistent is theoretically doable but a lot more work than simply restructuring the infrastructure to treat the API as a piece of core technology for the system. There is some thought that separating out the API from the main product can protect that product from attacks via the API, but truthfully the backend system is the critical piece, and separating out the clients in this way simply makes it harder to triage and fix problems that might occur in the product or the API. Keeping everything in the same pipeline helps assure consistency, reliability and as your product grows, it makes scaling much easier. Imagine that a company has a product for creating and updating contact information for users. The backend returns lists of users based on a database call from the client. In this case, the main product communicates directly with the backend system, and is likely to retrieve data in a different way as a result. When the backend system team adds a new “Location” field feature, it doesn't show up in the API until an engineer has time to add it there. This means that there will be a necessary lag between the addition of this field to the main product and availability within the API until and unless someone takes the time to write essentially duplicate code to retrieve the new fields. There’s a lot of technical debt incurred when you have multiple systems trying to reproduce a single interface. There’s not likely to be a good process for comparing this API change to other APIs from the company – resulting in inconsistent results. In this case, the mobile app wouldn’t allow or see locations, resulting in developer dissatisfaction and customer confusion and irritation. Once you’ve established how you want your users to interact with your system, it’s best to support that everywhere. When you have multiple teams creating products without a shared vision, you also tend to have poor communication between those teams. This can lead to bug fixes in one code base but not in the other, or inconsistencies between the items available from the system depending on which interface is being used. API First Model The other possibility is an API First model. All of the products run off of the same interface. This ensures that each device, application or integration has the same resources available to use. These resources will be consistent across the entire product line. Note that just because an API resource is available within the system, you don’t have to expose it to all the world – you can decide which of the API resources is internal, partner only, or open to anyone. It’s still a great idea to have your API ready because when a major partner asks for access to some specific resources to support a use case, you have it ready to go. API First also encourages communication between your backend team and each of the client engineering teams. Understanding use cases at a high level the helps create APIs that are usable for the use cases you understand up front, and more likely to support future use cases that come up. Once you’re creating the API as a larger team, you’ll find many places where different teams offer complementary resources adding to a much better structured system. API First makes a lot of sense for any company – as soon as you have more than one product (for most companies that’s going to be a website and a mobile application) you need to have a layer to protect the clients from changes on the server. A well-documented interface into the system, crafted with specific use cases in mind, allows you the freedom to change things around on the backend, as long as the interface doesn’t change. Integrated testing is easier, and the products running on the API will by their nature test the integrity of the system on a regular basis. You can learn much more about APIs in my book Irresistible APIs, available from Manning Publications, Inc.

As developers, we are always looking for a better, faster way of doing things. Whenever I am learning a new language that typically runs in an IDE, then I begin to look for ways to test code snippets through either the Terminal for Mac or the command prompt on Windows. Swift is no exception. As I’ve been working more and more with this language, I’ve uncovered four ways to quickly test Swift code that are not only great for your day-to-day job, but can be used to collaborate and help others learn this new language. #1 : REPL (Read-Eval-Print-Loop) Xcode’s debugger includes an interactive version of the Swift language, known as the REPL (Read-Eval-Print-Loop). This allows you to try out the Swift language within LLDB in Xcode’s console, or from Terminal. If you have at least Xcode 6.1 or higher, then you can simply open your terminal and type: swift You can also invoke it with the following commands on earlier versions of Xcode 6 : xcrun swift lldb --repl It looks like the following: This is great for quick code snippets that you might want to try without launching Xcode. #2 : Swift playgrounds Swift playgrounds are a way to compile and run Swift code live as you type. The results of each line are presented in a timeline as they execute, and variables can be inspected at any point. Playgrounds are typically created as a standalone project (as the image below indicates), but they can be created within an existing Xcode project as well. There are plenty of sample playgrounds out there, and you are free to usemine to get started. Below you will see an example of the timeline in action, providing a visual look of arrays, for loops and more. The obvious reason to use Swift playgrounds is the rich editor that includes syntax highlighting, code completion and more. The disadvantage is that you have to open Xcode in order to do so. #3 : Using an Online Editor SwiftStub has become one of the most popular ways to compile and run Swift code on the fly without requiring a Mac. All you need is a web-browser open to SwiftStub and off you go. It includes the functionality that you would expect, such as a custom URLs and uploading or saving a playground, but it also supports team collaboration. You can easily add people to your current Swift project and even add audio and group chat if neccessary. #4 : Using iTerm2 with Guard-shell This is my preferred environment, but it is geared towards power users that don’t mind spending a few extra minutes setting it up. Don’t worry if you have never done this before as I’ll walk you through the process, step-by-step. I prefer to use iTerm2. Think of it as a replacement for the Terminal app on Mac. In the words of the authors, “iTerm2 brings the terminal into the modern age with features you never knew you always wanted.” I’ve been using it for a couple of months and couldn’t agree more. We are also going to use the help of Guard-shell to automatically run shell commands when watched files are modified. In this case, we’ll be watching files with the .swift extention. Once you have these applications downloaded, you only need to remember a few commands to get started… Within iTerm2, press ⌘D to get a Vertical Split and ⇧⌘D for a horizontal split. Navigate to your home directory and type: vim Guardfile Once you are inside the Guardfile, you will need to switch to “Insert” mode. Simply type the following and when you are finished press “esc” and then type :w to save the file. Type :x to save and exit vim. source 'https://rubygems.org' gem 'guard-shell' You will now have a file named Gemfile and it is time to install the gem. Simply type: bundle install You should then see the following: Fetching gem metadata from https://rubygems.org/............ Fetching version metadata from https://rubygems.org/.. Resolving dependencies... Using hitimes 1.2.2 Using timers 4.0.1 Using celluloid 0.16.0 Installing coderay 1.1.0 Using ffi 1.9.8 Installing formatador 0.2.5 Using rb-fsevent 0.9.4 Using rb-inotify 0.9.5 Using listen 2.9.0 Installing lumberjack 1.0.9 Installing nenv 0.2.0 Installing shellany 0.0.1 Installing notiffany 0.0.6 Installing method_source 0.8.2 Installing slop 3.6.0 Installing pry 0.10.1 Installing thor 0.19.1 Installing guard 2.12.5 Installing guard-compat 1.2.1 Installing guard-shell 0.7.1 Using bundler 1.8.5 Bundle complete! 1 Gemfile dependency, 21 gems now installed. Now would be a good time to create a directory where you want guard-shell to be monitoring for .swift files that have changed. I created a folder called Swift, then ran the following command : bundle exec guard init shell A new file called Guardfile will be created in that folder. Now type vim Guardfile, enter the following lines and save the file the same way you did before. guard :shell do watch(/(.*).swift/) do |m| puts puts puts puts "Running #{m[0]}" puts `swift #{m[0]}` end end Finally type: bundle exec guard If everything worked successfully, then Guard-shell will inform you that it is watching a folder as shown below: Switch over to your left-hand panel and make sure you are in the folder that Guard is watching and type “vim test.swift” and type the following Swift code: var first = "hello" var second = "world" println("\(first) \(second)") Use :w to save the file and see the output in the right-hand panel as shown below. Wrap-up Hopefully you can find a solution that works for your development process out of the four options that I presented today. I assume that, since you are interested in testing Swift code snippets, you are building Swift apps as well. You may be interested in my article on how to build a task app in Swift as well. In addition, Telerik provides several powerful UI componentsfor iOS such as Charts, Calandar, ListView and more. Thanks for reading and sound off in the comments below with your ideal environment.

a few days ago, visual studio 2015 rc was released. among the many updates to .net framework 4.6 with this release, we now have some new utility methods allowing conversion to/from unix timestamps. although these were added primarily to enable more cross-platform support in .net core framework , unix timestamps are also sometimes useful in a windows environment. for instance, unix timestamps are often used to facilitate redis sorted sets where the score is a datetime (since the score can only be a double ). unix timestamp conversion before .net 4.6 until now, you had to implement conversions to/from unix time yourself. that actually isn’t hard to do. by definition , unix time is the number of seconds since 1st january 1970, 00:00:00 utc. thus we can convert from a local datetime to unix time as follows: var datetime = new datetime(2015, 05, 24, 10, 2, 0, datetimekind.local); var epoch = new datetime(1970, 1, 1, 0, 0, 0, datetimekind.utc); var unixdatetime = (datetime.touniversaltime() - epoch).totalseconds; we can convert back to a local datetime as follows: var timespan = timespan.fromseconds(unixdatetime); var localdatetime = new datetime(timespan.ticks).tolocaltime(); unix timestamp conversion in .net 4.6 quoting the visual studio 2015 rc release notes : new methods have been added to support converting datetime to or from unix time. the following apis have been added to datetimeoffset: static datetimeoffset fromunixtimeseconds(long seconds) static datetimeoffset fromunixtimemilliseconds(long milliseconds) long tounixtimeseconds() long tounixtimemilliseconds() so .net 4.6 gives us some new methods, but to use them, you’ll first have to convert from datetime to datetimeoffset. first, make sure you’re targeting the right version of the .net framework: you can then use the new methods: var datetime = new datetime(2015, 05, 24, 10, 2, 0, datetimekind.local); var datetimeoffset = new datetimeoffset(datetime); var unixdatetime = datetimeoffset.tounixtimeseconds(); …and to change back… var localdatetimeoffset = datetimeoffset.fromunixtimeseconds(unixdatetime) .datetime.tolocaltime();

This is a short post about a method I recently discovered in Guava. The Issue I had a situation at work where I was working with objects structured something like this: public class Outer { String outerId; List innerList; ....... } public class Inner { String innerId; Date timestamp; } public class Merged { String outerId; String innerId; Date timestamp; } My task was flatten a list Outer objects (along with the list of Inner objects) into a list of Merged objects. Since I’m working with Java 7, using streams is not an option. The First Solution Instead I turn to the FluentIterable class from Guava. My first instinct is to go with the FluentIterable.transform method (which is essentially a map function): List originalList = getListOfObjects(); Function> flattenFunction //Details left out for clarity //returns an Iterable of Lists! Iterable> mergedObjects = FluentIterable.from(originalList).tranform(flattenFunction); But I really want a single collection of Merged objects, not an iterable of lists! The missing ingredient here is a flatMap function. Since I’m not using Scala, Clojure or Java 8, I feel that I’m out of luck. A Better Solution I decide to take a closer look at the FluentIterable class and I discover the FluentIterable.transformAndConcat method. The transformAndConcat method applies a function to each element of the fluent iterable and appends the results into a single iterable instance. I have my flatMap function in Guava! Now my solution looks like this: List originalList = getListOfObjects(); Function> flattenFunction //Details left out for clarity Iterable mergedObjects = FluentIterable.from(originalList).transformAndConcat(flattenFunction); Conclusion While this is a very short post, it goes to show how useful the Guava library is and how functional programming concepts can make our code more concise.

[This article appears in the DZone Guide to Performance & Monitoring – 2015 Edition. For additional information including insight from industry experts and luminaries, performance statistics and strategies, and an overview of how modern companies are handling application monitoring, download the guide below.] I have spent the last few years of my career working in the field of high-performance, low-latency systems. Two observations struck me when I returned to working on the metal: Many of the assumptions that programmers make outside this esoteric domain are simply wrong. Lessons learned from high-performance, low-latency systems are applicable to many other problem domains. Some of these assumptions are pretty basic. For example, which is faster: storing to disk or writing to a cluster pair on your network? If, like me, you survived programming in the late 20th century, you know that the network is slower than disk, but that’s actually wrong! It turns out that it’s much more efficient to use clustering as a backup mechanism than to save everything to disk. Other assumptions are more general and more damaging. A common meme in our industry is “avoid pre-optimization.” I used to preach this myself, and now I’m very sorry thatI did. These are just a few supposedly obvious principles that truly high-performance systems call into question. For many developers, these rules of thumb appear reasonably inviolable in everyday practice. But as performance demands grow increasingly strict, it becomes proportionally important for developers to understand exactly how systems work—at both the abstract, procedural level, and the level of the metal itself. MOTIVATION: THE REPERCUSSIONS OF INEFFICIENT SOFTWARE First, let’s think about why it’s important to transcend crude oversimplifications like “disk I/O is faster than network I/O.” One motivation is a bit negative. I can think of noother field of human endeavor that tolerates thelevels of inefficiency that are normal in our industry.My experience has been that for most systems, any performance specialist can improve its performance ten-fold quite easily. This is because most applications are hundreds, thousands, even tens of thousands of times less efficient than they could be. Modern hardware is phenomenally capable, but we software folks regularly underestimate the strides hardware manufacturers have made. As a result, we often fail to take advantage of new hardware capabilities and miss significant shifts in the locations of common performance bottlenecks. You may say this doesn’t matter—after all, what is all that hardware performance for, if not to make it easier to write software? And then I’ll reply: it’s for lots of things. Here’s one very concrete reason. The energy consumption from data centers constitutes a significant fraction of the CO2 being pumped into our atmosphere [1]. If most software is more than 10x less efficient than it could be, then that could mean 10x more CO2. It also means 10x the capital cost in hardware required to run all that inefficient software. “You don’t have to be an engineer to be be a racing driver, but you do have to have Mechanical Sympathy.” – Jackie Stewart, racing driver Perhaps more important is that performance is about more than just efficiency for its own sake. Performanceis also an important enabler of innovation. The ability to pack the data representing 1000 songs onto the tiny hard disk in the first generation iPod made it possible for Apple to revolutionize the music industry. For an even more basic example, graphical user interfaces only became feasible when the hardware was fast enough to “waste” all that time drawing pretty pictures. High-performance hardware enabled these innovations; the software simply had to follow. Then there’s the opportunity cost. What could we be doing with all the spare capacity of our astonishingly fast hardware and enormously vast storage if we weren’t wasting it on inefficient software? In the problem domains where I’ve worked, the idea of mechanical sympathy has helped enormously. Let’s examine this idea a little closer. KEY CONCEPT: MECHANICAL SYMPATHY The term Mechanical Sympathy was coined by racing driver Jackie Stewart and applied to software by Martin Thompson. Jackie Stewart said, “You don’t have to be an engineer to be be a racing driver, but you do have to have Mechanical Sympathy.” He meant that understanding how a car works makes you a better driver. This is just as true for writing code. You don’t need to be a hardware engineer, but you do need to understand how the hardware works and take that into consideration when you design software. Let’s take something simple like writing a file to disk. Disks are random access, right? Well, not really. Disks work by encoding data in sectors and addressing them in segments of the disk. When you read or write data to disk, youneed to wait for the heads to move to the correct physical location. If you do this randomly, then you will incur performance penalties as the heads are physically moved across the surface of the disk and you wait for the spin of the disk to place the sector you want beneath the read/ write heads. This averages out to about 3ms per seek for the heads, and about 3ms rotational latency. That makes for an average total of about 6ms per seek! This seek time is dramatically slow when compared tothe electronic. Electrons beat spinning rust every time! And there are even more specific reasons why “random access” is a poor rule of thumb. In fact, modern disks are optimized to stream data so that they can play movies and audio. If you understand that, and treat your file storage as a serial, block device rather than random access, you will get dramatically higher performance. In this example, the difference can be two orders of magnitude (200MB/s is a good working figure for the upper bound). REACHING HIGH PERFORMANCE: DO EXPERIMENTS, DO ARITHMETIC Abstraction is important. It is essential that we are, to some degree, insulated from the complexity of the devices and systems that form the platform upon which our software executes. However, many of the abstractions that we take for granted are very poor and leaky. The overall system complexity gets amplified when we build abstraction on top of abstraction to hide the problems caused by the leakiness, resulting in the dramatic performance differences we see between high-performance and “normal” systems. You don’t need to model or measure your entire systemto tackle its complexity. The starting point is to do some experimenting to understand your theoretical maximums. You should have a rough model of the following: How much data you can write to disk in one second How many messages your code can process in one second How much data you can send or receive across your network in one second A common meme in our industry is, “avoid pre- optimization.” I used to preach this myself. I am now very sorry that I did. The idea here is to measure your actual performance against the theoretically possible performance of your system within the limits imposed by the underlying hardware. Let’s consider a specific example. I recently talked witha developer who believed he was working on a high- performance system. He told me that his system was working at 10 transactions per second. As of mid-2015, modern processors on commodity hardware can easily perform 2-3 billion instructions per second. So at 2-3 billion instructions per second, the developer was limited to 200- 300 million instructions per transaction ([10 transactions/ sec] / [2-3G instructions/sec] = 200-300m instructions/ transaction) to achieve his goals. Of course, his application isn’t responsible for all of these—the operating system is chewing some cycles too—but 200 million instructions is an awful lot of work. You can write an effective chess player in 672 bytes, as David Horne has shown. Okay, so maybe the bottleneck was I/O. Perhaps this developer’s application was disk bound. That’s unlikely— modern hard disks found in commodity hardware can transfer data at phenomenal rates. A moderate transfer rate from disk to a buffer in memory is about 10MB/s. If this is the limit, he must be pushing more than 10MB per transaction between disk and memory. You can represent a lot of information in 10 million bytes! Well, perhaps the problem was the network. Probably not—10Gbit/s networks are now on the low end. A 10Gbit/s network can transmit roughly 1GB of data per second.This means that each of our misguided developer’s 10 transactions per second is occupying 1/10th of a GB, or approximately 100MB—more than 10 times the throughput of our disks! The hardware wasn’t the problem. HIGH PERFORMANCE SIMPLICITY I: MODEL THE PROBLEM DOMAIN One of the great myths about high-performance programming is that high-performance solutions are more complex than “normal” solutions. This is just not true.By definition, a high-performance solution must do the most amount of work in the fewest instructions. Complex solutions precisely don’t last long in high-performance systems because complexity is where performance bottlenecks hide. The best programmers I know achieve the simplicity demanded by high-performance systems by modeling the problem domain. A software simulation of the problem domain is the best way to come up with an elegant solution. HIGH PERFORMANCE SIMPLICITY II: SIMPLIFY THE CODE If you follow the lead of the problem domain, you tend to end up with smaller, simpler classes with clearer relationships. If you follow strong separation of concerns as a guiding principle, then your design will push you in the direction of cleaner, simpler code. The cardinal rule of object-oriented simplicity is “one class, one thing; one method, one thing.” Modern compilers are extremely effective at optimizing code, but they are best at optimizing simple code. If you write 300-line methods with multiple for-loops, each containing several nested if-conditions throwing exceptions all over the place and returning from multiple points, then the optimizer will simply give up. If you write small, simple, easy to read methods, they are easier to test and easier for the optimizer to understand, which results in significant improvements to performance. One of the great myths about high- performance programming isthat high-performance solutions are more complex than “normal” solutions. This is just not true. THE KEY TO HIGH PERFORMANCE: MINIMIZE INSTRUCTIONS, MINIMIZE DATAFundamentally, developing high-performance systemsis simple: minimize the number of instructions being processed and the amount of data being shunted around. You achieve this by modeling the problem domainand eliminating nonessential complexity. For software developers, “Mechanically Sympathizing” with modern high-performance hardware will help you understand where you’re doing things wrong. It can also point you in the direction of better measurement and profiling, which will help you understand why your code is not performing to its theoretical maximum. So why not try to save your company some money, work in a simplified codebase,and maybe help reduce the carbon footprint of our data centers—all at the same time? [1] https://energy.stanford.edu/news/data-centers-can-slash-co2-emissions-88- or-more DOWNLOAD YOUR FREE COPY TODAY

There's a misconception that DevOps is killing developers, but its not, it is killing the idea of server and IT operations maintenance.

Nowadays, there is a great demand for software development out there. The world needs software solutions for just about anything.

A key to improving performance is benchmarking. Read about Microsoft Diskspd's tools for storage and server benchmarking, and boost your I/O performance.

Wondering why the Eclipse Project view might not show all files in the Project Explorer view? For example it shows this: Eclipse Project Explorer View But on disk I have more files? Where are they? :idea: I’m using Eclipse Luna (4.4) in this post, but things are very similar for earlier versions of Eclipse. File System has more Files? Checking the files on my file system (e.g. with the Windows Explorer), I have more files/folders listed: Files on the File System Obviously, files and folders starting with a dot (‘.’) are not shown in the Project Explorer view. Project View Filters The reason is that the Eclipse Project Explorer view has a filter built-in to hide files. There is a setting for this in the View Menu of that view: Project Explorer View Menu There is a ‘Customize View…‘ menu item: Customize Project Explorer View And here I have the filters: Customize Project Explorer View Now it should be clear why the files starting with a dot are ont shown: they are filtered out with the filter for “.*”: Project Explorer View Filters Un-checking that filter will show now as well the dot files: Showing Dot Files in Project Explorer View Defining my own Filters The list of filters in the project view is provided by the plugins. And unfortunately there is no way to define my own filters in the above dialog, unless I would implement my Java plugin. Defining my own filters without programming things is possible, it is just in a different place:-). For example I do not want to see that ‘ProjectInfo.xml’. For this, I select the project and use the ‘Properties’ menu. Inside the project properties, there is Resource > Resource Filters: Resource Filters Use the Add button to add a new filter: Adding Filter To exclude just the ProjectInfo.xml: Exclude all (this will exclude all files matching my filter) Applies to Files (I only want to have it applied to files) [Name] [matches] the file name Excluding Files With that, I can build any kind of filters. Pressing OK, and it gets added to my filter list: Added Filter Now the ProjectInfo.xml is not listed any more in the Project Explorer view: Filtered ProjectView.xml Summary The Eclipse Project Explorer view has a setting to turn on/off filters for files/folders, or in general to configure the view. I can use project resource filters to define my own filters too. Happy Filtering :-)

For those of you who don’t know, It Was Never a Dress is to start a much-needed conversation about the underrepresentation of women in the tech industry.

What is Node.js? Ryan Dahl, and other developers, at Joyent created Node.js. Node.js is an open source, cross-platform runtime environment for server-side and networking applications. It brings event-driven programming to web servers enabling development of fast web servers in Javascript. In an event-driven application, there is a main loop that listens for events, and then triggers a callback function when one of those events is detected. Node.js also provides a non-blocking I/O API that optimizes an application's throughput and scalability. In a non-blocking language, commands execute in parallel, and use callbacks to signal completion. In a blocking language, commands execute only after the previous command has completed. Node.js uses the Google V8 JavaScript engine to execute code, and a large percentage of the basic modules are written in JavaScript. Node.js contains a built-in library to allow applications to act as a Web server without software such as Apache HTTP Server or IIS.NPM is the pre-installed package manager for the Node.js server platform. It is used to install Node.js programs from the npm registry. The package manager allows publishing and sharing of open-source Node.js libraries by the community, and simplifies installation, updating and un-installation of libraries. What are some of the Benefits of Node.js? 1. Asynchronous I/O It's built to handle asynchronous I/O from the ground up and is a good match to a lot of common web- and network-development problems. In addition to fast JavaScript execution, the real magic behind Node.js is called the Event Loop. To scale to large volumes of clients, all I/O intensive operations in Node.js are performed asynchronously. 2. Javascript Node.js is Javascript. So the same language can be used on the backend and frontend. This means it breaks down the boundaries between front- and back-end development. 3. Community Driven In addition to it’s innate capabilities, Node.js has a thriving open source community which has produced many excellent modules to add additional capabilities to Node.js applications. One of the most famous is Socket.io, a module to manage persistent connections between client and server, enabling the server to push real-time updates to clients. Socket.io abstracts the technology used to maintain these connections away from the developer, automatically using the best technology available for a particular client (websockets if the browser supports it, JSONP or Ajax longpolling if not). References: https://blog.udemy.com/learn-node-js/ http://pettergraff.blogspot.com/2013/01/why-node.html

The best way to write to a Cassandra cluster are concurrent asynchronous writes. In cases where data exhibits strong temporal locality, speed can be improved.

Besides, Android Studio platform developers also use Eclipse to develop applications, but always thought of Eclipse like a "Student-Project IDE " and learned about it.

In this article I will go through a common set-up for a small production environment. A single tier, load balanced application server cluster. Overview A high level overview of what we will be doing. Downloading and installing Apache HTTP server and mod_jk Downloading Tomcat Downloading Java Configuring two local Tomcat servers Clustering the two Tomcat servers Configuring Apache to use mod_jk to forward request to Tomcat Deploying application to Tomcat server that tests our set-up Introduction What is Apache? Apache is an HTTP server. What is mod_jk? It is an Apache module that allows AJP communication between Apache and a back end application server like Tomcat.I am running this on Ubuntu 14.04LTS installed on a dual boot PC with Windows 7. Download Apache2 We are going to use Ubuntu's APT package maintenance system to obtain and install Apache2. sudo apt-get install apache2 This will install in /etc/apache2 Download and install mod_jk The mod_jk module is not included in the Apache2 download so must be obtained and installed separately. The installation requires that the mod_jk module is visible to Apache and configured to ensure that Apache knows where to look for it and what to do with the requests you want to proxy. sudo apt-get install libapache2-mod-jk This will install in /etc/libapache2-mod-jk also two files have been added to the /etc/apache2/mods-available folder. Downloading and installing Tomcat 8 At the time of writing this Tomcat 8 does not have a package in APT so you must download the binaries from the tomcat website.http://tomcat.apache.org/download-80.cgi select the appropriate binary distribution and extract it as follows. tar xvzf apache-tomcat-8.0.5.tar.gz We need two copies of the Tomcat server to be load balanced. I created two directories in the /opt/ location: /opt/tomcat-server1/ and /opt/tomcat-server2/ and copied tomcat into each one. Download and install Java Download Java from APT as follows: apt-get install openjdk-7-jdk and set JAVA_HOME in .bashrc vim ~/.bashrc export JAVA_HOME=/usr/lib/jvm/java-7-openjdk-amd64 Configure two local Tomcat servers We will edit only the server.xml of the server2 installation of tomcat. We need to change port numbers to avoid conflicts.We change the following: and comment out the HTTP Connector as we only want the web application to be accessible through the load balancer.Here is my server2 Tomcat server.xml configuration. Configure mod_jk Load balancing is configured in the workers.properties file, located /etc/libapache2-mod-jk/ where workers represent actual or virtual workers.We will define two actual workers and two virtual workers which map to the Tomcat servers. In the worker.list property I have defined two virtual workers: status and loadbalancer, I will refer to these later in the Apache configuration.Workers for each server have been defined using values for the server.xml configuration files. I used the port values for the AJP connectors and I have included an lbfactor that sets the preference that the load balancer will show for that server.Finally we define the virtual workers. The loadbalancer worker is set to type lb and set the workers that represent the Tomcat servers in the balancer_workers properties. The status only needs to be set to type status. worker.list=loadbalancer,status worker.server1.port=8009worker.server1.host=localhostworker.server1.type=ajp13 worker.server2.port=9009worker.server2.host=localhostworker.server2.type=ajp13 worker.server1.lbfactor=1worker.server2.lbfactor=1 worker.loadbalancer.type=lbworker.loadbalancer.balance_workers=server1,server2 worker.status.type=status Ensure that you remove any other worker configuration that are not being used. Configure Apache Web Server to forward requests You will need to add the following to the Apache configurations located in etc/apache2/sites-enabled/000-default.conf JkMount /status status JkMount /* loadbalancer Verify the installation To test that all has been configured correctly we need to deploy an application. A sample application that has been used for years to test such configurations is called the ClusterJSP sample application. You can find it by googling in or from the JBoss site.Now deploy the war to the webapps folder on both servers and start each server using the start-up script /opt/tomcat-server1/bin/startup.sh.Go to http://localhost/clusterjsp/HaJsp.jsp and you should see the page show HttpSession information. Now lets look at the mod_jk status page: http://localhost/status. You will see that this page shows information about the load balancer workers and the workers it is balancing. If everything is working you will see the worker error state show OK or OK/IDLE if they are not currently balancing load. Things to try out Enable sticky sessions: Configure jvmRoute in the server.xml configuration. Further reading Loadbalancing with mod_jk and ApacheWorking with mod_jk Connecting Apache's Web Server to Multiple Instances of Tomcat

I find myself needing to take a PDF, output it at a specific size, and have the result offset to the top right hand side of the screen. To achieve it, I needed a few new switches to my good friend PDFJam, so I thought I'd share my command! pdfjam --suffix converted --papersize '{1920px,1080px}' --scale 0.4 --trim "-6cm -1cm 13cm 8cm" slides.pdf The --suffix is instead of giving an output filename, whatever you feed in ends up with the suffix in its filename. This is very handy because I use this command in a script and only need to pass in one variable. The --papersize isn't a switch I have used before either but you can set exact sizes for the final output which is nice. The --trim switch can also be used to set --clip=true to remove the trimmed space from the document if desired. I find PDFJam a very handy tool but with not nearly enough blog posts and code snippets around, so I'm dropping my command for future reference (yours as well as mine!).

I'm working on a mechanism that will allow HPCC to access data stored in Cassandra with data locality, leveraging the Java streaming capabilities from HPCC.

Learn about swim-lane diagrams to connect business processes and departments and apply the concept to the object-oriented world of javascript.

Learn more about trunk-based development and its influence on source control management systems, DevOps, and software development as a whole.

In this post, we learn how to combine JavaScript and RegEx to create scripts that can help us test our password strength.

Meteor itself does not rely on REST APIs, but it can easily access data from other services. This article is an excerpt from the book Meteor in Action and explains how you can integrate third-party data into your applications by accessing RESTful URLs from the server-side. Many applications rely on external APIs to retrieve data. Getting information regarding your friends from Facebook, looking up the current weather in your area, or simply retrieving an avatar image from another website – there are endless uses for integrating additional data. They all share a common challenge: APIs must be called from the server, but an API usually takes longer than executing the method itself. You need to ensure that the result gets back to the client – even if it takes a couple of seconds. Let’s talk about how to integrate an external API via HTTP. Based on the IP address of a visitor, you can tell various information about their current location, e.g., coordinates, city or timezone. There is a simple API that takes an IPv4 address and returns all these tidbits as a JSON object. The API is called Telize. Making RESTful calls with the http package In order to communicate with RESTful external APIs such as Telize, you need to add the http package: meteor add http While the http package allows you to make HTTP calls from both client and server, the API call in this example will be performed from the server only. Many APIs require you to provide an ID as well as a secret key to identify the application that makes an API request. In those cases you should always run your requests from the server. That way you never have to share secret keys with clients. Let's look at a graphic to explain the basic concept. A user requests location information for an IP address (step 1). The client application calls a server method called geoJsonforIp (step 2) that makes an (asynchronous) call to the external API using the HTTP.get() method (step 3). The response (step 4) is a JSON object with information regarding the geographic location associated with an IP address, which gets sent back to the client via a callback (step 5). Using a synchronous method to query an API Let’s add a method that queries telize.com for a given IP address as shown in the following listing. This includes only the bare essentials for querying an API for now. Remember: This code belongs in a server-side only file or inside a if (Meteor.isServer) {} block. Meteor.methods({ // The method expects a valid IPv4 address 'geoJsonForIp': function (ip) { console.log('Method.geoJsonForIp for', ip); // Construct the API URL var apiUrl = 'http://www.telize.com/geoip/' + ip; // query the API var response = HTTP.get(apiUrl).data; return response; } }); Once the method is available on the server, querying the location of an IP works simply by calling the method with a callback from the client: Meteor.call('geoJsonForIp', '8.8.8.8', function(err,res){ console.log(res); }); While this solution appears to be working fine there are two major flaws to this approach: If the API is slow to respond requests will start queuing up. Should the API return an error there is no way to return it back to the UI. To address the issue of queuing, you can add an unblock() statement to the method: this.unblock(); Calling an external API should always be done asynchronously. That way you can also return possible error values back to the browser, which will solve the second issue. Let’s create a dedicated function for calling the API asynchronously to keep the method itself clean. Using an asynchronous method to call an API The listing below shows how to issue an HTTP.get call and return the result via a callback. It also includes error handling that can be shown on the client. var apiCall = function (apiUrl, callback) { // try…catch allows you to handle errors try { var response = HTTP.get(apiUrl).data; // A successful API call returns no error // but the contents from the JSON response callback(null, response); } catch (error) { // If the API responded with an error message and a payload if (error.response) { var errorCode = error.response.data.code; var errorMessage = error.response.data.message; // Otherwise use a generic error message } else { var errorCode = 500; var errorMessage = 'Cannot access the API'; } // Create an Error object and return it via callback var myError = new Meteor.Error(errorCode, errorMessage); callback(myError, null); } } Inside a try…catch block, you can differentiate between a successful API call (the try block) and an error case (the catch block). A successful call may return null for the error object of the callback, an error will return only an error object and null for the actual response. There are different types of errors and you want to differentiate between a problem with accessing the API and an API call that got an error inside the returned response. This is what the if statement checks for – in case the error object has a response property both code and message for the error should be taken from it; otherwise you can display a generic error 500 that the API could not be accessed. Each case, success and failure, returns a callback that can be passed back to the UI. In order to make the API call asynchronous you need to update the method as shown in the next code snippet. The improved code unblocks the method and wraps the API call in a wrapAsync function. Meteor.methods({ 'geoJsonForIp': function (ip) { // avoid blocking other method calls from the same client this.unblock(); var apiUrl = 'http://www.telize.com/geoip/' + ip; // asynchronous call to the dedicated API calling function var response = Meteor.wrapAsync(apiCall)(apiUrl); return response; } }); Finally, to allow requests from the browser and show error messages you should add a template similar to the following code. Query the location data for an IP Look up location {{#with location} {{#if error} There was an error: {{error.errorType} {{error.message}! {{else} The IP address {{location.ip} is in {{location.city} ({{location.country}). {{/if} {{/with} A Session variable called location is used to store the results from the API call. Clicking the button takes the content of the input box and sends it as a parameter to the geoJsonForIp method. The Session variable is set to the value of the callback. This is the required JavaScript code for connecting the template with the method call: Template.telize.helpers({ location: function () { return Session.get('location'); } }); Template.telize.events({ 'click button': function (evt, tpl) { var ip = tpl.find('input#ipv4').value; Meteor.call('geoJsonForIp', ip, function (err, res) { // The method call sets the Session variable to the callback value if (err) { Session.set('location', {error: err}); } else { Session.set('location', res); return res; } }); } }); As a result you will be able to make API calls from the browser just like in this figure: And that’show to integrate an external API via HTTP!