|By AppDynamics Blog||
|February 12, 2014 01:18 PM EST||
The biggest difference between cloud-based applications and the applications running in your data center is scalability. The cloud offers scalability on demand, allowing you to expand and contract your application as load fluctuates. This scalability is what makes the cloud appealing, but it can’t be achieved by simply lifting your existing application to the cloud. In order to take advantage of what the cloud has to offer, you need to re-architect your application around scalability. The other business benefit comes in terms of price, as in the cloud costs scale linearly with demand.
Sample Architecture of a Cloud-Based Application
Designing an application for the cloud often requires re-architecting your application around scalability. The figure below shows what the architecture of a highly scalable cloud-based application might look like.
The Client Tier: The client tier contains user interfaces for your target platforms, which may include a web-based user interface, a mobile user interface, or even a thick client user interface. There will typically be a web application that performs actions such as user management, session management, and page construction. But for the rest of the interactions the client makes RESTful service calls into the server.
Services: The server is composed of both caching services, from which the clients read data, that host the most recently known good state of all of the systems of record, and aggregate services that interact directly with the systems of record for destructive operations (operations that change the state of the systems of record).
Systems of Record: The systems of record are your domain-specific servers that drive your business functions. These may include user management CRM systems, purchasing systems, reservation systems, and so forth. While these can be new systems in the application you’re building, they are most likely legacy systems with which your application needs to interact. The aggregate services are responsible for abstracting your application from the peculiarities of the systems of record and providing a consistent front-end for your application.
ESB: When systems of record change data, such as by creating a new purchase order, a user “liking” an item, or a user purchasing an airline ticket, the system of record raises an event to a topic. This is where the idea of an event-driven architecture (EDA) comes to the forefront of your application: when the system of record makes a change that other systems may be interested in, it raises an event, and any system interested in that system of record listens for changes and responds accordingly. This is also the reason for using topics rather than using queues: queues support point-to-point messaging whereas topics support publish-subscribe messaging/eventing. If you don’t know who all of your subscribers are when building your application (which you shouldn’t, according to EDA) then publishing to a topic means that anyone can later integrate with your application by subscribing to your topic.
Whenever interfacing with legacy systems, it is desirable to shield the legacy system from load. Therefore, we implement a caching system that maintains the currently known good state of all of the systems of record. And this caching system utilizes the EDA paradigm to listen to changes in the systems of record and update the versions of the data it hosts to match the data in the systems of record. This is a powerful strategy, but it also changes the consistency model from being consistent to being eventually consistent. To illustrate what this means, consider posting an update on your favorite social media site: you may see it immediately, but it may take a few seconds or even a couple minutes before your friends see it. The data will eventually be consistent, but there will be times when the data you see and the data your friends see doesn’t match. If you can tolerate this type consistency then you can reap huge scalability benefits.
NoSQL: Finally, there are many storage options available, but if your application needs to store a huge amount of data it is far easier to scale by using a NoSQL document store. There are various NoSQL document stores, and the one you choose will match the nature of your data. For example, MongoDB is good for storing searchable documents, Neo4J is good at storing highly inter-related data, and Cassandra is good at storing key/value pairs. I typically also recommend some form of search index, such as Solr, to accelerate queries to frequently accessed data.
Let’s begin our deep-dive investigation into this architecture by reviewing service-oriented architectures and REST.
REpresentational State Transfer (REST)
The best pattern for dividing an application into tiers is to use a service-oriented architecture (SOA). There are two main options for this, SOAP and REST. There are many reasons to use each protocol that I won’t go into here, but for our purposes REST is the better choice because it is more scalable.
REST was defined in 2000 by Roy Fielding in his doctoral dissertation and is an architectural style that models elements as a distributed hypermedia system that rides on top of HTTP. Rather than thinking about services and service interfaces, REST defines its interface in terms of resources, and services define how we interact with these resources. HTTP serves as the foundation for RESTful interactions and RESTful services use the HTTP verbs to interact with resources, which are summarized as follows:
GET: retrieve a resource
POST: create a resource
PUT: update a resource
PATCH: partially update a resource
DELETE: delete a resource
HEAD: does this resource exist OR has it changed?
OPTIONS: what HTTP verbs can I use with this resource
For example, I might create an Order using a POST, retrieve an Order using a GET, change the product type of the Order using a PATCH, replace the entire Order using a PUT, delete an Order using a DELETE, send a version (passing the version as an Entity Tag or eTag) to see if an Order has changed using a HEAD, and discover permissible Order operations using OPTIONS. The point is that the Order resource is well defined and then the HTTP verbs are used to manipulate that resource.
In addition to keeping application resources and interactions clean, using the HTTP verbs can greatly enhance performance. Specifically, if you define a time-to-live (TTL) on your resources, then HTTP GETs can be cached by the client or by an HTTP cache, which offloads the server from constantly rebuilding the same resource.
REST defines three maturity levels, affectionately known as the Richardson Maturity Model (because it was developed by Leonard Richardson):
Properly use the HTTP verbs
Thus far we have reviewed levels 1 and 2, but what really makes REST powerful is level 3. Hypermedia controls allow resources to define business-specific operations or “next states” for resources. So, as a consumer of a service, you can automatically discover what you can do with the resources. Making resources self-documenting enables you to more easily partition your application into reusable components (and hence makes it easier to divide your application into tiers).
Sideline: you may have heard the acronym HATEOAS, which stands for Hypermedia as the Engine of Application State. HATEOAS is the principle that clients can interact with an application entirely through the hypermedia links that the application provides. This is essentially the formalization of level 3 of the Richardson Maturity Model.
RESTful resources maintain their own state so RESTful web services (the operations that manipulate RESTful resources) can remain stateless. Stateless-ness is a core requirement of scalability because it means that any service instance can respond to any request. Thus, if you need more capacity on any service tier, you can add additional virtual machines to that tier to distribute the load. To illustrate why this is important, let’s consider a counter-example: the behavior of stateful servers. When a server is stateful then it maintains some client state, which means that subsequent requests by a client to that server need to be sent to that specific server instance. If that tier becomes overloaded then adding new server instances to the tier may help new client requests, but will not help existing client requests because the load cannot be easily redistributed.
Furthermore, the resiliency requirements of stateful servers hinder scalability because of fail-over options. What happens if the server to which your client is connected goes down? As an application architect, you want to ensure that client state is not lost, so how to we gracefully fail-over to another server instance? The answer is that we need to replicate client state across multiple server instances (or at least one other instance) and then define a fail-over strategy so that the application automatically redirects client traffic to the failed-over server. The replication overhead and network chatter between replicated servers means that no matter how optimal the implementation, scalability can never be linear with this approach.
Stateless servers do not suffer from this limitation, which is another benefit to embracing a RESTful architecture. REST is the first step in defining a cloud-based scalable architecture. The next step is creating an event-driven architecture.
Deploying to the Cloud
This paper has presented an overview of a cloud-based architecture and provided a cursory look at REST and EDA. Now let’s review how such an application can be deployed to and leverage the power of the cloud.
Deploying RESTful Services
RESTful web services, or the operations that manage RESTful resources, are deployed to a web container and should be placed in front of the data store that contains their data. These web services are themselves stateless and only reflect the state of the underlying data they expose, so you are able to use as many instances of these servers as you need. In a cloud-based deployment, start enough server instances to handle your normal load and then configure the elasticity of those services so that new server instances are added as these services become saturated and the number of server instances is reduced when load returns to normal. The best indicator of saturation is the response time of the services, although system resources such as CPU, physical memory, and VM memory are good indicators to monitor as well. As you are scaling these services, always be cognizant of the performance of the underlying data stores that the services are calling and do not bring those data stores to their knees.
The above graphics shows that the services that interact with Document Store 1 can be deployed separately, and thus scaled independently, from the services that interact with Document Store 2. If Service Tier 1 needs more capacity then add more server instances to Service Tier 1 and then distribute load to the new servers.
Deploying an ESB
The choice of whether or not to use an ESB will dictate the EDA requirements for your cloud-based deployment. If you do opt for an ESB, consider partitioning the ESB based on function so that excessive load on one segment does not take down other segments.
The importance of segmentation is to isolate the load generated by System 1 from the load generated by System 2. Or stated another way, if System 1 generates enough load to slow down the ESB, it will slow down its own segment, but not System 2’s segment, which is running on its own hardware. In our initial deployment we had all of our systems publishing to a single segment, which exhibited just this behavior! Additionally, with segmentations, you are able to scale each segment independently by adding multiple servers to that segment (if your ESB vendor supports this).
Cloud-based applications are different from traditional applications because they have different scalability requirements. Namely, cloud-based applications must be resilient enough to handle servers coming and going at will, must be loosely-coupled, must be as stateless as possible, must expect and plan for failure, and must be able to scale from a handful of server to tens of thousands of servers.
There is no single correct architecture for cloud-based applications, but this paper presented an architecture that has proven successful in practice making use of RESTful services and an event-driven architecture. While there is much, much more you can do with the architecture of your cloud application, REST and EDA are the basic tools you’ll need to build a scalable application in the cloud.
The post Architecting for the Cloud written by Dustin.Whittle appeared first on Application Performance Monitoring Blog from AppDynamics.
Cloud computing is changing the way we look at IT costs, according to industry experts on a recent Cloud Luminary Fireside Chat panel discussion. Enterprise IT, traditionally viewed as a cost center, now plays a central role in the delivery of software-driven goods and services. Therefore, companies need to understand their cloud utilization and resulting costs in order to ensure profitability on their business offerings. Led by Bernard Golden, this fireside chat offers valuable insights on ho...
Mar. 30, 2015 04:45 PM EDT Reads: 878
It's 2:15pm on a Friday, and I'm sitting in the keynote hall at PyCon 2013 fidgeting through a succession of lightning talks that have very little relevance to my life. Topics like "Python code coverage techniques" (ho-hum) and "Controlling Christmas lights with Python” (yawn - I wonder if there's anything new on Hacker News)...when Solomon Hykes takes the stage, unveils Docker, and the world shifts. If you haven't seen it yet, you should watch the video of Solomon's Pycon The Future of Linux C...
Mar. 30, 2015 04:15 PM EDT Reads: 374
SYS-CON Events announced today that Solgenia will exhibit at SYS-CON's 16th International Cloud Expo®, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY, and the 17th International Cloud Expo®, which will take place on November 3–5, 2015, at the Santa Clara Convention Center in Santa Clara, CA. Solgenia is the global market leader in Cloud Collaboration and Cloud Infrastructure software solutions. Designed to “Bridge the Gap” between Personal and Professional S...
Mar. 30, 2015 03:00 PM EDT Reads: 2,932
SYS-CON Events announced today that MangoApps will exhibit at SYS-CON's 16th International Cloud Expo®, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY., and the 17th International Cloud Expo®, which will take place on November 3–5, 2015, at the Santa Clara Convention Center in Santa Clara, CA. MangoApps provides private all-in-one social intranets allowing workers to securely collaborate from anywhere in the world and from any device. Social, mobile, and eas...
Mar. 30, 2015 03:00 PM EDT Reads: 3,134
You hear the terms “subscription economy” and “subscription commerce” all the time. And with good reason. Subscription-based monetization is transforming business as we know it. But what about usage? Where’s the “consumption economy”? Turns out, it’s all around us. When most people think of usage-based billing, the example that probably comes to mind first is metered public utilities — water, gas and electric. Phone services, especially mobile, might come next. Then maybe taxis. And that’s ab...
Mar. 30, 2015 02:45 PM EDT Reads: 750
Exelon Corporation employs technology and process improvements to optimize their IT operations, manage a merger and acquisition transition, and to bring outsourced IT operations back in-house. To learn more about how this leading energy provider in the US, with a family of companies having $23.5 billion in annual revenue, accomplishes these goals we're joined by Jason Thomas, Manager of Service, Asset and Release Management at Exelon. The discussion is moderated by me, Dana Gardner, Principal A...
Mar. 30, 2015 02:30 PM EDT Reads: 813
This month I want to revisit supporting infrastructure and datacenter environments. I have touched (some would say rant) upon this topic since my post in April 2014 called "Take a Holistic View of Support". My thoughts and views on this topic have not changed at all: it's critical for any organization to have a holistic, comprehensive strategy and view of how they support their IT infrastructure and datacenter environments. In fact, I believe it's even more critical today then it was a year ago ...
Mar. 30, 2015 02:00 PM EDT Reads: 690
As a group of concepts, DevOps has converged on several prominent themes including continuous software delivery, automation, and configuration management (CM). These integral pieces often form the pillars of an organization’s DevOps efforts, even as other bigger pieces like overarching best practices and guidelines are still being tried and tested. Being that DevOps is a relatively new paradigm - movement - methodology - [insert your own label here], standards around it have yet to be codified a...
Mar. 30, 2015 01:00 PM EDT Reads: 754
Modern Systems announced completion of a successful project with its new Rapid Program Modernization (eavRPMa"c) software. The eavRPMa"c technology architecturally transforms legacy applications, enabling faster feature development and reducing time-to-market for critical software updates. Working with Modern Systems, the University of California at Santa Barbara (UCSB) leveraged eavRPMa"c to transform its Student Information System from Software AG's Natural syntax to a modern application lev...
Mar. 30, 2015 01:00 PM EDT Reads: 1,068
When it comes to microservices there are myths and uncertainty about the journey ahead. Deploying a “Hello World” app on Docker is a long way from making microservices work in real enterprises with large applications, complex environments and existing organizational structures. February 19, 2015 10:00am PT / 1:00pm ET → 45 Minutes Join our four experts: Special host Gene Kim, Gary Gruver, Randy Shoup and XebiaLabs’ Andrew Phillips as they explore the realities of microservices in today’s IT worl...
Mar. 30, 2015 12:45 PM EDT Reads: 1,888
The world's leading Cloud event, Cloud Expo has launched Microservices Journal on the SYS-CON.com portal, featuring over 19,000 original articles, news stories, features, and blog entries. DevOps Journal is focused on this critical enterprise IT topic in the world of cloud computing. Microservices Journal offers top articles, news stories, and blog posts from the world's well-known experts and guarantees better exposure for its authors than any other publication. Follow new article posts on T...
Mar. 30, 2015 12:00 PM EDT Reads: 1,519
Hosted PaaS providers have given independent developers and startups huge advantages in efficiency and reduced time-to-market over their more process-bound counterparts in enterprises. Software frameworks are now available that allow enterprise IT departments to provide these same advantages for developers in their own organization. In his workshop session at DevOps Summit, Troy Topnik, ActiveState’s Technical Product Manager, will show how on-prem or cloud-hosted Private PaaS can enable organ...
Mar. 30, 2015 12:00 PM EDT Reads: 1,343
OmniTI has expanded its services to help customers automate their processes to deliver high quality applications to market faster. Consistent with its focus on IT agility and quality, OmniTI operates under DevOps principles, exploring the flow of value through the IT delivery process, identifying opportunities to eliminate waste, realign misaligned incentives, and open bottlenecks. OmniTI takes a unique, value-centric approach by plotting each opportunity in an effort-payoff quadrant, then work...
Mar. 30, 2015 11:15 AM EDT Reads: 1,008
For those of us that have been practicing SOA for over a decade, it's surprising that there's so much interest in microservices. In fairness microservices don't look like the vendor play that was early SOA in the early noughties. But experienced SOA practitioners everywhere will be wondering if microservices is actually a good thing. You see microservices is basically an SOA pattern that inherits all the well-known SOA principles and adds characteristics that address the use of SOA for distribut...
Mar. 30, 2015 11:00 AM EDT Reads: 1,091
Microservice architectures are the new hotness, even though they aren't really all that different (in principle) from the paradigm described by SOA (which is dead, or not dead, depending on whom you ask). One of the things this decompositional approach to application architecture does is encourage developers and operations (some might even say DevOps) to re-evaluate scaling strategies. In particular, the notion is forwarded that an application should be built to scale and then infrastructure sho...
Mar. 30, 2015 11:00 AM EDT Reads: 2,529
SYS-CON Events announced today the IoT Bootcamp – Jumpstart Your IoT Strategy, being held June 9–10, 2015, in conjunction with 16th Cloud Expo and Internet of @ThingsExpo at the Javits Center in New York City. This is your chance to jumpstart your IoT strategy. Combined with real-world scenarios and use cases, the IoT Bootcamp is not just based on presentations but includes hands-on demos and walkthroughs. We will introduce you to a variety of Do-It-Yourself IoT platforms including Arduino, Ras...
Mar. 30, 2015 11:00 AM EDT Reads: 2,154
Microservices are the result of decomposing applications. That may sound a lot like SOA, but SOA was based on an object-oriented (noun) premise; that is, services were built around an object - like a customer - with all the necessary operations (functions) that go along with it. SOA was also founded on a variety of standards (most of them coming out of OASIS) like SOAP, WSDL, XML and UDDI. Microservices have no standards (at least none deriving from a standards body or organization) and can be b...
Mar. 30, 2015 10:45 AM EDT Reads: 2,228
Our guest on the podcast this week is Jason Bloomberg, President at Intellyx. When we build services we want them to be lightweight, stateless and scalable while doing one thing really well. In today's cloud world, we're revisiting what to takes to make a good service in the first place. Listen in to learn why following "the book" doesn't necessarily mean that you're solving key business problems.
Mar. 30, 2015 10:45 AM EDT Reads: 1,333
Right off the bat, Newman advises that we should "think of microservices as a specific approach for SOA in the same way that XP or Scrum are specific approaches for Agile Software development". These analogies are very interesting because my expectation was that microservices is a pattern. So I might infer that microservices is a set of process techniques as opposed to an architectural approach. Yet in the book, Newman clearly includes some elements of concept model and architecture as well as p...
Mar. 30, 2015 10:15 AM EDT Reads: 2,173
Even though it’s now Microservices Journal, long-time fans of SOA World Magazine can take comfort in the fact that the URL – soa.sys-con.com – remains unchanged. And that’s no mistake, as microservices are really nothing more than a new and improved take on the Service-Oriented Architecture (SOA) best practices we struggled to hammer out over the last decade. Skeptics, however, might say that this change is nothing more than an exercise in buzzword-hopping. SOA is passé, and now that people are ...
Mar. 30, 2015 10:00 AM EDT Reads: 1,346