When you build a distributed system it is difficult to design good transaction guarantee mechanism. If your communication is asynchronous, you communicate with remote services using some messaging system. I guess you already know that network is not reliable, so your message can be lost. To guarantee message delivery you have to resend it when confirmation is missing. There are solutions to guarantee idempotence for the service receiving data. What I want to share is my idea how to make sending e-mail service as close as possible to the idempotence solution.
Workflow engines are very advanced tools and I saw a lot of projects where they created great business values. They sometimes simplify development. In this article I do not argue that you should not use them. My goal is to show you that there is an alternative – transformation from workflow into set of services distributed in the future.
SQL query engine is prepared to return correct results as soon as possible. But correctness means being correct from mathematical perspective. Problem that I will describe is obvious, but it is not what you sometimes expect from SQL engine.
While making plans for my travels, I was wondering how to protect my administrator access to remotely accessible NAS. I noticed that this device offers two-factor authentication mechanism, which should increase security. This article will focus on this specific high level implementation.