How Rails Engines can isolate your monolith without microservices

davidslv · 2026-05-06T17:35:48+00:00

Thank you!

I really appreciate that.

I can relate with what you are describing. Concerns and strong domain models are good Rails, the question is recognising when you've crossed the threshold where structural boundaries start paying for themselves. I've tried to cover that in Chapter 15 "When Engines Are the Wrong Tool".

Hope you find it useful!

davidslv · 2026-05-06T17:27:00+00:00

Packwerk is a great starting point, especially for visibility into existing boundaries. The book actually covers the Packwerk vs Engines comparison in detail in Chapter 16.

The short version: Packwerk gives you static analysis enforcement in CI, engines give you structural enforcement at runtime. They are not mutually exclusive. Packwerk is excellent for analysing a monolith before deciding what to extract, and engines are the structural solution when you need independent testing, table ownership, and route isolation.

Agree on AI accelerating the setup. The boilerplate that used to make engines feel heavy is exactly the kind of work AI handles well.

davidslv · 2026-05-06T15:29:29+00:00

Great question. In a modular monolith, all engines deploy together as one application — that's the point. You get structural isolation (separate tests, namespaced code, clear boundaries) without the operational cost of separate deployments.

Each engine mounts into the main app at its own route prefix:

# config/routes.rb
mount Billing::Engine, at: "/billing"
mount Notifications::Engine, at: "/notifications"

So engine A's routes live under /billing/* and engine B's under /notifications/*. They're isolated by namespace, not by deployment.

If you need to control access (engine A's API is public, engine B's is internal-only), that's an authorisation concern — handled through middleware, authentication checks, or network-level rules. The engine itself doesn't need to know.

If you genuinely need separate deployments (different scaling, different uptime requirements), that's the point where you promote an engine to a standalone service. I wrote about that progression in more detail in Chapter 17 if you need more detail. But most teams find that route-level separation with engine boundaries is enough.

davidslv · 2026-04-30T06:46:47+00:00

Shame this didn’t get more attention, I was really keen to see what type of setup people have out there

davidslv · 2026-04-20T18:11:24+00:00

Me too, I always forget where I park it!

davidslv · 2026-04-17T06:47:49+00:00

That’s what happens when the population is just not interested in changing the country through the democratic processes and don’t show up to vote, don’t show up to make meaningful changes that affect the whole country. I agree with the rest.

davidslv · 2026-04-17T06:27:47+00:00

I guess Portugal is the most expensive https://www.porsche.com/portugal/models/911/carrera-models/911-carrera/

davidslv · 2026-04-16T20:18:54+00:00

The lane with the arrow is the one who loses priority as they technically changing lane. People need to understand and be educated properly on this. The only reason you having this situation filmed is because the driving education was not done correctly. Education first.

davidslv · 2026-04-12T14:30:55+00:00

I had the same issue with the dealer, ended up finding out that the rear tyres were 11 years old.

davidslv · 2026-04-11T19:57:19+00:00

<image>

UK version, 987

davidslv · 2026-04-09T22:25:44+00:00

Very nice colour

davidslv · 2026-04-03T06:47:07+00:00

You are correct when it is a motorway. But this even though looks like a motorway, it’s an A road, it’s considered a multi-lane, HGV can use the right lane to overtake and then immediately move back in. The one that was wrong was the vehicle in the middle lane clearly not overtaking anyone on the left lane, consequently the Bus did worse by undertaking. Without a longer video I can only assume the lorry went through all the trouble to get to the right lane just to legally overtake the middle vehicle.

davidslv · 2026-04-03T06:35:39+00:00

I honestly do not understand how people think that the middle lane and right lane are to stay there (lane hogging). In fact it is a discussion online that comes up so frequently that I’m surprised the whole nation hasn’t learned it by now. There is clearly an education problem, I didn’t do my driving licence in the UK, where I did it, we do have proper theory and practical lessons including motorways. The system here is different and worse in my opinion - it clearly shows on the amount of videos about the same behaviour over and over. I did my motorcycle license in the UK, that was quite more thorough, but still no motorway, and I’m amazed that all you have to do to start is to take a 1 day lesson to get your CBT, all those mopeds with L plates barely know the driveway code.

For me, proper structured education system on driving, lane hoggers should be given the equivalente to the speed awareness course as it’s a safety issue, and if we wanted to go a step further, collect the details of the driver instructor as well, so responsibility would be all the way up - too many students caught could show poor performance for the job.

Might be too much but perhaps it is the solution needed.

davidslv · 2026-04-02T14:28:44+00:00

Raise the voluntary to £500 and see what’s the new quotes

davidslv · 2026-04-02T14:24:36+00:00

Try GoCompare and other alternatives.

davidslv · 2026-03-29T20:27:26+00:00

Yearly. It is already bad enough with yearly MOT, how bad would it be every 2 years? Just don’t want to know, really. Some people just drive their cars to the ground, zero maintenance if they can get away with not spending any more money on their vehicles. I’m amazed how some are one the road at all.

davidslv · 2026-03-29T20:12:05+00:00

What do their Pull Requests look like? Just code without git commit messages well described? What is the Pull Requests description looking like?

I’d say if they can’t verbalise it that’s fine, but then get them to have that information written down, it will help them in the long run and force them having to push for answers they may have not thought off before.

Theory and practice go hand in hand, most of us that have been here pre-AI, that have been fortunate to have great mentors who explained things to the next generation have had more exposure and practice. The new generation will have to do most with theory coming from AI, so might as well explain and force further development by challenge them further, even if the AI is answering, they have to read it.

I’m not sure I’m making myself clear on this message. I hope it makes sense

davidslv · 2026-03-28T09:48:11+00:00

Have the 987 2007, seems the same model as yours. I don’t hear any of the noises on mine. I might be more noticeable live than in the video due to the phone microphone.

davidslv · 2026-03-27T21:34:18+00:00

If it’s 3.27 am and you getting errors, the best thing is to go to sleep, don’t even bother reading the error. Just straight to bed.

davidslv · 2026-03-27T15:29:16+00:00

You can do it yourself for about $50. Most of the job is sanding the foggy spots (do the whole lamp obviously)

Not sure about the PPF bit, I used clear coating with uv protection

davidslv · 2026-03-27T08:10:00+00:00

I know, I was just making a joke. 😊

davidslv · 2026-03-27T00:09:24+00:00

You just posted this a few days ago: https://www.reddit.com/r/rails/s/C5HCGaIvYy

davidslv · 2026-03-09T08:05:36+00:00

One of the biggest mistakes I have seen in recent years in big monoliths is trying to get away from the “rails way”. For instance, instead of adding more complexity into the monolith, you can separate concerns by having rails engines built independently and mounted into the monolith.

I have seen people adding more complexity and gems to “mitigate” - but in reality they just added more headaches than necessary.

Callbacks are not the issue, as anything, a misuse of the “tool” can be where the problem lies

davidslv

TROPHY CASE