Posted by Jakub Holý on February 28, 2014
- Nathan Marz: Principles of Software Engineering, Part 1 - Nathan has worked with Big Data at Twitter and other places and really knows the perils or large, distributed, real-time systems and this post contains plenty of valuable advice for making robust, reliable SW. Main message: “there’s a lot of uncertainty in software engineering“; every SW operates correctly only for a certain range of inputs (including volume, HW it runs on, …) and you never control all of them so there always is an opportunity for failure; you can’t predict what inputs you will encounter in the wild. “[..] while software is deterministic, you can’t treat it as deterministic in any sort of practical sense if you want to build robust software.” “Making software robust is an iterative process: you build and test it as best you can, but inevitably in production you’ll discover new areas of the input space that lead to failure. Like rockets, it’s crucial to have excellent monitoring in place so that these issues can be diagnosed.“. From the content: Sources of uncertainty (bugs, humans, requirements, inputs, ..), Engineering for uncertainty (minimize dependencies, lessen % of cascading failure [JH: -> Hystrix], measure and monitor)
- Suffering-oriented programming is certainly also worth reading (summary: do not start with great designs; only start generalizing and creating libs when you have suffered enough from doing things more manually and thus learned the domain; make it possible > make it beautiful > make it fast, repeat)
- ThoughtWorks open-sources Go, continuous delivery platform - good bye, Jenkins! – better support for pipelines etc., see features and elementary concepts
- Cloud Design Patterns: Prescriptive Architecture Guidance for Cloud Applications (recommended by @markusbk so it must be good); Patterns: Cache-aside, Circuit Breaker, Compensating Transaction, Competing Consumers, Compute Resource Consolidation, Command and Query Responsibility Segregation (CQRS), Event Sourcing, External Configuration Store, Federated Identity, Gatekeeper, Health Endpoint Monitoring, Index Table, Leader Election, Materialized View, Pipes and Filters, Priority Queue, Queue-based Load Leveling, Retry, Runtime Reconfiguration, Scheduler Agent Supervisor, (data) Sharding, Static Content Hosting (-> CDN), Throttling, Valet Key.
Guidance topics: Asynchronous Messaging Primer, Autoscaling, Caching, Compute Partitioning, Data Consistency Primer, Data Partitioning, Data Replication and Synchronization, Instrumentation and Telemetry, Multiple Datacenter Deployment, Service Metering
- MOOC course Functional programming with Clojure at Uni of Helsinki – to get started you need, I suppose, follow the “Material and course content” – essentially read the text for each chapter, clone its repo, submit pull requests to get your work graded
- Jez Humble: The Case for Continuous Delivery - read to persuade manager about CD: “Still, many managers and executives remain unconvinced as to the benefits [of CD], and would like to know more about the economic drivers behind CD.” CD reduces waste: “[..]online controlled experiments (A/B tests) at Amazon. This approach created hundreds of millions of dollars of value[..],” reduces risks: “[..] Etsy, has a great presentation which describes how deploying more frequently improves the stability of web services.” CD makes development cheaper by reducing the cost of non-value-adding activities such as integration and testing. F.ex. HP got dev. costs down by 40%, dev cost/program by 78%
- Request Quest (via @jraregris) – entertaining and educational intractive quiz regarding what does (not) trigger a request in browsers and differences between them (and deviances from the standard) – img, script, css, etc.
- The REST Statelessness Constraint - a nice post about statelessness in REST if you, like me, don’t know REST so much in depth; highlights: Statelesness (and thus the requirement for clients to send their state with every request) is a trade-off crucial for web-scale and partially balanced by caching – while typical enterprise apps have different needs (more state, less scale) so REST isn’t a perfect match. Distinguish application (client-side) and server (resources) state. Using a DB to hold the state still violates the requirement. Use links to transfer some state (e.g. contain a link to fetch the next page of records in the response).
- CodeMesh 2013 presentations - good stuff! F.ex. Refactoring Functional Programs: Past and Future, Distribution, Scale and Flexibility with ZeroMQ, Deepak Giridharagopal on Puppet, Immutable Deployments, Analyzing Systems with PuppetDB, Francesco Cesarini and Viktor Klang on the Reactive Manifesto and more
- Cognitive Biases in Times of Uncertainty - people under pressure/stress start to focus on risks over gains and (very) short-term rather than long-term and thus also adopt 0-some mindset (i.e. if sb. else wins, I loose) => polarization into we x them and focus on getting as big piece of the cake possible at any price, now, dismissal of collaboration. With accelerating rate of change in the society due to technology, this is exactly what is happening. How to counter it? Create more positive narratives than the threat-based ones (views of the world), support them via short-term gains. Bottom line: each of us must work on spreading a more positive attitude to save us from bleak future.
- Book – Nathan Marz: Big Data - I dislike the big data hype (and, with passion, Hadoop) but would love to read this book; it presents a fresh look at big data processing, heavily inspired by functional programming. Nathan has plenty of experiences from Twitter and creating Storm and Cascalog (both in Clojure, btw.). Read ch 1: A new paradigm for big data.
- Facebook Engineering: The Mature Optimization Handbook (or go directly to the pdf, ePub, Mobi). If you get bored, jump directly to ch 5. Instrumentation.
Posted by Jakub Holý on November 30, 2013
Some interesting topics this time despite me spending lot of time on the Principles of Reactive Programming course: Java x Node.js, REST x other future-proof architectures, scary legacy code. Of course, also plenty of Clojure.
People, organizations, teams, development:
- Chris Argyris (1923-2013): An Appreciation – Thinkers 50 – recently departed Ch. Argyris is a person whose work you should know, if a bit interested in learning and organizations and how they (dis)function; and since we all work in organizations and want our work to be pleasant, this means all of us. We all want to work in orgs that do double-loop learning, i.e. they actually evovle as they learn. “Argyris argued that organizations depend fundamentally on people and that personal development is and can be related to work.” Now stop and go read it!
- Bob Marshall: The Antimatter Principle – “the only principle we need for becoming wildly effective at collaborative knowledge work” – can be summarized as “attend to folks’ needs” (importantly, including your own) => find out what people actually need, interpret their behavior (including anger, seemingly irrational or stupid requests etc.) in terms of needs; mastering this will make you excell in communication and effective work. Read the post to find out more.
- It’s a state of mind: some practical indicators on doing agile vs. being agile – are you agile or are just “doing agile”? Read on ti find out, if you dare! F.ex. “Non Agile teams have a process that slows the review of the changes.” Cocnlusion: “An Agile mindset is just that – a state of mind, a set of values. Its a constant questioning, and an opening up to possibilities. Its a predisposition to produce great things.“
- Johannes Brodwall: Humble architects – how to avoid being an architect that does more harm than good, as so many out there? Some tips: Don’t assume stupidity, Be aware that you might be wrong, Be careful with technology (i.e. simplicity beats everything; applies so much to us developers too!), Consistency isn’t as important as you think (or beware context), Tactical reuse in across systems is suboptimization (i.e. reuse has a cost), separate between (coding) rules and dogma (i.e. is that way unsafe, incomprehensible, or just a heresy w.r.t. a dogma?) Very valuable insights into creating good technical solutions and teams that work.
- Liz Keogh’s The Dream Team Nightmare: a Review – a very good review of this adventure-style book about coaching “agile” teams through (around?) common pitfalls, provides a good base for deciding whether you shall read the book (Liz essentially says yes)
- Fibonacci Kittens: One Idea One Commit – a short story of coming from biannual releases to frequent release of individual features; I link to this primarily to spread optimism, if this company managed it then, perhaps, we other can too?
- The Eternal Struggle Between Business and Programmers – “Business: More features! Now! Programmers: More refactoring! Now!” How can we resolve this eternal conflict of needs? This post reveals how the two parties can find a common ground and mutual understanding (beware, everybody must give up on something) and thus work together rather than against each other.
Coding, architecture, legacy
- Why the future is NOT RESTful – always refreshing to read something against the mainstream; “REST is not fit for the next generation of smart client applications because it has not been designed for smart clients.” According to the author, a smart client app stack needs: “1. persistence (storage and query), 2. documents/orm (conversion to tree-like datastructures), 3. data authorization (once authenticated), 4. pub/sub (websocket communications), 5. client db (client-side caching and querying), 6. templating (presentation level)” Meteor.js has nearly all but #3 thanks to mongodb (1+2), dpp (4), mongo on the client (5), spark (6). The author considers a similar but Clojure-based stack (with Datomic, Angular etc.) and looks at authorization possibilities. “Secured, personalised, CRUD operations are the future to a more simplified web.” We may agree or not but it certainly is worth reading.
- Michael Feathers (of Working Effectively With Legacy fame): Unconditional Programming – “Over and over again, I find that better code has fewer if-statements, fewer switches, and fewer loops. Often this happens because developers are using languages with better abstractions. [..] The problem with control structures is that they often make it easy to modify code in bad ways.” Includes a nice example of replacing if-else with much more readable and safer code.
- The Quality of Embedded Software, or the Mess Has Happened – an interesting and scary read about terrible spaghetti code (and hardware) that makes some Toyotas to accelerate when the driver tries to break; 11,000 global variables, the key function showing so high cyclomatix complexity that “makes it impossible not only to test but even maintain this program in any way.” Then 80k violations of the car industry coding standard cannot surprise. And a safety control that does not work. Interesting that a great manufacturer may have so terrible IT (and Toyota isn’t the only one).
- The string type is broken – the String type is M. Feathers’ favourite example of a leaky abstraction – most languages fail to process/split/count less common Unicode characters properly, the fact that String is implemented as a series of bytes leaks through (UTF-16 langs like Java); worth reading to be aware of the limitations
- Why I’m Productive In Clojure – some interesting points about simplicity, consciousness, interactive development, power without overwhelming fatures, etc. “With it [Clojure] I can always easily derive a solution to a particular problem from a small set of general patterns. [..] However, the number of ways that these concepts can be combined to solve all manner of problems appears to be inexhaustible.“
- Node.js at PayPal – PayPal is switching from Java to Node.js (among others to promote language consistency) and, as a part of that, has implemented the same app in Node and Java; results: Node was done earlier, had less code, performed better (though, as Daniel Kvasnička pointed out, “Comparing Node.js and servlet-based archs is not fair… compare Node with @vertx_project and you’ll get a whole different story ;)”; also, as Charles Nutter said, “The
@PayPal numbers for their Java to Node move are absurd. A JVM app doing 1.8 pages/s isn’t slow…it’s broken.“)
- IBM: Developing mobile apps with Node.js and MongoDB, Part 1: A team’s methods and results – also IBM has implemented the same (REST) app once with Java and DB2, once with Node and Mongo where Node+Mongo required less work and performed better; one of the great wins was having JSON as a native structure everywhere instead of transforming from/to it so Mongo is, in my opinion, an important factor in this particular case
- Dynamics of Programming: Benefits of Scala in CS1 – reasons for and experiences with using Scala in an introductory computer science course, worth reading; some of the advantages over Java are consistency (.asInt on String and Double vs. casting/parsing, no “primitive” types), REPL with time inference good for learning, functional style enables focus on what rather than how; quite persuasive arguments
- Stuart Sierra’s Component – a library for making it easier to implement Stuart’s reloadable workflow; a component is something that can be started, stopped, and depend on other components so that it is easier to do interactive REPL development
- Logan Linn: Clojure/conj 2013 – a pretty good overview of the conference
- Caribou – “the kernel of usefulness that has emerged from years of this basic practice“- a new Clojure web framework – seems to be interesting
- Results of the 2013 State of Clojure & ClojureScript survey and drill-down into what features people want – the most interesting fact is how many more participants use Clojure in production than last year and perhaps also the relatively wide adoption of Datomic among the respondents. Light Table has become the 3rd most popular dev. env., after Emacs and Vim. Some of the most mentioned language features requested were types (=> core.typed, Prismatic’s Schema), better error reporting (=> slingshot, dire, clj-stacktrace, io.aviso:pretty, etc.), debuger (though progress is being made)
- Book: Clojure High Performance Programming
- Improving Clojure Feedback : Stack Traces – making Clojure stacktraces more usable by filtering out noise and linking to relevant content – io.aviso:pretty, io.aviso:twixt
- Clojure Dev discussion: Hashing strategies – Executive summary – “In Clojure, however, it is far more common than in Java to use longs, vectors, sets, maps and compound objects comprised of those components (e.g., a map from vectors of longs to sets) as keys in other hash maps. It appears that Java’s hash strategy is not well-tuned for this kind of usage. Clojure’s hashing for longs, vectors, sets, and maps each suffer from some weaknesses that can multiply together to create a crippling number of collisions.” Ex.: An implementation of N-Queens took forever, spending most time on hash collisions. But be calm, smart Clojurians are working on a solution.
- Datomic Pro Starter Edition – Datomic with all storages, Datomic Console, a year of updates, full Datomic programming model; limitations: no HA transactor, no integrated memcached, max 2 peers and 1 transactor
- AirPair.com – a new site that enables developers to get help from other devs via remote pairing, code review, code mentoring etc. – a good opportunity to get help / help others (and earn something); I haven’t tried it but it sounds pretty interesting
MongoDB web stacks
- Meteor: JS frontend + MongoDB backend with changes in the DB pushed live to the clients, i.e. MongoDB is used both as the “application server” and storage. It seems great for apps where users need to collaborate in real-time with each other, certainly great for quick proof of concepts etc.; worth checking out; it also comes with free (at least for start?) hosting so really good for prototyping – “an open-source platform for building top-quality web apps in a fraction of the time.” The intro screencast will give you a good overview (10 min).
- Mean.io – MEAN (Mongo, Express, Angular, Node) stack Boilerplate – frontend, backend and storage using the same language and some of the most popular technologies (not that popular = best fit for you :)); it seems to be very new but since it just glues together 4 popular and documented technologies, that should not be an obstacle. There is an intro on the MongoDB blog.
[..] no organization should exist unless it is “of service” to its employees, its customers, its community.
- @Tom_Peters 28/11
I hope you’ll agree that there is a certain amount of irony involved in having to write repetitive code
- Dmitri Sotnikov in Why I’m Productive In Clojure
Happy teams are productive teams but:
Morale is 95% a function of the prevailing system (the way the work works). Which in turn is a function of the prevailing collective mindset
- @flowchainsensei Nov 10th
Posted in General, Languages, Top links of month | Tagged: agile, book, clojure, continuous_deployment, diy, legacy, mongodb, nodejs, SbE, scala, security | Comments Off
Posted by Jakub Holý on September 5, 2013
Use case: Deploy a new version of a webapp so that all new users are sent to the new
version while users with open sessions continue using the previous version
(so that they don’t loose their precious session state). Users of the new version
can explicitely ask for the previous version in the case that it doesn’t work as expected and vice versa.
Benefits: Get new features to users that need them as soon as possible without affecting
anybody negatively and without risking that a defect will prevent users from achieving their goal
(thanks to being able to fall back to the previous version).
Read the rest of this entry »
Posted in General | Tagged: continuous_deployment, DevOps, java | Comments Off
Posted by Jakub Holý on November 22, 2011
This post is inspired by Kent Beck’s excellent talk at JavaZone 2011 titled Software G Forces: The Effects of Acceleration where he describes how the development process, practices and partly the whole organization change and/or have to change as you go from annual to monthly to weekly, daily, hourly deployments. I’d like to summarize some of the points he made and use that as a ground for arguing that more frequent deployments are (in general) better.
I’d highly recommend you to watch his presentation as I will only reproduce parts of it (and as they are out of their original context, they might well not represent exactly what Kent wanted to communicate).
Kent argues that as you deploy more and more frequently, many things have to change including the business side of the software. What is a best practice for one of these speeds becomes an impediment for another one. With more frequent deployments teams have to progress towards the following practices, while leaving some other practices behind:
Read the rest of this entry »
Posted in General | Tagged: agile, continuous_deployment, development, DevOps, opinion | 2 Comments »
Posted by Jakub Holý on July 31, 2011
- Martin Fowler, M. Mason: Why not to use feature branches and prefer feature toggles instead, when branches can actually be used (video, 12min) – feature branches are pretty common yet they are a hindrance for a good and stable development pace due to “merging hells”. With trusted developers, feature toggles are a much better choice.
- M. Fowler: The LMAX Architecture – Martin describes the innovative and paradigm shaking architecture of the high-performance, high-volume financial trading platform LMAX. The platform can handle 6 million orders per second – using only a single java thread and commodity hardware. I highly recommend the article for two reasons: First, it crashes the common view that to handle such volumes you need multithreading. Second, for the rigorous, scientific approach used to arrive to this architecture. The key enablers are: 1) The main processing component does no blocking operations (I/O), those are done outside (in other threads). 2) There is no database – the state of the processor can be recreated by replaying the (persistent) input events. 3) To get further from 10k to 100k TPS they “just” wrote good code - well-factored, small methods (=> Hotspot more efficient, CPU can cache better). 4) To gain another multitude they implemented more efficient, cache-friendlier collections. All that was done based on evidence, enabled by thorough performance testing. 5) The processor and input/output components communicate without locking, using a shared (cyclic) array, where each of them operates on sum range of indexes and no element can ever be written by more than one component. Their internal range indexes do ever only increase so it is safe to read them without synchronization (at worst you will get old, lower value). The developers also tried Agents but found them in conflict with modern CPUs for their require context switch leading to emptying of the fast CPU caches.
Updated: Martin has published the post titled Memory Image which discusses the LMAX approach to persistence in a more general way.
- S. Mancuso: Working with legacy code with the goal of continual quality improvement – this was quite interesting for me as our team is in the same situation and arrived to quite similar approach. According to the author, the basic rule is “always first write tests for the piece code to be changed,” even though it takes so much time – he justifies it saying “when people think we are spending too much time to write a feature because we were writing tests for the existing code first, they are rarely considering the time spend elsewhere .. more time is created [lost] when bugs are found and the QA phase needs to be extended”. But it is also important to remember when to stop with refactoring to get also to creating business value and the rule for that is that quality improvements are done only with focus on a particular task. I like one of the concluding sentences: “Constantly increasing the quality level in a legacy system can make a massive difference in the amount of time and money spend on that project.”
- Uncle Bob: The Land that Scrum Forgot – Scrum makes it possible to be very productive at the beginning but to be able to keep the productivity and continue meeting the expectations that are thus created we need to concentrate on some essential technical practices and code quality. Because otherwise we create a mess of growing complexity – the ultimate killer of productivity. Uncle Bob advices us what practices and how to apply to attain both high, sustainable productivity and (as required for it) high code quality. It’s essential to realize that people do what they are incented to do and thus we must measure and reward both going fast and staying clean.
How do we measure quality? There is no perfect measure but we can build on the available established metrics – coverage, # (new) tests, # defects, size of tests (~ size of production code, 5-20 lines per method), test speed, cyclomatic complexity, function (< 20) and class (< 500) sizes, Brathwaite Correlation (> 2), dependency metrics (no cycles, in the direction abstraction).
The practices that enable us to stay clean include among others TDD, using tools like Chceckstyle, FindBugs to find problems and duplication, implementing Continuous Integration.
- Getting Started: Testing Concurrent Java Code – very good and worthy overview of tools for checking and testing of concurrent code with links to valuable resources. The author mentions among others FindBugs, concurrent test coverage (critical sections examined by multiple threads) measurement with IBM’s ConTest, multithreaded testing with ConTest (randomly tries to create thread interleaving situations; trial version – contact the authors for the full one) and MultithreadedTC (which divides time into “ticks” and enables you to fine-configure the interactions)
- The top 9+7 things every programmer or architect should know – quite good selection of nine, respectively 7 things from the famous (on-line available) books 97 Things every programmer/architect should know.
- Beans and noses – J. Spool reveals the First Rule of Consultancy: “No matter how much you try, you can’t stop people from sticking beans up their nose.” In other words, sometimes your clients decide to do some very unwise thing and no amount of reasoning can discourage them from that (quite understandably, as already the way they got to this decision defies logic). “The only thing I can do in a beans-and-noses situation is wait. Wait until the bean is in its final resting place.” Then you ask the person how it is working for him and “… if sticking a bean deep into their nostril doesn’t meet the very high expectations they’d had, I can now start talking alternative approaches to reaching those expectations.” Already before you can actually ask them about their expectations, in some cases (50:50) this discussion can lead them to realize they could achieve them with an alternative, less painful approach. Now, if you have read up to this point, you clearly have enough time, so go an read the article because it’s really orth it!
Posted in Languages, Testing, Tools, Top links of month | Tagged: architecture, continuous_deployment, java, Jenkins, legacy, quality, scrum | Comments Off