Tag Archives: design pattern

Recent Hot Topics in Software Development

InfoQ, one of my favorite sites on software, recently posted an article Key Takeaway Points and Lessons Learned from QCon London 2012. If you missed the conference but are still interested in recent trends of software development, it’s definitely a great read.

I browsed through the article, and found several interesting points there including the comments on Spring framework that VMware bought in 2009. In the following, I just list a few interesting or surprising comments and tweets from the article. If you are interested who made the comments based on which session, just check the original article.

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Cloud Architecture Patterns: VM Template

Intent

Standardize new virtual machine provisioning with templates

Category:

Creational pattern

Problem

It’s been a pain to create new virtual machines with the right software installed and configured properly. You can always use tools like KickStart to automatically install the operating system and then install other software as needed. But configuring such an environment is not trivial, and it takes a long time from start to finish.

With the rise of virtualization, more virtual machines are provisioned (and decommissioned) than ever before. Installing each new virtual machine from scratch is not the ideal solution.

Solution

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Cloud Architecture Patterns: Cloud Broker

Intent

Provide a single point of contact and management for multiple cloud service providers and maximize the benefits of leveraging multiple external clouds.

Category

Structural

Motivation

When you are buying and selling stocks or other securities, you hire a broker to execute the trade on your behalf. One reason for that is convenience. You don’t need to take care of the details of placing orders and working with multiple stock exchanges, and whatever else is required to trade securities.

How about working with multiple cloud service providers? For sure, you can go online to any cloud provider as long as you have your credit card ready. But is the service provider the best fit for your requirements? Do you have a backup plan if you are not satisfied with your service provider? Can you easily switch among your service providers to minimize cost or maximize flexibility? If you are not sure, you may then need something like a cloud broker.

Solution

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Cloud Architecture Patterns: Service VM

Intent

Provide an easy way to provision new infrastructure and application services for a computing cloud

Category

Behavioral

Problem

To run a large-scale computing infrastructure, you will need many different types of services, including compute, storage, and networking, among others. After virtualization has successfully detached compute from the physical hardware, it’s very easy to provision and scale compute. But compute requires storage and networking which are lagging behind. To maximize the benefits of virtualization and cloud computing, it’s natural to push the storage and networking in the same direction.

Looking beyond the infrastructure to consider applications, we need various types of services such as database, directory, messaging, and more. I’ve covered the App VM pattern that allows using IaaS for PaaS in a previous blog. While you can pack some of these services into an application VM, the problem is that it scales well but does not follow the aspectual centralization pattern.

Solution

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Cloud Architecture Patterns: VM Pipeline

Intent

Provide a configurable structure for modularized information processing

Category

Structural

Problem

Complicated data processing involves many distinctive and repetitive steps. Each of these steps can be mapped to a software module that is independently developed and assembled for particular cases of data processing.

Given the elastic nature of cloud computing, it’s a perfect platform for data processing. We need a solution that is flexible in two ways:

1.     Modularized components for data processing;

2.     Configurable so that different modules can be re-used easily in various cases.

Solution

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Cloud Architecture Patterns: App VM

Intent

Provide packaged software stack as Platform-as-a-Service (PaaS) platform for running applications

Category

Behavioral

As Known As

PaaS VM

Motivation

We all know the three different types of cloud services from Infrastructure-as-a-Service (IaaS), PaaS, to Software-as-a-Service (SaaS). If you want to leverage PaaS, you have to choose one of the PaaS service providers like Google or Microsoft. Leveraging an external PaaS has its own benefits.

What if you want to keep your applications running in-house but still enjoy the benefits of PaaS? Today you don’t have much choice. Google, for example, does not sell its App Engine as a product that you can install and run on premise. You have to run it on the Google cloud.

Solution

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Cloud Architecture Patterns: Façade VM

Intent

Provide a single point of contact for a large-scale system consisting of many virtual machines so that they are viewed as one giant VM from outside

Category

Structural

As Known As

Giant VM

Motivation

When a system becomes big, you need multiple VMs to support the workload. For ease of use reasons, external users don’t want to manage multiple connections to each of the virtual machines. Who wants to remember a list of IP or DNS names for a service? Also, you just cannot expect your users to pick up the least-busy VMs for balanced workloads across your cluster of VMs. And to scale your application when your overall workload increases, you want a seamless way adding new capacities without notifying others.

Finally, if you offer a public service, you don’t want to allocate a public IP address for each of your VMs. These days, public IPs are scarce resources and may cost you money.

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Cloud Architecture Patterns: Stateless VM

Intent

Ensure a virtual machine does not carry a permanent state so that it can be easily provisioned, migrated, and managed in the cloud.

Also Known As

Disposable VM

Category

Behavioral

Motivation

Virtualization is the cornerstone for cloud computing, especially at the infrastructure level. With many virtual machines created, managing them becomes a big challenge.

Among these challenges are system provisioning, backup, archiving, and patching different virtual machines. These administrative tasks take lots of CAPEX and OPEX.

We need a better way to architect applications for the cloud.

Solution

Making a VM stateless solves a lot of problems. For one thing, you force applications to save data outside of the virtual machine. No longer do you need to back up the virtual machine – only the data. It also makes the system provisioning easier without differentiating the different instances. When the stateless VMs crash for whatever reasons, you don’t lose much. Just add a new virtual machine and voila!

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Cloud Architecture Patterns: Aspectual Centralization

Intent

Separate concerns in large scales computing by leveraging different types of services in the cloud

Category

Behavioral

Motivation

The history of computing reveals different eras starting from mainframe to client/server to Web computing. With mainframes, computing is contained within the boundary of a mainframe. With client/server and web computing we see the separation of the presentation from the data. With all these computing models, the data is owned and maintained by different applications. The IT staffs who run and maintain the applications are responsible for backing up and maintaining data.

With the rise of cloud computing, I see a new trend that will fundamentally change the game and push productivity to all new levels. I call this “Aspectual Centralization” (AC). This is as important to cloud architecture as Model-View-Controller (MVC) is to software architecture.

Solution

With AC, different aspects of an application are extracted out and delegated to centralized services: data services, messaging services, logging services, and so on.

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Cloud Architecture Patterns: VM Pool

Intent

Provide a mechanism to fast provision virtual machines (VMs) and manage their lifecycles by maintaining a pool of virtual machines.

Category

Creational

Motivation

Virtual machines can be expensive to create. It takes several minutes to create a new virtual machine. Technologies like linked clone and storage offloading can help speed up the process, but it still takes time. And these alternative approaches, in some use cases, do not help when you need instant provisioning.

Solution

It’s generally a good practice to pool resources that are expensive to create. In programming, you pool threads and check them out on demand. When it’s done, you check them in back to the pool. This is what most Web Servers do for high performance.

You can leverage the same idea for VM provisioning. You create new virtual machines and put them into a pool. When there is a new request, you just check out one virtual machine from the pool. The following diagram shows how it works.

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Cloud Architecture Patterns: VM Factory

In my last blog, I wrote about pattern idea from the famous books “Design Pattern” and “A Pattern Language” and how it can be applied to cloud architecture design. Below and in later posts in this series I shall follow the content outline used there to illustrate the cloud architecture patterns.

Intent

Provide a standard way to create new virtual machines based on user requirements.

Category

Creational

Motivation

There are enormous combinations of virtual machines with different operating systems, middleware, and applications. And then we have user data to the mix! We need a standard way to create new virtual machines.

General speaking, there are three basic ways to create new virtual machines:

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Cloud Architecture Patterns: Overview

Design patterns have been very popular among software developers since the book by Gang of Four (Enrich Gamma, Richard Helm, Ralph Johnson, John Vlissides) in 1995. If you go to an interview for a software engineering position today, the chances are you most likely get one or more questions on design patterns. 

Like many concepts in software that from other disciplines, the “pattern” idea was “borrowed” from “A Pattern Language,” a book by Christopher Alexander on architectural patterns published 20 years before we started to talk about software design pattern. His book turns out to be a great way to summarize and document reusable design elements for different engineering works.

As Christopher points out, “Each pattern describes a problem which occurs over and over again in our environment, and then described the core of the solution to that problem, in such a way you can use the solution a million times over, without ever doing it the same way twice.”

Today I “borrow” the same idea and apply the concept to cloud computing on architecture designs. The main focus is on virtual machine-based architecture patterns so that you can best leverage virtual machines for your cloud computing.

What is a Cloud Architecture Pattern?

An architectural pattern extracts the common and re-usable design concepts and components. If we put it in the big picture, it should be somewhere below the overall system architecture and above software design as the middle layer.

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