A concept I’ve been trying to put a name to is software application architectures that inherently lend themselves to a lower rate of technical debt accumulation than others. This post is my first attempt to do that.

Technical Debt

Technical debt is a term that is used frequently in our industry and while its meaning is commonly understood among experienced technologists, it’s not clearly defined.

In the abstract:

• Technical debt is cost incurred from software design and implementation choices made in the past;
• Interest on that technical debt accrues and compounds as a result of subsequent decisions that are layered onto the original set of choices; and
• The full cost of technical debt is not known until, at some point in the future, there is a need to modify the software system which forces the development team to modify the original choices built into the existing system and calculate the level of effort needed to change them safely.

On this blog before we’ve covered a high level introduction to Akka.Streams for Akka.NET, but in this post we go into some more detail on:

1. What is Akka.Streams;
2. The motivations for using Akka.Streams; and
3. When should you use Akka.Streams?

In the recent past we blogged about hosting headless Akka.NET services using IHostedService and we thought we’d extend that train of thought to cover ASP.NET Core. .NET’s web ecosystem has changed a lot since 2015, when we last wrote about hosting Akka.NET with ASP.NET MVC and even NancyFX on .NET Framework 4.5 - so we’re due for an update.

So, we went ahead and put together a video: “Best Practices for Integrating Akka.NET and ASP.NET Core” which demonstrates how to work with Akka.NET and ASP.NET Core inside a single process.

This blog post accompanies that video and expands on some of the advice we give in it!

NOTE: Also, please check out our Petabridge.App.Web dotnet new template to use these patterns straight away inside your own applications!

Vertech is an industrial automation and information solutions company based out of the United States that develops solutions for a broad range of industries.

This case study was authored by John Wolnisty, a Solutions Architect at Vertech who, in the context of this case study, used Akka.NET to help test, simulate, and build solutions for airport baggage handling systems.

What does Vertech do?

Based in Phoenix, Arizona, Vertech designs and implements industrial automation solutions including traditional automation systems, SCADA systems, MES solutions, and OT networks. One of our industry focuses is airport baggage handling systems. A large airport can have hundreds of conveyors that need to be integrated and controlled by the system. Airport security requirements add layers of complexity requiring control systems that account for every bag on a conveyor and track suspicious activities, such as a bag suddenly disappearing or a new bag appearing from the middle of a conveyor. At Vertech we provide comprehensive solutions that handle all these details by personally writing everything from automation code in PLCs to the high-level systems that interface with airline data feeds.

What problem were you trying to solve?

A PLC (Programmable Logic Controller) is an industrial computer repetitively running logic that reads input sensors, implements operational behaviors and controls outputs. Inputs are control panel switches, push buttons, photo-eyes and the like. Outputs are motors, lights, warning horns and other devices. The PLC programmers have a problem, especially with a large system, of being unable to develop and test their code without the physical hardware being present. We had a need for a system that could simulate the conveyor hardware, provide relatively seamless connections with the PLCs, display the output conditions, and log what was going on without having to set up...

At Akka.NET’s inception, most of the server-side code samples we produced all demonstrated how to build so-called “headless” Akka.NET services as outright Windows Services primarily using libraries like Topshelf.

.NET has changed tremendously since then and become a truly cross-platform runtime that is capable of working with and within all of the amazing innovations that have sprung from the greater global open source community, such as Kubernetes and Docker. Thus, it’s time we modernize our guidance for how to build headless services in the age of .NET Core / .NET 5 and beyond.

We’ve produced a YouTube video demonstrating how to Host Akka.NET using IHostedService which demonstrates the modern approach to configuring and hosting stand-alone Akka.NET services:

This blog post compliments the YouTube video!

As part of the Akka.NET v1.4.15 release we’ve completely rewritten how dependency injection works in Akka.NET and introduced a new library: Akka.DependencyInjection. In this blog post we’re going to introduce Akka.DependencyInjection and some of the best practices for working with it.

We’ve also produced a brief YouTube video that demonstrates how to work with Akka.DependencyInjection too:

In our previous installment of “Real World Akka.NET Clustering”, we covered state machines - the tried and true tool for modeling event-driven behavior for business entities inside your domain. And we also demonstrated that using Akka.NET programming techniques such as behavior-switching it’s straightforward to implement them with actors.

In this post we’re going to take our discussion of real-world Akka.NET actors to a higher level and discuss how to use the process manager pattern with actors to model long-running, stateful workflows that naturally occur in all sorts of business domains.

Process Managers

What is a process manager? A process manager is a state machine used to direct a dynamic, stateful workflow. In the context of modern software applications most process managers tend to be responsible for managing distributed workflows that are executed across different services or multiple instances of a service.

Process managers are:

1. Reentrant - when we say “long-running” in the context of a workflow this often means durations measured in minutes, hours, or days - not seconds. Therefore, process managers are often programmed so they can be passivated (i.e. put to sleep) and recovered at a future point in time. We typically accomplish this using Akka.Cluster.Sharding in Akka.NET.
2. Durable - in order to be reentrant process managers must persist their state to a durable store of some kind, typically either a cloud filesystem or a database. This is a good fit for Akka.Persistence.
3. Driven by State Changes - process managers determine the next course of action in a workflow based on the output of the current and previous states. If we’re in error, perhaps we retry the most recent failed operation. If the operation failed irrecoverably, maybe we need to perform some reverisions and send a report back upstream.
4. Not Responsible for...