- High Scalability

I first heard an enthusiastic endorsement of Squarespace streaming from the ubiquitous Leo Laporte on one of his many Twit Live shows. Squarespace as a fully hosted, completely managed environment for creating and maintaining a website, blog or portfolio was of interest to me because they promise scalability and this site doesn't have enough of that. But sadly, since they don't offer a link preserving Drupal import our relationship was not meant to be.

When a fine reader of High Scalability, Brian Egge, (and all my readers are thrifty, brave, and strong) asked me how Squarespace scaled I said I didn't know, but I would try and find out. I emailed Squarespace a few questions and founder Anthony Casalena and Director of Technical Operations Rolando Berrios were kind enough to reply in some detail. The questions were both from Brian and myself. Answers can be found below.

Two things struck me most about Squarespace's approach:

They based their system on a memory grid, in this case Oracle Coherence. I'm not aware of too many customer facing systems that have moved to a grid as the backbone of their scalability strategy. It's good to see a successful system visible out in the wild.

They use a sort of Private Cloud internally. Everything is highly automated and easy to expand. They scale by adding additional resources like CPUs and disks and the system just adapts without a lot of human fussing involved. Now that's scaling with gas.

Learn more about how Squarespace has learned how to scale to tens of thousands of customers, hundreds of thousands of signups, and serve hundreds of millions of hits per month.

Site: http://www.squarespace.com

The Stats

Tens of thousands of customers.

Hundreds of thousands of signups.

Serves hundreds of millions of hits per month.

Platform

Java - well supported and an advanced language to work in, and the components out there (Apache Foundation, etc.) are second to none.

Tomcat - the stability of the server is extremely impressive.

Grid - Oracle Coherence for the re-balancing and caching layers.

Storage - Isilon Cluster. This allows them to treat their storage like another "grid" as the storage pool is easily scaled by adding more diskspace.

Monetiziation Strategy - charge money. No free customers. Pricing starts at $8/month.

Uptime - 99.98%

Hosting - Peer1, they do not yet operate in multiple datacenters.

Competitors - TypePad and WordPress

Hardware - they don't use "commodity nodes" or low cost hardware units. These end up costing more in the long run as datacenter power is extremely expensive.

Cacti - a cacti instance is used to graph statistical data which helps see trends over time, predict when a hardware upgrade is necessary, and troubleshoot any problems that do show up.

Lessons Learned

Cache as much as you can and load balance requests intelligently across a cluster.

Use an infrastructure that scales automatically merely by adding more resources (CPU, disk).

Build a scalable design up front. Make scaling easy by designing the application and infrastructure with scaling in mind.

Build a hands-off capable maintenance system. Automate processes. Make them as simple as possible. Monitor programatically so people don't have to.

Release code early and often. Running on the latest code means problems can be detected quickly when the problem are small.

Keep things simple. Apply simplicity to every part of your infrastructure, including both your software and those of your outside vendors. Examples of this are: Grid for the application infrastructure, Isilon cluster for storage, automation, creating their own tools.

Use as few technologies as possible by selecting or building simple, powerful and robust tools.

Don't be afraid to implement your own code to ensure simplicity. Build or buy is a huge balancing act.

Don't be afraid to spend money on technology that helps you get where you need to go. It can save you months and months of headaches that would have prevented you from working on core functionality.

Interview Questions and Responses

They say they run on a grid. I'd be interested to know if they built their own grid?

Partially. We rely on Oracle's Coherence product for the re-balancing
and caching layers of our system -- which we consider a real workhorse
for the "grid" aspects of the system. Each node in our infrastructure
can handle a hit for any single site on the system. This means that in order to increase capacity, we just increase node count. No site is handled by a single node.

2. How much traffic they can really handle?

We've had several customer sites on the front page of Digg on multiple
occasions, and didn't notice any performance degradation for any of our
sites. In fact, we didn't even realize the surge happened until we reviewed our traffic reports a few hours later. For 99% of sites out there, Squarespace is going to be sufficient. Even larger sites with millions of inbound hits per day are servable, as the bulk of the traffic serving on those sites is in the media being served.

3. How do they scale up, and allow for certain sites to become quite busy?

We've tried to make scaling easy, and the application and infrastructure
have been designed with scaling in mind. Because of this, we're luckily not
in a situation where we need to keep getting bigger and beefier hardware to handle more and more traffic -- we try to scale out by supplementing the
grid. Since we try to cache as much as we can and every server
participates in handling requests for every site, it's generally just a
matter of adding another node to the environment.

We try to apply this simplicity to every part of our infrastructure, both
with our own software and when deciding on purchases from outside vendors. For instance, we just increased the amount of available storage another few terabytes by adding another node to our Isilon cluster.

4. Are there any stats you can share about how many customers, how many users, how many requests served, how many servers, how much disk, how fast, how reliable?

We, unfortunately, can't share these numbers as we're a private company
-- but we can say we have tens of thousands of customers, hundreds
of thousands of signups, and serve hundreds of millions of hits per
month. The server types and disk configurations (RAID, etc) are a bit
irrelevant, as the clustering we implement provides redundancy -- not
anything implemented into a particular single machine. Nothing in
hardware is too particular to our setup. I will say we don't purchase
"commodity nodes" or other low cost hardware units, as we find these
end up costing more in the long run as datacenter power is extremely
expensive.

5. What technology stack are you using and why did you make the choices you made?

We currently use Java along with Tomcat as our web server. After
trying a few other solutions, we really appreciated the ability to use
as few technologies as possible, and have those always remain things
that are understandable for us. Java is an incredibly well supported
and advanced language to work in, and the components out there (Apache
Foundation, etc.) are second to none. As for Tomcat, the stability of
the server is extremely impressive. We've implemented our own
controller mechanisms on top of Tomcat (instead of going with some
other library) in order to ensure extreme simplicity.

6. How are you handling...

Multi-tenancy?

As mentioned above, every web node handles traffic for all sites, so a
customer doesn't have to worry about an underpowered server unable to handle their traffic, or a node going down.

Backups?

Backups are obviously important to us, and we have several copies of user
and server data stored in multiple locations. We gather backups with a
combination of various home-grown scripts customized for our environment.

Failover? Monitoring?

Since this company originally was solely maintained by Anthony when he
first started it, things needed to be as simple and automated as possible.
This includes failover and monitoring. Our monitoring systems check every
aspect of our environment we can think of several times a minute, and can
restart obviously dead services, or alert us if it's something an
actual person needs to handle.

Additionally, we've set up a cacti instance to graph as much statistical
data as we can pull out of our servers, so we can see trends over time.
This allows us to easily predict when a hardware upgrade is necessary. It also helps us troubleshoot any problems that do show up.

Operations? Releases? Upgrades? Add new hardware?

With our customer base constantly growing, it's getting tough to manage our systems and still keep our workload under control. There are some projects on the road map to move to a much more hands-off maintenance of our environment, including automatic code deployments and system software upgrades. Most operations can be done without taking the grid offline.

Multiple data centers?

We do not have multiple data centers, but have some plans in the works to
roll one out within the next year.

Development?

This is a really broad question, so it's a bit hard to succinctly
answer. One thing (amongst many) that has consistently served us very
well is trying to ensure our development environment is always
releasable into production. By ensuring we're always out there with
our latest code, we can usually detect problems very rapidly, and
as a result, those problems are generally extremely small. Everyone on our development team tends to be responsible for wide, sweeping aspects of the system -- which gives them a lot of flexibility to determine how
their components should work as a whole. It's incredibly important
that everything fits seamlessly together in the end, so we spend a lot
of time iterating on things that other groups might consider finished.

Support?

Support is something we take extremely seriously. As we've grown from
the ground up without an external investor, most of our team members
are versed in support, and understand how critical this component is.
Our support staff is completely hired from our community, and is
incredibly passionate about their jobs. We try and get every single
customer support inquiry answered within 15 minutes or less, and have all sorts of metrics related to our goals here.

7. What have you done that's really cool that you think other people could learn from?

We spend a lot of time internally writing scripts and other
applications that simply run our business. For instance, our
persistence layer configuration files are generated by applications
we've written that read our database model directly from the database.
We develop a lot of these programs, and a lot of "standard naming"--this, again, means that we can move very rapidly as we have less monotonous tasks and searching to think about.

While this sort of thing is appropriate for small tasks, for the big
ones, we also aren't afraid to spend money on well developed
technology. Some of our choices for load balancing and storage are
very costly, but end up saving us months and months of time in the
long haul, as we've avoided having to "put out fires" generated by
untested home grown solutions. It's a huge balancing act.

The End

Often the best way to judge a product is to peruse the developer forums. It's these people who know what's really happening. And when I look I see an almost complete absence of threads about performance, scalability, or reliability problems. Take a look at other CMSs and you'll see a completely different tenor of questions. That says something good about the strength of their scalability strategy.

I'd really like to thank Squarespace for taking the time and making the effort to share they've learned with the larger community. It's an effort we all benefit from. If you would also like to share your knowledge and wisdom with the world please get in touch and let's get started!

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