AKF Turns 10 – And It’s Still Not About the Tech
March 23, 2017 | Posted By: AKF
The caller ID was blocked but Marty had been expecting the call. Three “highly connected” people – donors, political advisers and “inner circle” people – had suggested AKF could help. It was October 2013 and Healthcare.gov had launched only to crash when users tried to sign up. President Obama appointed Jeffrey Zients to mop up the post launch mess. Once the crisis was over, the Government Accountability Office (GAO) released its postmortem citing inadequate capacity planning, software coding errors, and lack of functionality as root causes. AKF’s analysis was completely different – largely because we think differently than most technologists. While our findings indicated the bottlenecks that kept the site from scaling, we also identified failures in leadership and a dysfunctional organization structure. These latter, and more important, problems prevented the team from identifying and preventing recurring issues.
We haven’t always thought differently. Our early focus in 2007 was to help companies overcome architectural problems related to scale and availability. We’ve helped our clients solve some of the largest and challenging problems ever encountered – cyber Monday ecommerce purchasing, Christmas day gift card redemption, and April 15th tax filings. But shortly after starting our firm, we realized there was something common to our early engagements that created and sometimes turbocharged the technology failures. This realization, that people and processes – NOT TECHNOLOGY– are the causes of most failures led us to think differently. Too often we see technology leaders focusing too much on the technology and not enough on leading, growing, and scaling their teams.
We challenge the notion that technology leaders should be selected and promoted based on their technical acumen. We don’t accept that a technical leader should spend most of her time making the biggest technical decisions. We believe that technical executives, to be successful, must first be a business executive with great technical and business acumen. We teach teams how to analyze and successfully choose the appropriate architecture, organization, and processes to achieve a business outcome. Product effort is meaningless without a measurable and meaningful business outcome and we always put outcomes, not technical “religion” first.
If we can teach a team the “AKF way” the chance of project and business success increases dramatically. This may sound like marketing crap (did we mention we are also irreverent?), but our clients attest to it. This is what Terry Chabrowe, CEO eMarketer, said about us:
AKF served as our CTO for about 8 months and helped us make huge improvements in virtually every area related to IT and engineering. Just as important, they helped us identify the people on our team who could move into leadership positions. The entire AKF team was terrific. We’d never have been able to grow our user base tenfold without them.
A recent post claimed that 93% of successful companies abandon their original strategy. This is certainly true for AKF. Over the past 10 years we’ve massively changed our strategy of how we “help” companies. We’ve also quadrupled our team size, worked with over 350 companies, written three books, and most importantly made some great friendships. Whether you’ve read our books, engaged with our company, or connected with us on social media, thanks for an amazing 10 years. We look forward to the next 10 years, learning, teaching, and changing strategies with you.
Scalability Workshop in New York
April 19, 2017 | Posted By: AKF
AKF Scalability Workshop – New York
September 13 - 14, 2017
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Our workshop is designed for technology executives who are responsible for delivering highly available and highly scalable technical platforms & products. The principles we share can be applied to large organizations and start-ups alike. Our principles are technology-agnostic – we believe you can successfully scale with almost any technology if key concepts are followed. During our two-day workshop, you’ll participate in sessions that integrate our experience, research, and the work we’ve done with over 350 clients since 2007.
How is the workshop structured?
The workshop is delivered in 14 collaborative sessions over the 2-day event. While a member of the AKF team will lead the discussion in each session, much of the interaction comes from the participants themselves. We keep the session size limited (maximum of 25 attendees) so that each attendee can be an active part of the conversation, share experiences, and ask questions from other executives who have been in your shoes. You’ll leave the workshop with principles, tools, and examples that you can continuously apply to your platform and organization.
Who should attend the workshop?
Our event is designed for current CTOs, VPs of Engineering, Chief Architects, and other technology executives who want to improve their management, leadership, and technology skills. We help companies scale their technology and product platforms. Although nearly any technical organization would benefit from the lessons shared in the workshop, our sessions will provide the most value to companies that use technology to deliver their core product or service (e.g. SaaS, eCommerce).
What topics are covered in the workshop?
• The CTO Role: A discussion on the diversity of expectations and responsibilities from the 400 companies we have worked with at AKF Partners.
• The Right People & Roles: Ensuring the right talent is placed in positions for success.
• Management & Leadership: The skills of a transformational leader and highly effective manager.
• Conflict & Innovation: A discussion of good and bad conflicts in organizations and how to increase innovation.
• Multidisciplinary Agile Teams: Building innovative teams with diverse experience and skills.
• Team Goals & KPIs: Setting goals, metrics, and KPIs for Agile teams to ensure success.
• The Experiential Chasm: The widening gap between business leaders and technology leaders and how to close it.
• Service Delivery Mindset: The most successful technology organizations are structured with a service oriented mindset and we will discuss how to transform your organization and mindset.
• AKF Risk Model: Our viewpoint of risk and how to manage it successfully in your architecture, people, and processes.
• Highly Scalable Architectures: An in-depth look at creating highly scalable and available architectures
• AKF Scale Cube: Our approach to designing highly scalable architectures.
• Creating Fault Isolation: The importance of isolation for availability and time to market.
• Architecture Principles: An in-depth look at the top architecture principles and how to apply them.
• Processes for a Learning Organization: The most effective processes to put in place to create a successful learning organization.
Who will be teaching this workshop?
The workshop will be delivered by AKF Managing Partner, Marty Abbott, as well as AKF Partner Drew Morrell. Marty, along with Mike Fisher and Tom Keeven, helped found AKF Partners nine years ago with the goal of leveraging their successes (and failures!) as technology executives to help other companies prepare for and achieve hyper-growth. To date, AKF has helped over 350 companies across 18 countries make progress towards their scalability goals (including many leaders in the internet industry). Marty and Mike have co-authored three books: “The Art of Scalability”, “Scalability Rules”, and “The Power of Customer Misbehavior.”
When and where is the workshop?
The workshop is covered over two days: Wednesday, September 13th – Thursday, September 14th.
The workshop will take place here:
Bryant Park Hotel
40 West 40th Street
New York, NY 10018
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When Should You Split Services?
April 3, 2017 | Posted By: AKF
The Y axis of the AKF Scale Cube indicates that growing companies should consider splitting their products along services (verb) or resources (noun) oriented boundaries. A common question we receive is “how granular should one make a services split?” A similar question to this is “how many swim lanes should our application be split into?” To help answer these questions, we’ve put together a list of considerations based on developer throughput, availability, scalability, and cost. By considering these, you can decide if your application should be grouped into a large, monolithic codebases or split up into smaller individual services and swim lanes. You must also keep in mind that splitting too aggressively can be overly costly and have little return for the effort involved. Companies with little to no growth will be better served focusing their resources on developing a marketable product than by fine tuning their service sizes using the considerations below.
Frequency of Change – Services with a high rate of change in a monolithic codebase cause competition for code resources and can create a number of time to market impacting conflicts between teams including product merge conflicts. Such high change services should be split off into small granular services and ideally placed in their own fault isolative swim lane such that the frequent updates don’t impact other services. Services with low rates of change can be grouped together as there is little value created from disaggregation and a lower level of risk of being impacted by updates.
The diagram below illustrates the relationship we recommend between functionality, frequency of updates, and relative percentage of the codebase. Your high risk, business critical services should reside in the upper right portion being frequently updated by small, dedicated teams. The lower risk functions that rarely change can be grouped together into larger, monolithic services as shown in the bottom left.
Degree of Reuse – If libraries or services have a high level of reuse throughout the product, consider separating and maintaining them apart from code that is specialized for individual features or services. A service in this regard may be something that is linked at compile time, deployed as a shared dynamically loadable library or operate as an independent runtime service.
Team Size – Small, dedicated teams can handle micro services with limited functionality and high rates of change, or large functionality (monolithic solutions) with low rates of change. This will give them a better sense of ownership, increase specialization, and allow them to work autonomously. Team size also has an impact on whether a service should be split. The larger the team, the higher the coordination overhead inherent to the team and the greater the need to consider splitting the team to reduce codebase conflict. In this scenario, we are splitting the product up primarily based on reducing the size of the team in order to reduce product conflicts. Ideally splits would be made based on evaluating the availability increases they allow, the scalability they enable or how they decrease the time to market of development.
Specialized Skills – Some services may need special skills in development that are distinct from the remainder of the team. You may for instance have the need to have some portion of your product run very fast. They in turn may require a compiled language and a great depth of knowledge in algorithms and asymptotic analysis. These engineers may have a completely different skillset than the remainder of your code base which may in turn be interpreted and mostly focused on user interaction and experience. In other cases, you may have code that requires deep domain experience in a very specific area like payments. Each of these are examples of considerations that may indicate a need to split into a service and which may inform the size of that service.
Availability and Fault Tolerance Considerations:
Desired Reliability – If other functions can afford to be impacted when the service fails, then you may be fine grouping them together into a larger service. Indeed, sometimes certain functions should NOT work if another function fails (e.g. one should not be able to trade in an equity trading platform if the solution that understands how many equities are available to trade is not available). However, if you require each function to be available independent of the others, then split them into individual services.
Criticality to the Business – Determine how important the service is to business value creation while also taking into account the service’s visibility. One way to view this is to measure the cost of one hour of downtime against a day’s total revenue. If the business can’t afford for the service to fail, split it up until the impact is more acceptable.
Risk of Failure – Determine the different failure modes for the service (e.g. a billing service charging the wrong amount), what the likelihood and severity of each failure mode occurring is, and how likely you are to detect the failure should it happen. The higher the risk, the greater the segmentation should be.
Scalability of Data – A service may be already be a small percentage of the codebase, but as the data that the service needs to operate scales up, it may make sense to split again.
Scalability of Services – What is the volume of usage relative to the rest of the services? For example, one service may need to support short bursts during peak hours while another has steady, gradual growth. If you separate them, you can address their needs independently without having to over engineer a solution to satisfy both.
Dependency on Other Service’s Data – If the dependency on another service’s data can’t be removed or handled with an asynchronous call, the benefits of disaggregating the service probably won’t outweigh the effort required to make the split.
Effort to Split the Code – If the services are so tightly bound that it will take months to split them, you’ll have to decide whether the value created is worth the time spent. You’ll also need to take into account the effort required to develop the deployment scripts for the new service.
Shared Persistent Storage Tier – If you split off the new service, but it still relies on a shared database, you may not fully realize the benefits of disaggregation. Placing a readonly DB replica in the new service’s swim lane will increase performance and availability, but it can also raise the effort and cost required.
Network Configuration – Does the service need its own subdomain? Will you need to make changes load balancer routing or firewall rules? Depending on the team’s expertise, some network changes require more effort than others. Ensure you consider these changes in the total cost of the split.
The illustration below can be used to quickly determine whether a service or function should be segmented into smaller microservices, be grouped together with similar or dependent services, or remain in a multifunctional, infrequently changing monolith.
April 3, 2017 | Posted By: AKF
A topic that often results in great debate is “how to measure engineers?” I’m a pretty data driven guy so I’m a fan of metrics as long as they are 1) measured correctly 2) used properly and 3) not taken in isolation. I’ll touch on these issues with metrics later in the post, let’s first discuss a few possible metrics that you might consider using. Three of my favorite are: velocity, efficiency, and cost.
- Velocity – This is a measurement that comes from the Agile development methodology. Velocity is the aggregate of story
points (or any other unit of estimate that you use e.g. ideal days) that engineers on a team complete in a sprint. As we will
discuss later, there is no standard good or bad for this metric and it is not intended to be used to compare one engineer to
another. This metric should be used to help the engineer get better at estimating, that’s it. No pushing for more story points
or comparing one team to another, just use it as feedback to the engineers and team so they can get more predictable in
- Efficiency – The amount of time a software developer spends doing development related activities (e.g. coding, designing,
discussing with the product manager, etc) divided by their total time available (assume 8 – 10 hours per day) provides the
Engineering Efficiency. This is a metric designed to see how much time software developers are actually spending on
developing software. This metric often surprises people. Achieving 60% or more is exceptional. We often see dev groups
below 40% efficiency. This metric is useful for identifying where else engineers are spending their time. Are there too many
company meetings not directly related to getting products out the door? Are you doing too many HR training sessions, etc?
This metric is really for the management team to then identify what is eating up the nondevelopment
time and get rid of it.
- Cost – Tech cost as a percentage of revenue is a good cost based metric to see how much you are spending on technology.
This is very useful as it can be compared to other tech (SaaS or other webbased companies) and you can watch this metric change over time. Most startups begin with their total tech cost (engineers, hosting, etc) at well over 50% of revenue but this should quickly reduce as revenue grows and the business scales. Yes, scaling a business involves growing it cost effectively. Established companies with revenues in the tens of millions range usually have this percentage below 10%. Very large companies in the hundreds of millions in revenue often drive this down to 57%.
Now that we know about some of the most common metrics, how should they be used? The most common way managers and executives want to use metrics is to compare engineers to each other or compare a team over time. This works for the Efficiency and the Cost metrics, which by the way are primarily measurements of management effectiveness. Managers make most of the cost decisions including staffing, vendor contracts, etc. so they should be on the hook to improve these metrics. In terms of product out the door as measured by story points completed each sprint a.k.a. Velocity, as mentioned above, is to be used to improve estimates, not try to speed up developers. Using this metric incorrectly will just result in bloated estimates, not faster development.
An interesting comparison of developers comes from a 1967 article by Grant and Sackman in which they stated a ratio of 28:1 for the time required by the slowest versus the fastest programmer to complete a task. This has been a widely cited ratio but a paper from 2000 revised this number to 4:1 at the most and more likely 2:1. While a 2x difference in speed is still impressive it doesn’t optimize for the overall quality of the product. An engineer who is very fast and with high quality but doesn’t interact with the product managers isn’t necessarily the overall most effective. My point is that there are many other factors to be considered than just story points per release when comparing engineers.
Splitting Databases for Scale
April 3, 2017 | Posted By: AKF
The most common point of congestion and therefore barrier to scale that we see in our practice is the database. Referring back to our earlier article “Splitting Applications or Services for Scale”, it is very common for engineers to create scalability along the X axis of our cube by persisting data in a single monolithic database and having multiple “cloned” applications servers retrieve and store data within that database. For young companies this is a very good approach as if done properly it will also eliminate the need for persistence or affinity to a given application server and as a result will increase customer perceived availability.
The problem, however, with this single monolithic data structure is threefold:
- Even with clustering technology (the existence of a second physical system or database that can take the load of the first in the event of failure), failures of the primary database will result in short service outages for 100% of the user community.
- This approach ultimately relies solely on technical improvements in cpu speed, memory access speed, memory access size, mass
storage access speeds and size, etc to insure the companies needs for scale.
- Relying upon (2) above in the extreme cases is not the most cost effective solutions as the newest and fastest technologies come at
a premium to older generations of technology and do not necessarily have the same processing power per dollar as older and/or
smaller (fewer cpus etc) systems.
As we have argued in the aforementioned post, a great engineering team will think about how to scale their platform well in advance of the need to rely solely upon partner technology advances. By making small modifications to our previously presented “Scale Cube”, the same concepts applied to the problem of splitting services for scale can be useful in addressing how to split a database for scale. As with the AKF Services Scale Cube, the AKF Database Scale Cube consists of an X, Y and Z axes – each addressing a different approach to scale transactions applied to a database. The lowest left point of the cube (coordinates X=0, Y=0 and Z=0) represents the worst case monolithic database – a case where all data is located in a single location and all accesses go to this single database.
The X Axis of the cube represents a means of spreading load across multiple instances of a replicated representation of the data. This is the first approach most companies use in scaling databases and is often both the easiest to implement and the least costly in both engineering time and hardware. Many third party and open source databases have native properties or functions that will allow the near real time replication of data to multiple “read databases”. The engineering cost of such an approach is low as typically database calls only need to be identified as a “read” or “write” and sent to the appropriate write database or bank of read databases. The “bank” of read databases should have reads evenly split across this if possible and many companies employ simple 3d party load balancers to perform this distribution.
Included in our Xaxis split are third party and open source caching solutions that allow reads to be split across “cache” hosts before actually reading from a database upon a cache miss. Caching is another simple way to reduce the load on the database but in our experience is not sufficient for hyper growth SaaS sites. If implemented properly, this Xaxis split also can increase availability as if replication is near real time, a read server can be promoted as the singular “write server” in the event of a “write server” failure. The combination of caching and read/write splits (our X axis) is sufficient for many companies but for companies with extreme hyper growth and massive data retention needs it is often not enough.
The Y Axis of our database cube represents a split by function, service or resource just as it did with the service cube. A service might represent a set of usecases and is most often easiest to envision through thinking of it as a verb or action like “login” and a resource oriented split is easiest to envision by thinking of splits as nouns like “account information”. These splits help handle not only the split of transactions across multiple systems as did the X axis, but can also be helpful in speeding up database calls by allowing more information specific to the request to be held in memory rather than needing to make a disk access. Just as with our approach in scaling services, our recommended approach to identify the order in which these splits should be accomplished is to determine which ones will give you the greatest “headroom” or capacity “runway” for the least amount of work. These splits often come at a higher cost to the engineering team as very often they will require that the application be split up as well. It is possible to take a monolithic application and perform physical splits by say URL/URI to different service or resource oriented pools. While this approach will help spread transaction processing across multiple systems similar to our X axis implementation it may not offer the added benefit of reducing the amount of system memory required by service / pool / resource / application. Another reason to consider this type of split in very large teams is to dedicate separate engineering teams to focus on specific services or resources in order to reduce your application learning curve, increase quality, decrease time to market (smaller code bases), etc. This type of split is often referred to as “swimlaning” an application and data set, especially when both the database and applications are split to represent a “failure domain” or fault isolative infrastructure.
The Z Axis represents ways to split transactions by performing a lookup, a modulus or other indiscriminate function (hash for instance). The most common way to view this is to consider splitting your resources by customer if your entity relationships allow that to happen. In the world of media, you might consider splitting it by article_id or media_id and in the world of commerce a split by product_id might be appropriate. In the case where you split customers from your products and perform splits within customers and products you would be implementing both a Y axis split (splitting by resource or call – customers and products) and a Z axis split (a
modulus of customers and products within their functional splits).
Z axis splits tend to be the most costly for an engineering team to perform as often many functions that might be performed within the database (joins for instance) now need to be performed within the application. That said, if done appropriately they represent the greatest potential for scale for most companies.
Splitting Applications or Services for Scale
April 3, 2017 | Posted By: AKF
Splitting Applications or Services for Scale
Most internet enabled products start their life as a single application running on an appserver or appserver/webserver combination and potentially communicating with a database. Many if not all of the functions are likely to exist within a monolithic application code base making use of the same physical and virtual resources of the system upon which the functions operate: memory, cpu, disk, network interfaces, etc. Potentially the engineers have the forethought to make the system highly available by positioning a second application server in the mix to be used in the event that the first application server fails.
This monolithic design will likely work fine for many sites that receive low levels of traffic. However, if the product is very successful and receives wide and fast adoption user perceived response times are likely to significantly degrade to the point that the product is almost entirely unusable. At some point, the system will likely even fail under the load as the inbound request rate is significantly greater than the processing power of the system and the resulting departure rate of responses to requests.
A great engineering team will think about how to scale their platform well in advance of such a catastrophic failure. There are many ways to approach how to think about such scalability of a platform and we present several through a representation of a three dimensional cube addressing three approaches to scale that we call the AKF Scale Cube.
The AKF Scale Cube consists of an X, Y and Z axes – each addressing a different approach to scale a service. The lowest left point of the cube (coordinates X=0, Y=0 and Z=0) represents the worst case monolithic service or product identified above: a product wherein all functions exist within a single code base on a single server making use of that server’s finite resources of memory, cpu speed, network ports, mass storage, etc.
The X Axis of the cube represents a means of spreading load across multiple instances of the same application and data set. This is the first approach most companies use to scale their services and it is effective in scaling from a request per second perspective. Oftentimes it is sufficient to handle the scale needs of a moderate sized business. The engineering cost of such an approach is low compared to many of the other options as no significant rearchitecting of the code base is required unless the engineering team needs to eliminate affinity to a specific server because the application maintains state. The approach is simple: clone the system and service and allow it to exist on N servers with each server handling 1/Nth the total requests. Ideally the method of distribution is a loadbalancer configured in a highly available manner with a passive peer that becomes active should the active peer fail as a result of hardware or software problems. We do not recommend leveraging roundrobin DNS as a method of load balancing. If the application does maintain state there are various ways of solving this including a centralized state service, redesigning for statelessness, or as a last resort using the load balancer to provide persistent connections. While the Xaxis approach is sufficient for many companies and distributes the processing of requests across several hosts it does not address other potential bottlenecks like memory constraints where memory is used to cache information or results.
The Y Axis of the cube represents a split by function, service or resource. A service might represent a set of usecases and is most often easiest to envision through thinking of it as a verb or action like “login” and a resource oriented split is easiest to envision by thinking of splits as nouns like “account information”. These splits help handle not only the split of transactions across multiple systems as did the X axis, but can also be helpful in reducing or distributing the amount of memory dedicated to any given application across several systems. A recommended approach to identify the order in which these splits should be accomplished is to determine which ones will give you the greatest “headroom” or capacity “runway” for the least amount of work. These splits often come at a higher cost to the engineering team as very often they will require that the application be split up as well. As a quick first step, a monolithic application can be placed on multiple servers and dedicate certain of those servers to specific “services” or URIs. While this approach will help spread transaction processing across multiple systems similar to our X axis implementation it may not offer the added benefit of reducing the amount of system memory required by service/pool/resource/application. Another reason to consider this type of split in very large teams is to dedicate separate engineering teams to focus on specific services or resources in order to reduce your application learning curve, increase quality, decrease time to market (smaller code bases), etc. This type of split is often referred to as
“swimlaning” an application.
The Z Axis represents ways to split transactions by performing a lookup, a modulus or other indiscriminate function (hash for instance). As with the Y axis split, this split aids not only fault isolation, but significantly reduces the amount of memory necessary
(caching, etc) for most transactions and also reduces the amount of stabile storage to which the device/service needs attach. In this case, you might try a modulus by content id (article), or listing id, or a hash from the received IP address, etc. The Z axis split is often the most costly of all splits and we only recommend it for clients that have hypergrowth or very high rates of transaction. It should only be used after a company has implemented a very granular split along the Y axis. That said, it also can offer the greatest degree of scalability as the number of “swimlanes within swimlanes” that it creates is virtually limitless. For instance, if a company implements a Z axis split as a modulus of some transaction id and the implementation is a configurable number “N”, then N can be 10, 100, 1000, etc and each order of magnitude increase in N creates nearly an order of magnitude of greater scale for the company.
Scalability Best Practices
April 3, 2017 | Posted By: AKF
Here are a baker’s dozen of items that we feel are Best Practices for Scalability:
Use asynchronous communication when possible. Synchronous calls tie the availability of the two services together. If one has a failure or is slow the other one is affected.
2. Swim Lanes
Create fault isolated “swim lanes” of hardware by customer segmentation. This prevents problems with one customer from causing issues across all customers. This also helps with diagnosis of issues and code roll outs.
Make use of cache at multiple layers including object caches in front of databases (such as memcached), page or item caches for content (such as squid) and edge caches (such as Akamai).
Understand your application’s performance from a customer’s perspective. Monitor outside of your network and have tests that simulate a real user’s experience. Also monitor the internal working of the application in terms of query and transaction execution count and timing.
Replicate databases for recovery as well as to off load reads to multiple instances.
Split the application and databases by service and / or by customer using a modulus. While this requires slightly more complicated logic in the application it allows for massive scaling.
7. Use Few RDBMS Features
Use the OLTP database as a persistent storage device as much as possible. The more you rely on the features offered in most RDBMS for your transactions, the greater load you are putting on the hardest item in your system to scale. Remove all business logic from the database such as stored procedures and move it into the application. When significant scaling is required join in the application and not through the SQL.
8. Slow Roll
Roll out new code versions slowly, to a small subset of your servers without bringing the entire site down. This requires that all code be backwards compatible because you will have two versions of code running in production during the roll out. This method allows you to find problems that your quality and L&P testing missed while having minimal impact on customers.
9. Load & Performance Testing
Test the performance of the application version before it goes into production. This will not catch all the issues, which is why you need the ability to rollback, but it is very worthwhile.
10. Capacity Planning / Scalability Summits
Know how much capacity you have on all tiers and services in your system. Use Scalability Summits to plan for the increased capacity demands.
Always have the ability to rollback a code release.
12. Root Cause Analysis
Ensure you have a learning culture that is evident by utilizing Root Cause Analysis to find and fix the real cause of issues.
13. Quality From The Beginning
Quality can’t be tested into a product, it must be designed in from the beginning.
PDLC or SDLC
April 3, 2017 | Posted By: AKF
As a frequent technology writer I often find myself referring to the method or process that teams use to produce software. The two terms that are usually given for this are software development life cycle (SDLC) and product development life cycle (PDLC). The question that I have is are these really interchangeable? I don’t think so and here’s why.
Wikipedia, our collective intelligence, doesn’t have an entry for PDLC, but explains that the product life cycle has to do with the life of a product in the market and involves many professional disciplines. According to this definition the stages include market introduction, growth, mature, and saturation. This really isn’t the PDLC that I’m interested in. Under new product development (NDP) we find a defintion more akin to PDLC that includes the complete process of bringing a new product to market and includes the following steps: idea generation, idea screening, concept development, business analysis, beta testing, technical implementation, commercialization, and pricing.
Under SDLC, Wikipedia doesn’t let us down and explains it as a structure imposed on the development of software products. In the article are references to multiple different models including the classic waterfall as well as agile, RAD, and Scrum and others.
In my mind the PDLC is the overarching process of product development that includes the business units. The SDLC is the specific steps within the PDLC that are completed by the technical organization (product managers included). An image on HBSC’s site that doesn’t seem to have any accompanying explanation depicts this very well graphically.
Another way to explain the way I think of them is to me all professional software projects are products but not all product development includes software development. See the Venn diagram below. The upfront (bus analysis, competitive analysis, etc) and back end work (infrastructure, support, depreciation, etc) are part of the PDLC and are essential to get the software project created in the SDLC out the door successfully. There are non-software related products that still require a PDLC to develop.
Do you use them interchangeably? What do you think the differences are?
How to Scale a Read Subsystem
April 3, 2017 | Posted By: AKF
Many SaaS systems have a large part of the system dedicated to reading or searching for information. This read or search may be implemented in an ecommerce site as a product/inventory search based on keywords, or in a content site it may be a implemented as an unstructured string search or regular expression search against all indexed content.
In high transaction sites, this activity can be extremely taxing and even cost prohibitive on the primary database should be considered a great target for disaggregation along the Y axis of our scale cube as we describe in our database scaling post.
The AKF scale cube can be applied to read/search subsystems to create multiple dimensions of splits that will allow for near infinite scale. Below is our cube diagram depicting the three dimensions for scaling a read or search subsystem.
As with our past cubes, the X axis is the balancing of transaction load against multiple clones. This allows the system to scale in terms of transactions but not necessarily the size of data.
The Y axis is a split along function or service. While the read/search subsystem split is a Y axis split of the original database, we can recursively split this by creating read subsystems specific to a product catalog, userspecific information, order history, archived content, current content, recommended content, and on and on.
The Z axis is our modulus, lookup function or indiscriminate function split.
Let’s look at the X and Z axis to describe a physical system that can be easily scaled for reads. This physical architecture would be comprised of aggregators, load balancers, and an NxM matrix where N systems hold 1/Nth of the data and M storage systems each get 1/Mth of your transactions along those N dimensions. The storage subsystems don’t have to be relational databases, they could be in memory data stores such as memcached or Berkeley DB instances.
Read or search requests are load balanced to one of X (X scales with the number of requests being made) aggregators, each of which subsequently make N requests of the N unique data sets through a load balancer to one of M systems within the N data tiers. The Nunique responses are aggregated and sorted and returned to the customers.
click to enlarge
The benefit of such a system is that you can scale N easily with the number of items listed and M with the number of transactions requested. If N is sized appropriately, the items can all be returned from memory thereby further increasing transaction speed.
If you want higher speed and even greater fault tolerance, you can further split these read subsystems along the Y axis as described previously in this document.
Fault Isolative Architectures or “Swimlaning”
April 3, 2017 | Posted By: AKF
Two of our previous articles, Splitting Databases for Scale and Splitting Applications or Services for Scale have made references to a concept that we call “Swimlaning Architectures”.
The basics of this concept are covered in our two previous posts, but we have not spent a lot of time discussing the reasons for such a split or approach in technology architecture.
In our definition, a “Swimlane” is a failure domain. A failure domain is a group of services within a boundary such that any failure within that boundary is contained within the boundary and the failure does not propagate or affect services outside of said boundary. The benefit of such a failure domain is twofold:
1) Fault Detection: Given a granular enough approach, the component of availability associated with the time to identify the failure is significantly reduced. This is because all effort to find the root cause or failed component is isolated to the section of the product or platform associated with the failure domain.
2) Fault Isolation: As stated previously, the failure does not propagate or cause a deterioration of other services within the platform. As such, and depending upon approach only a portion of users or a portion of functionality of the product is affected.
A “swimlaned” architecture is one in which each failure domain is completely isolated. In order to achieve this, ideally there are no calls between swimlanes or failure domains. Synchronous calls are absolutely forbidden in this type of architecture as any synchronous call between failure domains, even with appropriate timeout and detection mechanisms is very likely to cause a series of failures across other domains. Strictly speaking, you do not have a failure domain if that domain is connected via a call to any other service in another domain, to any service outside of the domain, or if the domain receives calls from other domains or services.
It is acceptable, but not advisable, to have asynchronous calls between domains. If such a communication is necessary it is very important to include failure detection and timeouts even with the asynchronous calls to ensure that retries do not call port overloads on any services. Here is an interesting blog post about runaway scripts and their impact on Apache, PHP, and MySQL.
As we have previously indicated, a swimlane should have all of its services located within the failure domain. For instance, if database accesses are necessary the database with all appropriate information for that swimlane should exist within the same failure domain as all of the application and webservers necessary to perform the function or functions of the swimlane. Furthermore, that database should not be used for other requests of service from other swimlanes. Our rule is one production database on one host.
As we have indicated with our Scale Cube in the past, there are many ways in which to think about swimlaned architectures. You can think about them in terms of a separation of services e.g. “login” and “shopping cart” (two separate swimlanes) each having the web and app servers as well as all data stores located within the swimlane and answering only to systems within that swimlane. Corresponding to the Scale Cube we have previously introduced this would be a “Y” axis swimlane.
Another approach would be to perform a separation of your customer base or a separation of your order numbers or product catalog.
Assuming an indiscriminate function to perform this separation (like a modulus of id), such a split would be a Z axis swimlane along customer, order number or product id lines.
Combining the concepts of service and database separation into several fault isolative failure domains creates both a scalable and highly available platform.
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