Update 4: Heroku versus GAE & GAE/J
Update 3: Heroku has gone live!. Congratulations to the team. It's difficult right now to get a feeling for the relative cost and reliability of Heroku, but it's an impressive accomplishment and a viable option for people looking for a delivery platform.
Update 2: Heroku Architecture. A great interactive presentation of the Heroku stack. Requests flow into Nginx used as a HTTP Reverse Proxy. Nginx routes requests into a Varnish based HTTP cache. Then requests are injected into an Erlang based routing mesh that balances requests across a grid of dynos. Dynos are your application "VMs" that implement application specific behaviors. Dynos themselves are a stack of: POSIX, Ruby VM, App Server, Rack, Middleware, Framework, Your App. Applications can access PostgreSQL. Memcached is used as an application caching layer.
Update: Aaron Worsham Interview with James Lindenbaum, CEO of Heroku. Aaron nicely sums up their goal: Heroku is looking to eliminate all the reasons companies have for not doing software projects.
Adam Wiggins of Heroku presented at the lollapalooza that was the Cloud Computing Demo Night. The idea behind Heroku is that you upload a Rails application into Heroku and it automatically deploys into EC2 and it automatically scales using behind the scenes magic. They call this "liquid scaling." You just dump your code and go. You don't have to think about SVN, databases, mongrels, load balancing, or hosting. You just concentrate on building your application. Heroku's unique feature is their web based development environment that lets you develop applications completely from their control panel. Or you can stick with your own development environment and use their API and Git to move code in and out of their system.
For website developers this is as high up the stack as it gets. With Heroku we lose that "build your first lightsaber" moment marking the transition out of apprenticeship and into mastery. Upload your code and go isn't exactly a heroes journey, but it is damn effective...
I must confess to having an inherent love of Heroku's idea because I had a similar notion many moons ago, but the trendy language of the time was Perl instead of Rails. At the time though it just didn't make sense. The economics of creating your own "cloud" for such a different model wasn't there. It's amazing the niches utility computing will seed, fertilize, and help grow. Even today when using Eclipse I really wish it was hosted in the cloud and I didn't have to deal with all its deployment headaches. Firefox based interfaces are pretty impressive these days. Why not?
Adam views their stack as:
1. Developer Tools
2. Application Management
3. Cluster Management
4. Elastic Compute Cloud
At the top level developers see a control panel that lets them edit code, deploy code, interact with the database, see logs, and so on. Your website is live from the first moment you start writing code. It's a powerful feeling to write normal code, see it run immediately, and know it will scale without further effort on your part. Now, will you be able toss your Facebook app into the Heroku engine and immediately handle a deluge of 500 million hits a month? It will be interesting to see how far a generic scaling model can go without special tweaking by a certified scaling professional. Elastra has the same sort of issue.
Underneath Heroku makes sure all the software components work together in Lennon-McCartney style harmony. They take care (or will take care of) starting and stopping VMs, deploying to those VMs, billing, load balancing, scaling, storage, upgrades, failover, etc. The dynamic nature of Ruby and the development and deployment infrastructure of Rails is what makes this type of hosting possible. You don't have to worry about builds. There's a great infrastructure for installing packages and plugins. And the big hard one of database upgrades is tackled with the new migrations feature.
A major issue in the Rails world is versioning. Given the precambrian explosion of Rails tools, how does Heroku make sure all the various versions of everything work together? Heroku sees this as their big value add. They are in charge of making sure everything works together. We see a lot companies on the web taking on the role of curator (, , ). A curator is a guardian or an overseer. Of curators Steve Rubel says: They acquire pieces that fit within the tone, direction and - above all - the purpose of the institution. They travel the corners of the world looking for "finds." Then, once located, clean them up and make sure they are presentable and offer the patron a high quality experience. That's the role Heroku will play for their deployable Rails environment.
With great automated power comes great restrictions. And great opportunity. Curating has a cost for developers: flexibility. The database they support is Postgres. Out of luck if you wan't MySQL. Want a different Ruby version or Rails version? Not if they don't support it. Want memcache? You just can't add it yourself. One forum poster wanted, for example, to use the command line version of ImageMagick but was told it wasn't installed and use RMagick instead. Not the end of the world. And this sort of curating has to be done to keep a happy and healthy environment running, but it is something to be aware of.
The upside of curation is stuff will work. And we all know how hard it can be to get stuff to work. When I see an EC2 AMI that already has most of what I need my heart goes pitter patter over the headaches I'll save because someone already did the heavy curation for me. A lot of the value in services like rPath offers, for example, is in curation. rPath helps you build images that work, that can be deployed automatically, and can be easily upgraded. It can take a big load off your shoulders.
There's a lot of competition for Heroku. Mosso has a hosting system that can do much of what Heroku wants to do. It can automatically scale up at the webserver, data, and storage tiers. It supports a variery of frameworks, including Rails. And Mosso also says all you have to do is load and go.
3Tera is another competitor. As one user said: It lets you visually (through a web ui) create "applications" based on "appliances". There is a standard portfolio of prebuilt applications (SugarCRM, etc.) and templates for LAMP, etc. So, we build our application by taking a firewall appliance, a CentOS appliance, a gateway, a MySql appliance, glue them together, customize them, and then create our own template. You can specify down to the appliance level, the amount of cpu, memory, disk, and bandwidth each are assigned which let's you scale up your capacity simply by tweaking values through the UI. We can now deploy our Rails/Java hosted offering for new customers in about 20 minutes on our grid. AppLogic has automatic failover so that if anything goes wrong, it reploys your application to a new node in your grid and restarts it. It's not as cheap as EC2, but much more powerful. True, 3Tera won't help with your application directly, but most of the hard bits are handled.
RightScale is another company that combines curation along with load balancing, scaling, failover, and system management.
What differentiates Heroku is their web based IDE that allows you to focus solely on the application and ignore the details. Though now that they have a command line based interface as well, it's not as clear how they will differentiate themselves from other offerings.
The hosting model has a possible downside if you want to do something other than straight web hosting. Let's say you want your system to insert commercials into podcasts. That sort of large scale batch logic doesn't cleanly fit into the hosting model. A separate service accessed via something like a REST interface needs to be created. Possibly double the work. Mosso suffers from this same concern. But maybe leaving the web front end to Heroku is exactly what you want to do. That would leave you to concentrate on the back end service without worrying about the web tier. That's a good approach too.
Heroku is just getting started so everything isn't in place yet. They've been working on how to scale their own infrastructure. Next is working on scaling user applications beyond starting and stopping mongrels based on load. They aren't doing any vertical scaling of the database yet. They plan on memcaching reads, implementing read-only slaves via Slony, and using the automatic partitioning features built into Postgres 8.3. The idea is to start a little smaller with them now and grow as they grow. By the time you need to scale bigger they should have the infrastructure in place.
One concern is that pricing isn't nailed down yet, but my gut says it will be fair. It's not clear how you will transfer an existing database over, especially from a non-Postgres database. And if you use the web IDE I wonder how you will normal project stuff like continuous integration, upgrades, branching, release tracking, and bug tracking? Certainly a lot of work to do and a lot of details to work out, but I am sure it's nothing they can't handle.