Amazon’s Elastic Compute Cloud (EC2). EC2 is a web service that provides resizable, on-demand computing capacity — literally, servers in Amazon’s data centers — that you use to build and host your software. It’s important to understand that EC2 is a virtual computing environment. In a virtual environment, there is one physical server with all of the necessary hardware — CPU, memory, hard disk, network controller and more. This single physical server can host multiple operating systems and applications through a hypervisor that runs directly on top of the physical machine. The following simplified diagram shows a hypervisor architecture based on the Xen project: Xen interfaces directly with the hardware, and has a special control domain (dom0) for interfacing with Xen. Domain 0 is designed to access hardware directly and manage devices and device drivers. It has the ability to talk to the hypervisor to instruct it to start and stop guest VMs. ...

I first learned Vim in university and, since then, it has been a welcome companion for the majority of my software engineering career. Working with Python and Go programs felt natural with Vim and I was always felt productive. Yet Java was always a different beast. Whenever an opportunity to work with Java came up, I would inevitably try Vim for a while, but fall back to IntelliJ and the IdeaVim plugin to take advantage of the rich language features a full-featured IDE can give you. ...

Practical distributed applications are deployed into varied environments and execute on a variety of different machines linked together over a variety of communication infrastructure. The physical machines themselves can differ in the number and speed of processors, the availability of random access and stable storage, and more. The communication infrastructure can differ in the available levels of latency, throughput, and reliability. Because of these differences, it is more practical to look at distributed algorithms from a higher-level perspective so that they are applicable to a wide range of environments. Such algorithms do not depend on the particular details of the hardware or software on which they are run, and they are not limited to a highly specialized implementation. ...

A central tenet of databases is that any committed data survives a crash or a failure. Write-ahead logging is a fundamental primitive that ensures all changes to data are first written safely to stable storage before being applied. Coupling that with some careful use of sequence numbers and we can guarantee that changes made to a database can survive system crashes. Motivation Let’s start with a simple transaction T1 that reads object A, and updates the value for A with a write. To simplify matters, A is stored on disk as a single page as in Figure 1. ...

Every so often I get stuck with a running process that’s using a specific port, preventing me from running some new application that uses the same port. Then I’m left Googling for solutions or rebooting the machine to make progress. But not any more! I’m recording the solution for my future self (and of course for you, dear reader). > sudo lsof -i :<PortNumber> # returns list of processes using the port, with PID > kill -9 <PID> # kill the specific pid For example, you can find out what’s running on port number 8080 by running the command: ...

When people describe progress, they often describe it in terms of a linear progression taking us from primitive to advanced — an idea or invention occurs as a singular event, and somewhere further down the line of time a new idea or invention completely replaces it, relegating the old to the annals of history. This viewpoint is exemplified by traditional worldviews that organize all beings according to a chain of evolution, sometimes called the “great chain of being” (or scala naturae). The chain of being links God, angels, humans, animals, plants, and minerals in a hierarchy. All beings on earth, animate and inanimate, could be organized according to an increasing scale of perfection, from mushrooms and rocks at the bottom up through lobsters and rabbits, all the way to human beings and God at the top. ...

In the book “Thinking in Systems”, Donella Meadows dedicates an entire chapter to explaining why functioning systems seem to work so well. In it, she recognizes three characteristics: resilience, self-organization, and hierarchy. Resilience We can use the standard definition from the Oxford English dictionary to describe resilience: re·sil·ience /rəˈzilyəns/ noun the capacity to recover quickly from difficulties; toughness. “the often remarkable resilience of so many British institutions” the ability of a substance or object to spring back into shape; elasticity. “nylon is excellent in wearability and resilience” According to Donella Meadows this definition can be translated to systems as the “ability to survive and persist within a variable environment. The opposite of resilience is brittleness or rigidity.” ...

Java was the first programming language I was taught at University, and the language I used for the first decade of my career. It continues to be a reliable companion throughout my software development career. Unfortunately, not having developed with Java professionally for several years, I’ve found there are many aspects of the modern Java language that I’m simply not familiar with. To rectify this, I’ve collected the major improvements to the language beginning with Java 8, combined with a short explanation of how they work and how to use them. It assumes you know Java, but don’t really know Java. Hopefully, it can take you from experienced beginner to just plain experienced again. ...

One of the core features of modern Java is lambda expressions. Introduced in Java 8, lambdas provide concise syntax allowing the deferred execution of a block of code. Put a different way, lambdas allow us to pass behaviour as a method parameter. When the method executes, the lambda expression is run. This capability is often referred to as behaviour parameterization. Behaviour parameterization can be achieved in a number of ways, of which lambda expressions are usually the most convenient, and they are definitely the most concise. But what is behaviour parameterization, and why would we want to use it? To motivate this discussion, let’s work through a real-world example of filtering a list of items according to some criteria. More concretely, let’s investigate the problem filtering a list of students to find the ones with the best grades. ...

As a software system scales it becomes sufficiently large that the number of working parts, coupled with the number of working programmers making changes on it, makes the behaviour of the system extremely difficult to reason about. This complexity is exacerbated by the transition of many organizations towards a microservice architecture, as exemplified by the so-called “death star” architecture, where each point in the circumference of the circle represents a microservice and the lines between services represent their interactions. ...