We've got an Excel spreadsheet floating around right now (globally) at my company to capture various pieces of information about each countries technology usage. The problem is that it goes out, gets changes, but they're never obvious, and often conflicting - and then we have to smash them together. To me, the workbook is no more than a garbage in/garbage out type application waiting to be written.
In a company that has enough staff and knowledge to dedicate to Enterprise projects, for some reason, agile and language/frameworks such as Rails, Grails, etc. are frowned upon. That said, I can't help but think that this is almost a perfect fit for the need, given the scaffolding features for extremely simple implementations of capturing raw fields with only a couple lookups (i.e. a pre-defined category). I'm thinking this would be considered a very appropriate use of these frameworks.
Has anyone worked on these types of quick and dirty apps before in normally large-scale, heavy-handed enterprise environments with success? Any tips for communicating this need/appropriateness to non-technical management?
The only way to get this implemented in a rigid organization is to get this working and demo it -- without approval. It's very hard for management to say no to a finished project.
I work for a really big company & have written many utility apps based on Rails (as well as contributed to some larger Rails projects). That said, the biggest concern is not the quality of the app, but who's going to support/maintain it when you leave or get hit by the bus.
IMHO, The major fear that an enterprise organization has - especially if the application becomes more critical to it's core business - is how to support it. If it doesn't fit into it's neat little box of supported technologies, it's less likely to happen.
Corporations have been bitten by this many times in the past & are cautious when bringing in new technology.
So, if you can drum up more folks to learn Ruby/Rails in your group (or elsewhere in your company), you may be able to make a good case for it. Otherwise, sad to say, your probably better off implementing something on Sharepoint :-(.
If you already have a Java infrastructure, then creating a Grails app will require little to no additional IT ramp up to support and maintain. The support and maintenance cost and effort should be the same as for a Java application (i.e. Grails apps run on Tomcat, use the same JVM, use the same diagnostic/profiling tools, etc.).
In my experience, larger IT organizations have a harder time supporting Ruby when its not already in the toolchain because its a new language, new deployment environment, and requires a considerable amount of support and maintenance ramp up.
I would develop a minimal viable product, then make friends with someone in IT who can help you deploy it into a staging or production environment. Then get a few of the users to hop on board and test it like its a Beta product. After that, open it up to a larger audience.
So as others have said, forgiveness over permission, but be smart about the impact on the IT organization.
Related
I want to learn a framework that promotes good programming practices and is respected by the programming community.
However, I also want a framework that I can use for a day job.
Which one would you recommend?
This question comes from my experience of learning the basics of Django because it was highly acclaimed by developers on Stack Overflow and Hacker News. However.. there's hardly any jobs in my area (NYC) that are asking for Django developers.
As a long-time ASP.NET guy, I've recently gone through a similar decision process to figure out what other web frameworks I should try. Here's what I learned so far which may apply to your case too:
framework/platofrm choices (and hence job opportunities) are highly regional-- the Bay Area job market differs alot from what you'll find in NYC, Chicago, Montreal, or London. Look at local job listings (craigslist and indeed are good places to start) to get a good sense at what's in demand.
similarly, usage varies alot based on the size and type of company. if you want to get a job in a large company, Spring MVC and ASP.NET MVC may be your best bets. In small companies, DJango and (especially) Rails seem to be on the rise.
usage also sometimes varies by industry. for example, many HR apps seem be to .NET based, while financial/banking apps seem to favor Java. if you want to work in a particular industry, check out what up-and-coming companies in that industry are using.
when investing your scarce time in learning something new, favor technologies which are on the upswing of the adoption curve (e.g. Rails) rather than frameworks with wider adoption which may not be growing as fast. Also be wary of very early or niche frameworks which may not ever gain wide adoption.
the one common thread between most (or almost all) frameworks gaining in popularity is that they're MVC frameworks and rely heavily on a solid understanding of REST. Learning those concepts in depth is a good idea.
before deciding to invest a lot of time in one framework, gain a basic understanding of several of them, so you can get a reasonable sense of what you like and don't about each-- and so if you end up applying for a job using a framework you haven't learned, at least you'll be able to talk intelligently about it.
If you focus on what you enjoy, you'll be more motivated to learn it. For example, personally I found Rails (regarless of employment opportunities) more interesting than Spring or Django, so I decided to focus on Rails first. Others may have different impressions-- follow your programmer instincts. That said, there are often few jobs using technologies you find fascinating, so try to strike the right balance: technology you like that many companies are actually hiring people to use!
once you answer the basic "what framework" question, there are many more questions lurking, including picking a javascript framework, validation framework, an ORM, etc. Don't worry too much about those choices yet-- when starting, just pick the default implementation for your framework. But as you get more advanced, the same argument about frameworks also hold for those other things-- e.g. it's useful to know a few ORMs.
Personally, I decided on this approach:
continue building stuff in what I knew best (ASP.NET) but transition all work to ASP.NET MVC, where I can better understand MVC and REST concepts which apply cross-platform
learn JQuery (again, platform neutral)
blow off the ORM choice alltogether for now-- too many other things to worry about
build a few projects in Rails, which is the framework I see used most in the newer SF-Bay-Area startups I've been looking at
learn the basics (e.g. read a book or two, try a few samples) about Python/Django, Java/Spring, and Groovy/Grails.
I've encountered real projects at cool, small companies using Django, Ruby on Rails and (eiuw!) even Zope. .NET is for teletubbies - I've only ever heard of it being used by big corporations that don't know better.
I would say that knowing two or three is better than knowing one that is widely used because you will gain a better understanding of how it works as a concept. For instance if you've only used Java, there is something probably missing in your understanding of OOP, because you're pigeon-holed into thinking about it in one way. If you already know Django though you Spring would probably be a good compliment to that.
i'd probably say ASP.NET MVC. I always see lots of .NET jobs around and this seems to be a solid framework which i think in fact powers all the stackoverflow family. As a PHP developer i must also make a mention of Zend Framework which is used by a number of big sites including bbc.co.uk and is now frequently mentioned in advertisements for PHP jobs.
I want to learn a framework that promotes good programming practices and is respected by the programming community. However, I also want a framework that I can use for a day job.
Sorry to be the bearer of bad news here, but those two desires tend to conflict. IMHO most business managers tend to go for (ugly) rapid development on top of CRMs or other higher-level 3rd party codebases. Building elegant websites from the ground up mostly happens in startups, or true web companies where the website is the sole product. There are not that many of those companies; and many of those that seem to fit are actually a mess on the inside, i.e. due to time pressure, messy legacy code and many other reasons you often don't get to write according to "good programming practices" anyway.
I agree with Kaleb Brasee that Java and .NET are the two main platforms when job availability is a priority.
Every job market is unique, so look at job openings in your area, or call a handful of recruiters and ask what they see a need for / could easily place you in a junior position for. What I'm seeing is that Microsoft Sharepoint is in demand, and a few other regional CMS'es are in demand (in Denmark I see Sitecore regularly).
I think ASP.NET MVC 2.0 together with MVC Areas and ASP.NET Dynamic Data will have a good story, a good solution, for many of those bosses who want rapid development. And I think the resulting code could be quite okay, or at least not bad compared to many of the "CMS beaten into something else" sites that exist. But this is a brand new thing for the .NET platform, and it will need to be sold to the decision makers first...
Bottom line: If you want job security first and foremost, then look at large CMS's like Sharepoint, and work on other technologies in your spare time. Optionally you could take a job at a startup / a web company later; but look before you leap.
Have you tried Spring MVC? Many companies do use Java for web-apps (or .NET) and web service based applications.
Since you mentioned Ruby on Rails, you might want to learn Ruby on Rails. It has got some good programming practices in it and a very well thought architecture. The Ruby community itself have also (in my personal opinion) created very innovative frameworks and highly favor testing and quality. You can see this by the innovative testing framework like Cucumber, webrat, shoulda, coulda, rspec, test/spec. Many startups also uses Rails as their platform, so it should be easier for you to get a job. You can start looking at Working With Rails and 37signals job board. So there is a good ecosystem inside Rails and Ruby community.
But the downside of Rails compare to Django is mainly there are too much magic (less explicit) and the docs is not as good as Django. If you want to get a Django job, try looking at several news site because Django grew up from a newspaper site so it is adopted alot in news based sites.
I would recommend ASP.NET MVC, Ruby on Rails, or Python/Django, they all seem to be popular and successful, and based on the MVC paradigm which is definitely the right tool for the job when it comes to the web.
.NET and Java are by far the 2 largest platforms used by employers, and hence the most in-demand when searching for a job. Java has a few popular frameworks, with JSF, Spring MVC and Struts all seeming to be about equal in demand. I don't use .NET, but from what I've seen, ASP.NET and ASP.NET MVC are the major ones.
I would say that most of the frameworks mentioned here promotes good practices. But that doesn't neccesarily mean that the companies using those frameworks are actually following those good practices! In fact most probably aren't. So don't expect too much.
You see, places like Stack Overflow, Hacker News etc. are a great way to connect with people who really care about their craft. Sadly this is a minority. There are millions of programmers in the world. Most of them suck. The code they write sucks. They don't care. They are not interested in improving their skills. They just want to learn the bare minimum required to collect their paycheck, go home, feed the dog, spend some time with the family, watch some TV, go too bed and do it all over again the next day.
Okay that was a bit harsh :) What I'm getting at is that you are probably better off asking this question to some of the managers at the companies where you would like to work. My guess is that most of them will answer .NET or Java. If you are up for a laugh ask them why they chose that particular technology over something else, and see how many buzzwords they throw at you ;)
What language, framework, and hosting considerations should one make before starting development of a scalable web application?
The most important consideration is not to over-engineer to the point that it gets in the way of building and launching something. Analysis paralysis is the single biggest inhibitor to productivity, progress and results.
Yes, do some planning. Pick a framework. Perfection in a framework will be impossible to find because it doesn't exist, partially because you don't know what you need until you build it anyways. Chances are, if you pick something, it will be better than picking nothing.
Yes, try to pick flexible, inter-operable tools for where you see yourself going.
Yes, look for a good built-in feature set where you see yourself going in the next 6-18 Months. Trying to look beyond that is not really realistic anyways as most projects change so much anyways going towards the first release.
So, pick what you're comfortable with or what is familiar. Don't follow the crowd, do what gets you the best results, quickest, and often. Understand that you might have to change in the future. So, whatever you build now, try to use unit testing so you can re-factor if ever needed.
If what you're building is going to be super successful, it will be a great problem to have, and an easy one to work on once it's making money as you'll be able to get other talent to help you.
Share what you end up picking and why for your situation -- it helps the us learn from you too!
Don't necessarily marry yourself to one language or framework. It may be that some parts of your site work better with different languages and frameworks than others. For example, all of 37signals' sites are based on Ruby on Rails, but they recently wrote a blog post about how the underlying technology of one is actually written in Erlang now because it's much easier to do concurrency that way.
Obviously there's a level of complexity where things turn into a mishmash, but using the right tool for the job — even if that means different tools for different jobs — can simplify things.
Firstly on language, it largely doesn't matter. PHP, Java and .Net being probably the biggest three are all proven in the sense that they run some of the largest sites on the Web so don't listen to anyone who tells you one is more suited than any of the others.
Some might also put Ruby and Django/Python in this list. I have nothing against them but I'm not aware of any big (say top 50) sites using either.
Hosting considerations depend on how low you want to start but basically the order is:
Shared;
Virtual Private Server;
Dedicated.
Scalability will largely be about your application's design than any language, framework or provider. Efficient database schema, efficient delivery and use of Javascript/CSS and in-memory caching are all issues common to any language or framework.
Language - I'd recommend something with good frameworks and good testing libraries like Perl or Java.
Framework - it depends on what do you plan to do. If you start with a hosting that does not allow FastCGI, it is best to avoid such frameworks like Catalyst or Rails. That's why I love CGI::Application (primarily Perl, but ported to other languages too) - it can run as CGI, FastCGI or mod_perl. For development it can be run from it's own web server.
Hosting - nothing is better than you own server. It can be your own server, leased server or virtual server. But you can start with cheapest hosting and when you need more, you should be able to afford it.
It depends.
Start by looking at your requirements (Functional or user defined) (Non Functional - aspects that describe your desired system link text)
Next I would clarify what it means to have a scalable web application. Define it as test cases that can be clearly tested (must support X page views / second with response time < Y seconds).
Once I had those pieces in place I would look at what type of skills my development team can support (for the intial project and on going maintenance). Then find some case studies of applications out in the wild that use similar language or framework. If someone else has made a specific language / framework scale then chances are good that you can too.
Finally go out and look for some hosting providers that support your chosen language, framework and requirements.
I'm a big fan of ruby on rails, and it seems to incorporate many of the 'greatest hits' of web application programming techniques. Convention over configuration in particular is a big win to my mind.
However I also have the feeling that some of the convenience I am getting is coming at the expense of technical debt that will need to be repaid down the road. It's not that I think ROR is quick and dirty, as I think it incorporates a lot of best practices and good default options in many cases. However, it seems to me that just doesn't cover some things yet (in particular there is little direct support for security in the framework, and plugins that I have seen are variable in quality).
I'm not looking for religious opinions or flamewars here, but I'd be interested to know the community's opinion on what areas Rails needs to improve on, and/or things that users of Rails need to watch out for on their own because the framework won't hold their hand and guide them to do the right thing.
Regardless of framework the programmer needs to know what she's doing. I'd say that it's much easier to build a secure web application using something as mature, well designed and widely adapted as Ruby on Rails than going without the framework support.
Take care with plugins and find out how they work (know what you do, again).
I love Rails too, but its important for us to understand the shortcomings of the framework that we use. Though it might be a broad topic addressing these issues wont hurt anyone.
Aside from security issues, one other big issue is DEPLOYMENT on Shared Hosts. PHP thrives in shared hosting environments but Rails is still lagging behind.
Of course most professional Rails developers know that their apps need fine-tuned servers for production and they will obviously deploy on Rails-Specific hosts.
In order for Rails to continue success the core team should address this issue, especially with Rails 3.0 (Merb +Rails) coming..
An example of this is simple: I have a bluehost account, and i noticed the Rails icon in my cpanel. I talked to the bluehost support and they said its more or less a dummy icon, and that it doesn't function properly.
Having said that any professional who wanted to deploy a Rails App would not use bluehost. , but it does hurt Rails, when hosts say that they support it and then users run into problems which their support know nothing about..
The article you refer to defines technical debt as
[the] eventual consequences of
slapdash software architecture and
hasty software development
With rails, any development that is not test driven incurs technical debt. But that is the case with any platform.
At an architectural level Rails provides some deployment challenges. A busy site must scale with lots of hardware or use intelligent caching strategies.
My advice to anyone adapting Rails would be to:
use TDD for all your development
verify the quality off any plugin
you use by reading its tests. If
they are not clear and complete,
avoid the plugin
read "Rails
Recipes" and "Advanced Rails
Recipes" (Advanced Rails Recipes has
a good recipe for adding
authentication in a RESTful way)
be prepared to pay for hardware to scale your site (hardware is cheaper than development time)
From my experience, by far the biggest tolls you end up paying with RoR are:
Pretty big default stack (not counting plugins you might be using)
Updating models tends to be a pain in the ass, at least in production servers.
Updating Rails or Ruby themselves is a bit more complicated than it should, but this differs depending on your server setup.
As ewalshe mentioned, deployment is sometimes a drag, and further down the road, should you require it, scaling gets a bit iffy, as it does with most development frameworks.
That being said, I'm an avid user of RoR for some projects, and with the actual state of hardware, even though you do end up paying some tech debt to using it, it's almost negligible. And one can hope these issues will be reviewed eventually and solved.
With any level of abstraction there is a bit of a toll you pay - genericized methods aren't quite as fast as those specific to something built just for your purpose. Fortunately though, it's all right there for you to change. Don't like the query plans that come out of the dynamic find methods? write your own, good to go.
Someone above put it well - hardware is cheaper than developers. I'd add "at a sufficiently low amount of hardware"
I'm reading Deploying Rails Applications and recommend it highly to answer your concerns.
The book is full of suggestions to make life easier, taking a deployment-aware approach to your Rails development from scratch, rather than leaving it to later.
I don't think the choice of RoR implies a technical debt but just reading the first few chapters alerted me to practices I should be following, particularly on shared hosts, such as freezing the core rails gems so you can't be disrupted by upgrades on the host.
The 30-page chapter on Shared Hosts includes memory quote tips such as using multiple accounts (if possible) with one Rails app per account. It also warns about popular libraries such as RMagick possibly pushing your memory size to the point where your processes are killed (such as a 100MB limit, which it suggests some hosts periodically apply).
Tomorrow, I will meet a client that is not working in technology but might ask if RubyOnRails is the right choice for his site. He might think that there's not enough RoR programmers and that he will be "hostage" of the language.
I have good reasons to use RoR and the client has good reasons to like it (it costs less!).
Do you have "official" sources I could show them?
Using a framework ensures that the "next guy" can pick it up quickly
Rails has reduced my workload by 80% over hand-coding.
Huge, active, friendly community to draw upon
Self documenting testing frameworks
It uses Ruby, which is super easy to learn in a pinch
Open source language, framework, and database that uses an open source OS. FREE sells.
This is, in some sense, a variant on the "bus hit factor" problem. Any app, once developed, is pretty much "hostage" to the language, the question is whether it is also "hostage" to the single developer who wrote the app. I think that RoR is a perfectly reasonable choice for development, but the issue is really how many developers in your local area are available to take this over if you happen to "get hit by a bus." If the customer is willing to work with someone remotely, this becomes much less of a problem. To reassure him, though, I'd first look to the local scene and find out about local Ruby developer groups. The presence of active, local developer groups is one measure that might convince him.
If, on the other hand, he's concerned that RoR will not continue to be viable in the future that is a slightly different issue. Again, I think you're ok -- you may want to point out other applications that are written using RoR as an indication of continuing pressure to improve both the language (Ruby) and the framework (Rails). You can find a lot of this information at http://rubyonrails.org/.
"might ask if RubyOnRails is the right choice for his site. He might think that there's not enough RoR programmers and that he will be "hostage" of the language."
Have you considered the possibility that these are valid concerns that should be taken seriously?
"I have good reasons to use RoR"
How does that help your client, though?
"it costs less!"
Does it? Do you have any specific evidence to support that assertion? Have you factored in hosting costs? Rails on MRI uses a lot of RAM. You're probably in Java territory or worse. Depends on the app and the load of course. Phusion Passenger (mod_rails) has improved the situation somewhat, but it's still an issue.
As mentioned by others documentation is a "HUGE" issue. Ruby and Rails official docs are sparse, to put it kindly. The community tends to rely on paper books which become outdated and misleading in a matter of weeks, thousands upon thousands of unreliable, contradictory blog posts, and screencasts which also suffer severely from the "quickly-outdated" problem. Don't think PeepCode is going to save you.
I would still consider advising a client to use Rails because the claims of programmer efficiency are more or less true, sort of, but I'd do so with extreme caution and I'd let him know the downsides.
Documentation is HUGE when it comes to open-source projects.
One thing you could do would be to explain to your client that it will cost them much more to have you and your developers spend hours and days searching for documentation on some other open-source framework that is less used and supported. Explain that there may not be as much ROR developers out there as there are PHP developers per say, but the fact that there's such a great amount of documentation and information about ruby and rails makes it exponentially easier to for any open-source developer to learn and use the framework.
There would be some things I would try to convince the client-
Ruby Community is huge
Ruby is mature enough
Ruby works with most database systems.
Rails is a product based on an Idea(MVC) most other platforms have embraced.
Improved readability and testability of code.
COSTS LESS!!
Migration methodology in RubyOnRails
If you want you can even target the Java Platform using JRuby and Java Platform is a pretty respectable platform.
Show some cool RoR applications.
Explain how you could be Agile!
I know so well clients not agreeing when you dont have a big company backing a technology.
The "cost less" feature of RoR is debatable, I agree with you. But in my case, I have a complete RoR-ready environment and I know that I can charge less for a RoR app than any PHP app that I could do.
The hardware/software environment for PHP and Rails are almost the same... so is the price of it. What will cost less for the client is the robust environment that we built.
That's the "cost less" feature. I'm not talking about about memory comsuption or anything else. It all can be bought for almost nothing.
This depends a lot on location. If RoR developers are plentiful and work for prices comparable to other programmers then you can use that to help sell Ruby.
For a client one of the main concerns is cost. Perhaps he is concerned about maintenance costs of finding and paying for a RoR developer, not the cost of the technology.
I know a web shop who was bitten by the relative 'newness' of RoR. They hired a developer to make a site and that developer use RoR. After the project the developer left. In our area RoR developers are not only scarce, they charge more than any other type of web developer. In this particular case the web shop ended up losing their client. The last I checked their client's web site is in PHP.
I'm not trying to say RoR is bad and I think that's an extreme case, but make sure to consider the client's concerns. The cost of maintenance is a very valid concern.
I have a memory of talking to people who have got so far in using Ruby on Rails and then had to abandon it when they have hit limits, or found it was ultimately too rigid. I forget the details but it may have had to do with using more than one database.
So what I'd like is to know is what features/requirements fall outside of Ruby on Rails, or at least requires such contortions that it is better to use another more flexible framework, even though you may have to lose some elegance or write extra boilerplate code.
Rails (not ruby itself) is proud to be "Opinionated Software".
What this means in practice is that the authors of rails have a certain target audience in mind (themselves basically) and aim rails specifically at that. If X feature isn't needed for that target audience, it doesn't get added.
Off the top of my head, things that rails explicitly doesn't support that people may care about:
Foreign keys in databases
Connections to multiple DB's at once
SOAP web services (since rails 2.0)
Connections to multiple database servers at once
That said, it is very easy to extend rails with plugins, and there are plugins which add all of the above functionality to rails, and a lot more, so I wouldn't really count these as limits.
The only other caveat is that rails is built around the idea of creating CRUD web applications using MVC. If you're trying to do something which is NOT a CRUD web app (like twitter, which is actually a messaging system, or if you are insane and want to use a model like ASP.NET webforms) then you will also encounter problems. In this case you're better off not using rails, as you're essentially trying to build a boat out of bicycle parts.
In all likelihood, the problems you will run into that can't just be fixed with a quick plugin or a day or 2 of coding are all inherent problems with the underlying C Ruby runtime (memory leaks, green threads, crap performance, etc).
Ruby on Rails does not support two-phase commits out of the box, which maybe required if your database-backed application needs to guarantee immediate consistency AND you need to use two or more database schemas.
For many web applications, I would venture that this is not a common use-case. One can perfectly well support eventual consistency with two or more databases. Or one could support immediate consistency with one database schema. The former case is a great problem to have if your app has to support a mondo amount of transactions (note the technical term :). The latter case is more typical, and Rails does just fine.
Frankly, I wouldn't worry about limits to using Ruby on Rails (or any framework) until you hit real scalability problems. Build a killer app first, and then worry about scalability.
CLARIFICATION: I'm thinking of things that Rails would have a hard-time supporting because it might require a fundamental shift in its architecture. I'll be generous and include some things that are part of the gem/plugin ecosystem such as foreign key enforcement or SOAP services.
By two-phase commits, I mean attempting to make two commits to physically distinct servers within one transactional context.
Use case #1 for a two-phase commit: you've clustered your database, so that you have 2 or more database servers and your schema is spread across both servers. You may want to commit to both servers, because you want to allow ActiveRecord think do a "foreign key map" that traverses across the different servers.
Use case #2 for a two-phase commit: you're attempting to implement a messaging solution (sorry, I'm J2EE developer by day). The message producer commits to the messaging broker (one server) and to the database (a different server).
Also found some good discussion about the limits of ActiveRecord.
I think there is a greater “meta-question” here, that could be answered and that is “when is it OK to lean on external libraries to speed up development time?”
Third party libraries are often great and can drastically reduce development time, however there is a major problem, Joel Spolsky calls this “the law of leaky abstractions.” If you look that up on Google his post will come up first. Essentially this means that the trade off in development time means that you have no idea what is going on under the covers. So when something breaks you are completely stuck and have very limited methods of debugging. This also means that if you hit one of the features that are simply unsupported in RAILS, that you really need, you’ll have no next step except to write the feature yourself, if you’re lucky. Many libraries can make this difficult to do.
We’ve been burned badly in my dev shop by this issue. Our solutions worked fine under normal load, but we found that the third party subscription libraries that we were using simply could not stand up to the kind of load that we experienced once our site started to get a large number of concurrent users. This puts us in a very difficult place; essentially we have to rewrite the entire subscription service ourselves, with performance in mind. Doing this means that we’ve wasted all the time that we spent using the library.
Third party libraries can be great for small to medium sized applications; they can drastically reduce development time and hide complexities that aren’t necessary to deal with in the early stages of development. However eventually they will catch up with you and you’ll likely have to rewrite or re-engineer your solution to get past the “law of leaky absctractions”
Ruby don't have a functionality like IsPostBack in ASP.Net
Orion's answer is right on. There are few hard limits to AR/Rails: deploying to Windows, AR connectors that aren't frequently used, e.g. Firebird, ), but even the things he mentioned, multiple databases and DB servers, there are gems and plugins that address those for legacy, sharding, and other reasons.
The real limitation is how time-consuming it is to keep on top of all the things that rails devs are working on, and researching specific issues, given how many blogs, and how much mailing list volume there are.