molina/README.md

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Molina documentation

Molina is a service I run on my own machine. You hand me your software as a container image, and nothing is installed on yours. I make its disk, network and clock fail the way real ones do, then check the promises your software has to keep.

So far I have run experiments on a disk that says saved before it is, a cluster of servers with its network split, a program with racing threads, and a database whose power was cut at 40 different points.

Molina is for a business owner or head of engineering whose product depends on a database or on several servers working together, and for the engineers who run that product. They are responsible for databases, distributed systems, infrastructure and data durability, where losing data a customer was told was saved, breaking a consistency promise or being unable to reproduce a failure has serious consequences.

The sales page is short. These pages hold the detail.

How it works: from a container image to a replay code, in four steps and one picture.
What you get at the end: a worked example, from my own experiment, in the order your engineers would read it.
FAQ: the questions buyers ask me, in plain words.
Glossary: replay code, promise, network split, saved write and the other words, in everyday terms.
How to read a result: what the labels on a record mean.
What it cannot do: the software I cannot run and what I cannot promise.
How I treat your data: what I do with your files and what can read them.

How exact is the replay?

Replay matched exactly in five of my runs. Replay is not yet measured on your software until I run it.

An Akka.NET cluster with its network split: in 3 of 3 pairs, all 1,476 network messages had the same outcome, delivery time and contents, and the same 42 were cut. Standing: MIGHT. The record
A .NET program with four racing threads: 96 restored copies, 90 counted, none differed. Standing: MIGHT. The record
Postgres on a disk that says saved before it is, in exact mode: 3 of 3 replays byte for byte identical in console, timings and switch log. The switch log was empty: no network message crossed the switch. Standing: MIGHT. The record
A NATS pair with a split in virtual time: 3 of 3 replays, all five files byte for byte identical; with another replay code, 0 of 5 files matched. Standing: MIGHT. The record
Akka's own test, NodeUpSpec: 36 of 36 copies byte for byte identical on an idle host and 36 of 36 on a loaded one. Standing: UNRATED. The record

What I ran

Each record says what it shows and what it does not show, and gives the conditions where they fit.

The short version, on the Molina page

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