On Stateless Microservices

This post discusses the stateless microservice design pattern; it is meant as support material for other posts of mine that discuss microservices, mainly michael.gr - The Stateful Microservice.

Dory, the yellow-blue fish (a Royal Blue Tang) that suffered from amnesia in the 2003 movie Finding Nemo by Pixar.

Is statelessness a requirement for a microservice?

In another post of mine I discuss what a microservice really is, and I come to the conclusion that despite various attempts out there to define microservices using twenty-item-long lists of characteristics, a good working definition could be as simple as this: 

A microservice is a scalable and resilient module.

(See michael.gr - So, what is a Microservice, anyway?) 

Even if you disagree with the terseness of that definition, and you regard microservices as necessarily more than that, I hope you will at least agree that it is precisely scalability and resilience that the stateless microservice design pattern aims to address, so the definition serves its purpose at least in the context of this series of posts.

There are many who will try to convince you that in order to build a scalable and resilient system, you need statelessness; so much so, that microservices have almost come to be regarded as synonymous with statelessness. This post examines whether this is that in fact so, and what is the cost of doing things this way.

So, what is a Microservice, anyway?

This article attempts to shed some light on what a microservice really is; it is meant as support material for other posts of mine that discuss microservices, mainly michael.gr - The Stateful Microservice.

What is a microservice?

If you go looking for information out there, you will find many different descriptions of what a microservice is; these descriptions exhibit considerable difference of opinion, and to the extent that they agree, it is largely the result of copy-paste. One common theme in these descriptions is that in trying to define this elusive concept, they tend to assign fictitious properties to it. Often, the claims have nothing to do with what a microservice technically is, but rather with impertinent concepts such as the allegedly "independent" software development style around microservices, or some alleged organization of microservices "around business capabilities". Even when the claims do manage to stick within the technical realm, they range from the unwarranted to the preposterous. I have seen statements to the effect that a microservice is supposed to live in its very own source code repository, that a microservice must be independently deployable, that microservices must communicate with each other via REST, etc. (My favorite one is that they must necessarily be stateless; more on that in another post of mine; see  michael.gr - On Stateless Microservices.)

What is wrong with Scala

This is part of a series of posts in which I am documenting what is wrong with certain popular programming languages that I am (more or less) familiar with.  The aim of these posts is to support a future post in which I will be describing what the ideal programming language would look like for me.  

I will be amending and revising these texts over time.

What is wrong with C#

This is part of a series of posts in which I am documenting what is wrong with certain popular programming languages that I am (more or less) familiar with.  The aim of these posts is to support a future post in which I will be describing what the ideal programming language would look like for me.  

I will be amending and revising these texts over time.

What is wrong with Java

This is part of a series of posts in which I am documenting what is wrong with certain popular programming languages that I am (more or less) familiar with.  The aim of these posts is to support a future post in which I will be describing what the ideal programming language would look like for me.  

I will be amending and revising these texts over time.

What is wrong with C++

This is part of a series of posts in which I am documenting what is wrong with certain popular programming languages that I am (more or less) familiar with.  The aim of these posts is to support a future post in which I will be describing what the ideal programming language would look like for me.  

I will be amending and revising these texts over time.

[SOLVED] In Windows, how to recover an invisible application window

Scenario:

• You are using a laptop with one or more external monitors at home and (a different set of external monitors) at the office.

Problem:

• Every once in a while, when you switch between home and office, some buggy application will not handle its screen positioning correctly, so it will open up off-screen. In the taskbar you can see that the application has launched, but the application window is invisible.

How to fix:

Malicious Inaction

Actor Wayne Knight in the original Jurassic Park movie
playing the role of the unscrupulous programmer Dennis Nedry,
(anagram of "Nerdy",) the main villain.

Malicious Inaction (noun) any situation where a piece of software encounters an unexpected condition and responds by deliberately doing nothing, including not throwing an exception.  Synonyms: Silent Failure; Deliberate Malfunction; Unscrupulous Programming; Undermining; Sabotage; Treachery; Subversion; Vandalism.

I think that the term "Silent Failure" fails to express the amount of harm done.  Sure, the word "failure" indicates that something went wrong, but the word "silent" somewhat lessens the severity of the term, and it makes sound as if no feathers were ruffled, so it may have been alright.

Well, no. It was not alright. It never is. We need a stronger term to better capture the harm caused by the sinister practice of hiding error. We need a term that clearly conveys wrongdoing, a term that assigns blame and shame.

Hence, I present to the world my new and improved term: Malicious Inaction.

SVG in WPF

My notes on how to use SVG graphics in a WPF application

The Goal

The goal is to be able do do things like this:

    <Button Content="{StaticResource mySvgImage}">

... where mySvgImage somehow stands for a vector image that has somehow been obtained from an SVG file.  

The solution must not involve any proprietary, closed-source libraries.

Naturally, we want one of the following:

• either directly include SVG files into our application as resources, or, if that is not possible, then 
• have an "asset pipeline" approach where our SVG files are automatically converted during build into some format which is suitable for inclusion as a resource.

Java with Maven: Giving CI/CD a try

Please note that this is work in progress.  I am still working on it and refining it, as my understanding of it improves.

I have a set of public repositories on GitHub showcasing my work, (⬀) which is in java with maven. These projects are interdependent, so when you check out one of them, in order to compile and run it you need the binaries of some of the others. You could manually check out all of them and put them in an IDE project, but that's too much work. Solving this problem requires having Continuous Integration & Continuous Deployment (CI/CD) in place, so I decided to try my luck in setting one up using free services only.

The process involves three entities:

• A Source Repository.  (Where our source code is hosted.)
• I use GitHub for this.
• Possible alternatives:
• GitLab
• BitBucket
• A CI/CD provider. (Where the actual CI/CD takes place.)
• I decided to use CircleCI for this, but in retrospect it was a bad idea, because it does not support GitLab.
• Possible alternatives:
• GitLab - I want to use it as a source code repository, and I don't want to put all my eggs in one basket, so I don't want to use it for anything else.
• GitHub - I want to use it as a source code repository, and I don't want to put all my eggs in one basket, so I don't want to use it for anything else.
• BitBucket - it is by Atlassian. Need I say more.
• Appveyor - gives various errors like "There was an error while trying to complete the current operation. Please contact AppVeyor support." -- Lots of open source projects are using it though, so it might be worth a second try.
• Travis CI - only works with github.
• JFrog - overwhelmingly fancy front page followed by a not particularly fancy user experience once you get past the front page. Once I have registered, there is no way for me to log back in. 
• semaphoreci.com - only works with github.
• buddy.works - after you have given them your e-mail address, they tell you that it is free but they require a valid payment method.
• atlassian.com/software/bamboo - it is by Atlassian, need I say more.
• drone.io - not only it works with nothing other than github, they assume that I am using github, which is very annoying.
• octopus.com - registration fails with "Please use your work email address."
• buildkite.com - might work; not particularly user friendly.
• codefresh.io - might work; they unnecessarily complicate things with mandatory docker images.
• An Artifact Repository. (Where the binaries are stored.)
• I found a place called Repsy for this; Repsy is minimalistic, unrefined, and they even have bad English on their web site, but it will do for now.
• Possible alternatives:
• GitHub Packages
• GitLab Package Registry
• JFrog Artifactory

We begin with a situation where we already have the Source Repository (GitHub) and we want to set-up the CI/CD Provider (CircleCI) and the Artifact Repository (Repsy).