I get asked this a lot, so here are my thoughts.
First, two disclaimers -- I'm not a doctor. Second, I've got a lot of data, but it's all mine so it's all anecdote. All I can back it up with is a few friends who have similar or identical gear to what I use.
So with that said, here we go.
First, alcohol (drinking alcohol now, not the non-potable versions!) are ethanol. They are a form of carbohydrate.
But alcohol is a special carbohydrate. Unlike the common sort in foods ethanol is preferentially metabolized -- that is, it is burned first before other carbohydrates. This is why you get drunk (instead of it "mixing" with all the other carbs and being taken up slowly, which would mean you'd have to drink on an empty stomach to get drunk at all) but at about one drink per hour, you also burn it off at the same rate no matter how much food you eat.
Like all other carbohydrates, however, ethanol also produces the same sort of boost/crash response that you get from other fast carbs, and in fact since it burns first it's arguably the fastest carb. This is why when you're drinking you often want food and is why "bar food" is inevitably high in carb content (e.g. french fries, etc); the bar owners are not stupid and they sell what people want to buy.
There are two basic problems with drinking alcohol in any amount as it relates to a keto lifestyle. The first is that booze inherently is anti-ketogenic, although if you keep it to one drink in a day you can remain in a ketogenic state and have that one drink, provided you are performing some amount of exercise (so as to keep glycogen stores very low.) The problem is that the second drink, and any non-keto food you might consume due to the cravings that alcohol does produce, is almost-certainly enough to knock you out of a ketogenic state.
There used to be a book out there from the early 1900s called "The Drinking Man's Diet." Unsurprisingly, it called for consumption of essentially zero carbohydrate; the reason is that alcohol consumption greatly potentiates weight gain if you eat carbohydrates. Why? Because it's metabolized first and thus the rest of the carbs you take in wind up being stored as glycogen and, if your glycogen stores fill it goes directly on your body as fat.
So that's the keto-related bad news, basically. But unfortunately the bad news doesn't end there and it's not ketogenic-specific.
I own a Fenix 5x, which I wear basically all the time (except when doing some sort of work that might damage it, such as working on my car, and when it needs to be charged) including overnights. It's an incredible piece of equipment which I bought mostly for its performance tracking under exercise and its mapping functionality, which is a safety feature when I am hiking in the backcountry ("never lost" as long as it can see the sky and has power.) No, it's not a substitute for a map, compass and knowing how to do land nav, but it's convenient and, in my opinion, was well-worth the investment.
It also gives me a hell of a lot of data across my entire day. One of the things it allows me to do is track the quality of sleep, heart-rate variation (which maps to your stress level) and resting heart rate. And this is where the second piece piece of bad news comes from.
I can tell you from looking at that RHR and HRV (stress) level during my time sleeping on which days I have had zero alcohol intake, on which days I had one drink, on which days I had two, and on which days I had more. The "more" doesn't matter; once you pass the second one in a day from a stress point of view you may as well get hammered. My accuracy rate just looking at this piece of information alone is astoundingly high -- and when it's wrong, it's never wrong on the low side (that is, indicating less stress than my booze intake indicates.)
The first drink will raise my resting heart rate by a point or two and delay my systemic stress level from dropping into the lowest category by a couple of hours. The second by two to four points and costs me half the night in terms of getting into that "resting" state from a stress point of view. Third and beyond? You're screwed in terms of actually getting anything that's called "rest" when you sleep.
This has profound implications if you are interested in athletic performance as well. There's simply no way you will be well-rested and able to perform at peak capacity if you've had anything to drink for two to three days prior to the event.
This is utterly repeatable, every time, has been since I've owned this unit from the first day forward and anyone that has access to that data is going to be able to figure it out without knowing anything else about you. A couple of friends of mine who have similar units have told me that they have identical results, and I've confirmed this as they've let me look at their data briefly and told them which days they went out to the bar. I was right -- every time.
For this reason putting such data in the "cloud" and allowing anyone else access to it is a profoundly bad idea. You don't need an AI to process this, just a pair of eyeballs!
It would be utterly trivial to determine your consumption of booze and "box" you from which it would then be trivial to do things like charge you more for insurance.
The above, by the way, assumes your alcohol is liquor and there are no sugars in whatever you mix it with, if anything. Straight-up Scotch, vodka-and-(diet) tonic, etc. Beer and wine also contains carbs that are not from the alcohol; those have to be counted too and it's almost-impossible to know what the non-booze carb content is with the exception of a handful of "light" beers that advertise it -- because unlike actual food the manufacturers don't have to tell you, and they typically don't. When it comes to craft beer you may get away with one pint glass (or 10oz for high-gravity) of beer but you won't get away with the second in terms of ketosis. The same issue presents itself when it comes to wine.
So if you're asking whether drinking alcohol is compatible with living a ketogenic lifestyle, the answer is "maybe." The maybe is that if you are actively trying to lose weight then no, it isn't, and by the way, it doesn't matter what form of food intake you're using in that case because alcohol will poison all of them in terms of weight loss. The old saying that "he has a beer belly" is not bull****, in short. One of the worst ways to sabotage your metabolic systems is to screw with your hunger regulation -- while it's possible to ignore that it takes an amount of willpower few possess.
If you are very studious about avoiding any sort of other carbs, except for nutrient-dense green vegetables, then you can probably remain in a ketogenic diet with one drink a day, assuming you are an average-height male. Women have it tougher simply because on average they're smaller and alcohol is typically not "sized" in terms of the size of the drink to match body size and mass. This means that for most women that first drink is going to be borderline. Your odds of remaining in a ketogenic state improve if you are engaged in a material amount of vigorous exercise daily (defined as at least 15 minutes of effort in heart rate zone 4 or 5) as well.
But beyond one drink it doesn't matter if you're trying to live a keto lifestyle. You will get knocked out of a ketogenic state with the second beer or mixed drink essentially every single time and it is likely to require 48 hours or even more to return to it.
So yeah, if you have one night a week you have a few beers and such you basically took a 7-day ketogenic state and turned it into a 3-4 day one. That's half. If you're already where you want to be in terms of body mass and metabolic state you can get away with that once a week and probably not harm yourself all that much.
But if you do that twice in a week you can forget it.
The worse news, however, is that ketogenic or not that second drink costs you substantially in terms of impacting your overall body stress level and quality of sleep. The third one destroys both and it will require 48-72 hours of abstinence before things are back to normal.
This, incidentally, is wildly out of kilter with what the so-called medical "experts" will tell you. They all say that one drink a day is not harmful and may even be protective; that the second one is probably "neutral" and real serious harm starts with the third (and gets rapidly worse with increasing quantity.)
The trivially documented disruption starts with the first drink, the second does very material damage to the quality of your rest and beyond that you may as well get rip-roaring trashed in terms of cardio and overall systemic stress.
I'm sure a far more-strict analysis is almost directly dose-dependent -- for example, the damage done to your liver. But here I'm not focusing on the long-term chronic effects from drinking too much -- those are both well-known and basically impossible to argue with.
This is simply looking at the data in the context of consumption of "routine" amounts of alcohol if you are trying to live a healthier metabolic lifestyle.