In this article written by Adam Boduch, author of the book JavaScript at Scale, goes on to say how we don't scale our software systems just because we can. While it's common to tout scalability, these claims need to be put into practice. In order to do so, there has to be a reason for scalable software. If there's no need to scale, then it's much easier, not to mention cost-effective, to simply build a system that doesn't scale. Putting something that was built to handle a wide variety of scaling issues into a context where scale isn't warranted just feels clunky. Especially to the end user.
So we, as JavaScript developers and architects, need to acknowledge and understand the influences that necessitate scalability. While it's true that not all JavaScript applications need to scale, it may not always be the case. For example, it's difficult to say that we know this system isn't going to need to scale in any meaningful way, so let's not invest the time and effort to make it scalable. Unless we're developing a throw-away system, there's always going to be expectations of growth and success.
At the opposite end of the spectrum, JavaScript applications aren't born as mature scalable systems. They grow up, accumulating scalable properties along the way. Scaling influencers are an effective tool for those of us working on JavaScript projects. We don't want to over-engineer something straight from inception, and we don't want to build something that's tied-down by early decisions, limiting its ability to scale.
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The need for scale
Scaling software is a reactive event. Thinking about scaling influencers helps us proactively prepare for these scaling events. In other systems, such as web application backends, these scaling events may be brief spikes, and are generally handled automatically. For example, there's an increased load due to more users issuing more requests. The load balancer kicks in and distributes the load evenly across backend servers. In the extreme case, the system may automatically provision new backend resources when needed, and destroy them when they're no longer of use.
Scaling events in the frontend aren't like that. Rather, the scaling events that take place generally happen over longer periods of time, and are more complex. The unique aspect of JavaScript applications is that the only hardware resources available to them are those available to the browser in which they run. They get their data from the backend, and this may scale up perfectly fine, but that's not what we're concerned with. As our software grows, a necessary side-effect of doing something successfully, is that we need to pay attention to the influencers of scale.
The preceding figure shows us a top-down flow chart of scaling influencers, starting with users, who require that our software implements features. Depending on various aspects of the features, such as their size and how they relate to other features, this influences the team of developers working on features. As we move down through the scaling influencers, this grows.
Growing user base
We're not building an application for just one user. If we were, there would be no need to scale our efforts. While what we build might be based on the requirements of one user representative, our software serves the needs of many users. We need to anticipate a growing user base as our application evolves. There's no exact target user count, although, depending on the nature of our application, we may set goals for the number of active users, possibly by benchmarking similar applications using a tool such as http://www.alexa.com/. For example, if our application is exposed on the public internet, we want lots of registered users. On the other hand, we might target private installations, and there, the number of users joining the system is a little slower. But even in the latter case, we still want the number of deployments to go up, increasing the total number of people using our software.
The number of users interacting with our frontend is the largest influencer of scale. With each user added, along with the various architectural perspectives, growth happens exponentially. If you look at it from a top-down point of view, users call the shots. At the end of the day, our application exists to serve them. The better we're able to scale our JavaScript code, the more users we'll please.
Building new features
Perhaps the most obvious side-effect of successful software with a strong user base is the features necessary to keep those users happy. The feature set grows along with the users of the system. This is often overlooked by projects, despite the obviousness of new features. We know they're coming, yet, little thought goes into how the endless stream of features going into our code impedes our ability to scale up our efforts.
This is especially tricky when the software is in its infancy. The organization developing the software will bend over backwards to reel in new users. And there's little consequence of doing so in the beginning because the side-effects are limited. There's not a lot of mature features, there's not a huge development team, and there's less chance of annoying existing users by breaking something that they've come to rely on. When these factors aren't there, it's easier for us to nimbly crank out the features and dazzle existing/prospective users. But how do we force ourselves to be mindful of these early design decisions? How do we make sure that we don't unnecessarily limit our ability to scale the software up, in terms of supporting more features?
New feature development, as well as enhancing existing features, is an ongoing issue with scalable JavaScript architecture. It's not just the number of features listed in the marketing literature of our software that we need to be concerned about . There's also the complexity of a given feature, how common our features are with one another, and how many moving parts each of these features has. If the user is the first level when looking at JavaScript architecture from a top-down perspective, each feature is the next level, and from there, it expands out into enormous complexity.
It's not just the individual users who make a given feature complex. Instead, it's a group of users that all need the same feature in order to use our software effectively. And from there, we have to start thinking about personas, or roles, and which features are available for which roles. The need for this type of organizational structure isn't made apparent till much later on in the game; after we've made decisions that make it difficult to introduce role-based feature delivery. And depending on how our software is deployed, we may have to support a variety of unique use cases. For example, if we have several large organizations as our customers, each with their own deployments, they'll likely have their own unique constraints on how users are structured. This is challenging, and our architecture needs to support the disparate needs of many organizations, if we're going to scale.
Hiring more developers
Making these features a reality requires solid JavaScript developers who know what they're doing, and if we're lucky, we'll be able to hire a team of them. The team part doesn't happen automatically. There's a level of trust and respect that needs to be established before the team members begin to actively rely on one another to crank out some awesome code. Once that starts happening, we're in good shape. Turning once again to the top-down perspective of our scaling influencers, the features we deliver can directly impact the health of our team. There's a balance that's essentially impossible to maintain, but we can at least get close. Too many features and not enough developers lead to a sense of perpetual inadequacy among team members. When there's no chance of delivering what's expected, there's not much sense in trying. On the other hand, if you have too many developers, and there's too much communication overhead due to a limited number of features, it's tough to define responsibilities. When there's no shared understanding of responsibilities, things start to break down.
It's actually easier to deal with not enough developers for the features we're trying to develop, than having too many developers. When there's a large burden of feature development, it's a good opportunity to step back and think—"what would we do differently if we had more developers?" This question usually gets skipped. We go hire more developers, and when they arrive, it's to everyone's surprise that there's no immediate improvement in feature throughput. This is why it's best to have an open development culture where there are no stupid questions, and where responsibilities are defined.
There's no one correct team structure or development methodology. The development team needs to apply itself to the issues faced by the software we're trying to deliver. The biggest hurdle is for sure the number, size, and complexity of features. So that's something we need to consider when forming our team initially, as well as when growing the team. This latter point is especially true because the team structure we used way back when the software was new isn't going to fit what we face when the features scale up.
Architectural perspectives
The preceding section was a sampling of the factors that influence scale in JavaScript applications. Starting from the top, each of these influencers affects the influencer below it. The number and nature of our users is the first and foremost influencer, and this has a direct impact on the number and nature of the features we develop. Further more, the size of the development team, and the structure of that team, are influenced by these features. Our job is to take these influencers of scale, and translate them into factors to consider from an architectural perspective:
Scaling influences the perspectives of our architecture. Our architecture, in turn, determines responses to scaling influencers. The process is iterative and never-ending throughout the lifetime of our software.
The browser is a unique environment
Scaling up in the traditional sense doesn't really work in a browser environment. When backend services are overwhelmed by demand, it's common to "throw more hardware" at the problem. Easier said than done of course, but it's a lot easier to scale up our data services these days, compared to 20 years ago. Today's software systems are designed with scalability in mind. It's helpful to our frontend application if the backend services are always available and always responsive, but that's just a small portion of the issues we face.
We can't throw more hardware at the web browsers running our code; given that; the time and space complexities of our algorithms are important. Desktop applications generally have a set of system requirements for running the software, such as OS version, minimum memory, minimum CPU, and so on. If we were to advertise requirements such as these in our JavaScript applications, our user base would shrink dramatically, and possibly generate some hate mail.
The expectation that browser-based web applications be lean and fast is an emergent phenomenon. Perhaps, that's due in part to the competition we face. There are a lot of bloated applications out there, and whether they're used in the browser or natively on the desktop, users know what bloat feels like, and generally run the other way:
JavaScript applications require many resources, all of different types; these are all fetched by the browser, on the application's behalf.
Adding to our trouble is the fact that we're using a platform that was designed as a means to download and display hypertext, to click on a link, and repeat. Now we're doing the same thing, except with full-sized applications. Multi-page applications are slowly being set aside in favor of single-page applications. That being said, the application is still treated as though it were a web page. Despite all that, we're in the midst of big changes. The browser is a fully viable web platform, the JavaScript language is maturing, and there are numerous W3C specifications in progress; they assist with treating our JavaScript more like an application and less like a document. Take a look at the following diagram:
A sampling of the technologies found in the growing web platform
We use architectural perspectives to assess any architectural design we come up with. It's a powerful technique to examine our design through a different lens. JavaScript architecture is no different, especially for those that scale. The difference between JavaScript architecture and architecture for other environments is that ours have unique perspectives. The browser environment requires that we think differently about how we design, build, and deploy applications. Anything that runs in the browser is transient by nature, and this changes software design practices that we've taken for granted over the years. Additionally, we spend more time coding our architectures than diagramming them. By the time we sketch anything out, it's been superseded by another specification or another tool.
Component design
At an architectural level, components are the main building blocks we work with. These may be very high-level components with several levels of abstraction. Or, they could be something exposed by a framework we're using, as many of these tools provide their own idea of "components".
When we first set out to build a JavaScript application with scale in mind, the composition of our components began to take shape. How our components are composed is a huge limiting factor in how we scale, because they set the standard. Components implement patterns for the sake of consistency, and it's important to get those patterns right:
Components have an internal structure. The complexity of this composition depends on the type of component under consideration
As we'll see, the design of our various components is closely-tied to the trade-offs we make in other perspectives. And that's a good thing, because it means that if we're paying attention to the scalable qualities we're after, we can go back and adjust the design of our components in order to meet those qualities.
Component communication
Components don't sit in the browser on their own. Components communicate with one another all the time. There's a wide variety of communication techniques at our disposal here. Component communication could be as simple as method invocation, or as complex as an asynchronous publish-subscribe event system. The approach we take with our architecture depends on our more specific goals. The challenge with components is that we often don't know what the ideal communication mechanism will be, till after we've started implementing our application. We have to make sure that we can adjust the chosen communication path:
The component communication mechanism decouples components, enabling scalable structures
Seldom will we implement our own communication mechanism for our components. Not when so many tools exist, that solve at least part of the problem for us. Most likely, we'll end up with a concoction of an existing tool for communication and our own implementation specifics. What's important is that the component communication mechanism is its own perspective, which can be designed independently of the components themselves.
Load time
JavaScript applications are always loading something. The biggest challenge is the application itself, loading all the static resources it needs to run, before the user is allowed to do anything. Then there's the application data. This needs to be loaded at some point, often on demand, and contributes to the overall latency experienced by the user. Load time is an important perspective, because it hugely contributes to the overall perception of our product quality.
The initial load is the user's first impression and this is where most components are initialized; it's tough to get the initial load to be fast without sacrificing performance in other areas
There's lots we can do here to offset the negative user experience of waiting for things to load. This includes utilizing web specifications that allow us to treat applications and the services they use as installable components in the web browser platform. Of course, these are all nascent ideas, but worth considering as they mature alongside our application.
Responsiveness
The second part of the performance perspective of our architecture is concerned with responsiveness. That is, after everything has loaded, how long does it take for us to respond to user input? Although this is a separate problem from that of loading resources from the backend, they're still closely-related. Often, user actions trigger API requests, and the techniques we employ to handle these workflows impact user-perceived responsiveness.
User-perceived responsiveness is affected by the time taken by our components to respond to DOM events; a lot can happen in between the initial DOM event and when we finally notify the user by updating the DOM.
Because of this necessary API interaction, user-perceived responsiveness is important. While we can't make the API go any faster, we can take steps to ensure that the user always has feedback from the UI and that feedback is immediate. Then, there's the responsiveness of simply navigating around the UI, using cached data that's already been loaded, for example. Every other architectural perspective is closely-tied to the performance of our JavaScript code, and ultimately, to the user-perceived responsiveness. This perspective is a subtle sanity-check for the design of our components and their chosen communication paths.
Addressability
Just because we're building a single-page application doesn't mean we no longer care about addressable URIs. This is perhaps the crowning achievement of the web— unique identifiers that point to the resource we want. We paste them in to our browser address bar and watch the magic happen. Our application most certainly has addressable resources, we just point to them differently. Instead of a URI that's parsed by the backend web server, where the page is constructed and sent back to the browser, it's our local JavaScript code that understands the URI:
Components listen to routers for route events and respond accordingly. A changing browser URI triggers these events.
Typically, these URIs will map to an API resource. When the user hits one of these URIs in our application, we'll translate the URI into another URI that's used to request backend data. The component we use to manage these application URIs is called a router, and there's lots of frameworks and libraries with a base implementation of a router. We'll likely use one of these.
The addressability perspective plays a major role in our architecture, because ensuring that the various aspects of our application have an addressable URI complicates our design. However, it can also make things easier if we're clever about it. We can have our components utilize the URIs in the same way a user utilizes links.
Configurability
Rarely does software do what you need it to straight out of the box. Highly-configurable software systems are touted as being good software systems. Configuration in the frontend is a challenge because there's several dimensions of configuration, not to mention the issue of where we store these configuration options. Default values for configurable components are problematic too—where do they come from? For example, is there a default language setting that's set until the user changes it? As is often the case, different deployments of our frontend will require different default values for these settings:
Component configuration values can come from the backend server, or from the web browser. Defaults must reside somewhere
Every configurable aspect of our software complicates its design. Not to mention the performance overhead and potential bugs. So, configurability is a large issue, and it's worth the time spent up-front discussing with various stakeholders what they value in terms of configurability. Depending on the nature of our deployment, users may value portability with their configuration. This means that their values need to be stored in the backend, under their account settings. Obviously decisions like these have backend design implications, and sometimes it's better to get away with approaches that don't require a modified backend service.
Making architectural trade-offs
There's a lot to consider from the various perspectives of our architecture, if we're going to build something that scales. We'll never get everything that we need out of every perspective simultaneously. This is why we make architectural trade-offs—we trade one aspect of our design for another more desirable aspect.
Defining your constants
Before we start making trade-offs, it's important to state explicitly what cannot be traded. What aspects of our design are so crucial to achieving scale that they must remain constant? For instance, a constant might be the number of entities rendered on a given page, or a maximum level of function call indirection. There shouldn't be a ton of these architectural constants, but they do exist. It's best if we keep them narrow in scope and limited in number. If we have too many strict design principles that cannot be violated or otherwise changed to fit our needs, we won't be able to easily adapt to changing influencers of scale.
Does it make sense to have constant design principles that never change, given the unpredictability of scaling influencers? It does, but only once they emerge and are obvious. So this may not be an up-front principle, though we'll often have at least one or two up-front principles to follow. The discovery of these principles may result from the early refactoring of code or the later success of our software. In any case, the constants we use going forward must be made explicit and be agreed upon by all those involved.
Performance for ease of development
Performance bottlenecks need to be fixed, or avoided in the first place where possible. Some performance bottlenecks are obvious and have an observable impact on the user experience. These need to be fixed immediately, because it means our code isn't scaling for some reason, and might even point to a larger design issue.
Other performance issues are relatively small. These are generally noticed by developers running benchmarks against code, trying by all means necessary to improve the performance. This doesn't scale well, because these smaller performance bottlenecks that aren't observable by the end user are time-consuming to fix. If our application is of a reasonable size, with more than a few developers working on it, we're not going to be able to keep up with feature development if everyone's fixing minor performance problems.
These micro-optimizations introduce specialized solutions into our code, and they're not exactly easy reading for other developers. On the other hand, if we let these minor inefficiencies go, we will manage to keep our code cleaner and thus easier to work with. Where possible, trade off optimized performance for better code quality. This improves our ability to scale from a number of perspectives.
Configurability for performance
It's nice to have generic components where nearly every aspect is configurable. However, this approach to component design comes at a performance cost. It's not noticeable at first, when there are few components, but as our software scales in feature count, the number of components grows, and so does the number of configuration options. Depending on the size of each component (its complexity, number of configuration options, and so forth) the potential for performance degradation increases exponentially. Take a look at the following diagram:
The component on the left has twice as many configuration options as the component on the right. It's also twice as difficult to use and maintain.
We can keep our configuration options around as long as there're no performance issues affecting our users. Just keep in mind that we may have to remove certain options in an effort to remove performance bottlenecks. It's unlikely that configurability is going to be our main source of performance issues. It's also easy to get carried away as we scale and add features. We'll find, retrospectively, that we created configuration options at design time that we thought would be helpful, but turned out to be nothing but overhead. Trade off configurability for performance when there's no tangible benefit to having the configuration option.
Performance for substitutability
A related problem to that of configurability is substitutability. Our user interface performs well, but as our user base grows and more features are added, we discover that certain components cannot be easily substituted with another. This can be a developmental problem, where we want to design a new component to replace something pre-existing. Or perhaps we need to substitute components at runtime.
Our ability to substitute components lies mostly with the component communication model. If the new component is able to send/receive messages/events the same as the existing component, then it's a fairly straightforward substitution. However, not all aspects of our software are substitutable. In the interest of performance, there may not even be a component to replace.
As we scale, we may need to re-factor larger components into smaller components that are replaceable. By doing so, we're introducing a new level of indirection, and a performance hit. Trade off minor performance penalties to gain substitutability that aids in other aspects of scaling our architecture.
Ease of development for addressability
Assigning addressable URIs to resources in our application certainly makes implementing features more difficult. Do we actually need URIs for every resource exposed by our application? Probably not. For the sake of consistency though, it would make sense to have URIs for almost every resource. If we don't have a router and URI generation scheme that's consistent and easy to follow, we're more likely to skip implementing URIs for certain resources.
It's almost always better to have the added burden of assigning URIs to every resource in our application than to skip out on URIs. Or worse still, not supporting addressable resources at all. URIs make our application behave like the rest of the Web; the training ground for all our users. For example, perhaps URI generation and routes are a constant for anything in our application—a trade-off that cannot happen. Trade off ease of development for addressability in almost every case. The ease of development problem with regard to URIs can be tackled in more depth as the software matures.
Maintainability for performance
The ease with which features are developed in our software boils down to the development team and it's scaling influencers. For example, we could face pressure to hire entry-level developers for budgetary reasons. How well this approach scales depends on our code. When we're concerned with performance, we're likely to introduce all kinds of intimidating code that relatively inexperienced developers will have trouble swallowing. Obviously, this impedes the ease of developing new features, and if it's difficult, it takes longer. This obviously does not scale with respect to customer demand.
Developers don't always have to struggle with understanding the unorthodox approaches we've taken to tackle performance bottlenecks in specific areas of the code. We can certainly help the situation by writing quality code that's understandable. Maybe even documentation. But we won't get all of this for free; if we're to support the team as a whole as it scales, we need to pay the productivity penalty in the short term for having to coach and mentor.
Trade off ease of development for performance in critical code paths that are heavily utilized and not modified often. We can't always escape the ugliness required for performance purposes, but if it's well-hidden, we'll gain the benefit of the more common code being comprehensible and self-explanatory. For example, low-level JavaScript libraries perform well and have a cohesive API that's easy to use. But if you look at some of the underlying code, it isn't pretty. That's our gain—having someone else maintain code that's ugly for performance reasons.
Our components on the left follow coding styles that are consistent and easy to read; they all utilize the high-performance library on the right, giving our application performance while isolating optimized code that's difficult to read and understand.
Less features for maintainability
When all else fails, we need to take a step back and look holistically at the featureset of our application. Can our architecture support them all? Is there a better alternative? Scrapping an architecture that we've sunk many hours into almost never makes sense—but it does happen. The majority of the time, however, we'll be asked to introduce a challenging set of features that violate one or more of our architectural constants.
When that happens, we're disrupting stable features that already exist, or we're introducing something of poor quality into the application. Neither case is good, and it's worth the time, the headache, and the cursing to work with the stakeholders to figure out what has to go.
If we've taken the time to figure out our architecture by making trade-offs, we should have a sound argument for why our software can't support hundreds of features.
When an architecture is full, we can't continue to scale. The key is understanding where that breaking threshold lies, so we can better understand and communicate it to stakeholders.
Leveraging frameworks
Frameworks exist to help us implement our architecture using a cohesive set of patterns. There's a lot of variety out there, and choosing which framework is a combination of personal taste, and fitness based on our design. For example, one JavaScript application framework will do a lot for us out-of-the-box, while another has even more features, but a lot of them we don't need.
JavaScript application frameworks vary in size and sophistication. Some come with batteries included, and some tend toward mechanism over policy. None of these frameworks were specifically designed for our application. Any purported ability of a framework needs to be taken with a grain of salt. The features advertised by frameworks are applied to a general case, and a simple one at that. Applied in the context of our architecture is something else entirely.
That being said, we can certainly use a given framework of our liking as input to the design process. If we really like the tool, and our team has experience using it, we can let it influence our design decisions. Just as long as we understand that the framework does not automatically respond to scaling influencers—that part is up to us.
It's worth the time investigating the framework to use for our project because choosing the wrong framework is a costly mistake. The realization that we should have gone with something else usually comes after we've implemented lots of functionality. The end result is lots of re-writing, re-planning, re-training, and re-documenting. Not to mention the time lost on the first implementation. Choose your frameworks wisely, and be cautious about being framework-coupling.
Summary
Scaling a JavaScript application isn't the same as scaling other types of applications. Although we can use JavaScript to create large-scale backend services, our concern is with scaling the applications our users interact with in the browser. And there're a number of influencers that guide our decision making process on producing an architecture that scales.
We reviewed some of these influencers, and how they flow in a top-down fashion, creating challenges unique to frontend JavaScript development. We examined the effect of more users, more features, and more developers; we can see that there's a lot to think about. While the browser is becoming a powerful platform, onto which we're delivering our applications, it still has constraints not found on other platforms.
Designing and implementing a scalable JavaScript application requires having an architecture. What the software must ultimately do is just one input to that design. The scaling influencers are key as well. From there, we address different perspectives of the architecture under consideration. Things such as component composition and responsiveness come into play when we talk about scale. These are observable aspects of our architecture that are impacted by influencers of scale.
As these scaling factors change over time, we use architectural perspectives as tools to modify our design, or the product to align with scaling challenges.
Resources for Article:
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