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To WWW or not WWW

Matt Biilmann posted this on February 28, 2017

Note, if you use Netlify’s built-in DNS service, there’s absolutely no difference between using www or not - if you’re using an external DNS provider, then read on.

Your DNS Setup can have a great effect on performance and DDoS resilience. Our site for Netlify is hosted on www.netlify.com, rather than netlify.com

We call netlify.com the “apex” domain or “root” domain.

Some might think that this is merely a cosmetic difference and make whole websites arguing against the www prefix. However, dropping www from your main site domain can have dire consequences because of how DNS records work.

DNS Records

DNS is the internet-wide phonebook that tells browsers (and any other connected system), how to resolve a specific domain name to an IP address of a server they can open a connection to.

For websites, there are 2 kinds of records relevant to hosting a website with Netlify:

  • A Record

An A record returns an IPv4 address of a server

  • CNAME Record

Returns another domain name that the browser should lookup instead

When you configure a custom domain to point to a Netlify site, we always recommend that you use a CNAME record pointing at <yoursite>.netlify.com (where <yoursite> depends on the name of your Netlify site).

Lets say you’ve configured www.example.com to return a CNAME pointing at example.netlify.com.

When a user visits your site, her browser will lookup the DNS record for www.example.com, it will receive a CNAME telling it to look up example.netlify.com instead. When it looks up example.netlify.com, it connects to our advanced traffic director, that returns an A record with an IP address of the server from our pool of currently available CDN nodes that’s geographically closest to the end user.

The cool thing about this is that if our system has detected that our main load balancer is currently being hit by a large DDoS attack and is slow or unresponsive, we’ll simply route around that on the DNS level. Since we cache content at our edge nodes around the world, end users also experience extremely fast page load times because of this.

The Trouble with Apex Domains

This is all great, but lets say you’d like your site to live directly at example.com instead of www.example.com.

You might think you could simply configure a CNAME record for the apex domain and be done with it, but you shouldn’t!  This could severely break other things for you.

The problem with CNAME records is that the DNS specification doesn’t allow any other DNS records on a name that has a CNAME record set.

When you have a specific name for your website like www or app or any other subdomain, that’s not a problem. For the apex domain, however, this is different.

If you want to be able to receive email on your domain, you’ll need to set MX records at the apex domain. With a CNAME, no other records can be set.

Want to validate your domain for something like Google’s webmaster tools? Or perhaps you’d like to use the SPF system to help verify your email sending hosts? Now you have to add a TXT record to the apex domain. If you already have a CNAME, again, that’s not allowed.

A records, Outages and DDoS Attacks

Even if your site lives at www.example.com instead of example.com, you’ll still want a way to point example.com at our servers so we can serve a 301 redirect from example.com to www.example.com when a user visits the apex domain.

Since setting a CNAME record on the apex domain will break email and wreck havoc on TXT records, the only remaining option is currently an A record (in the future AAAA records will be an option as well).

Since an A record needs to point to a raw IP address, we publish the IP address of our main load balancer for this purpose.

The problem is that an A record doesn’t let us insert any traffic direction between the end user’s DNS lookup and our infrastructure. So we have no way of routing users to the closest CDN node, and if our main load balancer for some reason goes unresponsive, we have no way of routing traffic coming directly from A records around this.

Because of this we strongly recommend that you always host your main site or app on www or any other subdomain (app.example.com is perfectly fine as well). This way you can use a CNAME record for the canonical site URL. You’ll take full advantage of our globally distributed infrastructure and we can automatically route around any localized outage.

The root domain at example.com will still work, but will simply redirect to www.example.com. With Netlify this redirect happens straight on the CDN edge nodes and is extremely fast.

CNAME Flattening, ANAME or ALIAS Records

However, there is an available alternative!  Some DNS hosts have paid attention to the no-www crowd and implemented a workaround.

NS1 offers ALIAS records, DNS Made Easy have support for ANAME records and Cloudflare supports CNAME Flattening.

None of these are part of the DNS spec, but are all different workarounds to solve the limitations of CNAMEs.

When you set an ALIAS record for example.com pointing at example.netlify.com, then NS1 will do the CNAME look up itself, instead of delegating that to the browser.

Normally the browser would get a CNAME record, follow that to example.netlify.com, and then receive the IP address of the closest available server.

With an ALIAS record, instead NS1 itself checks example.netlify.com and returns an A record with an IP address directly to the browser.

There are two benefits:

  • You essentially get the benefit of a CNAME for your apex domain

We can still route around outages and do some geographic traffic direction

  • End users save an extra DNS lookup

Instead of first looking up the CNAME record, and then looking up the final IP, the browser gets an IP straight away.

However, there’s also an important drawback:

  • The precision of the geographic lookups that Netlify does might suffer

We now do our lookup based on the IP of the DNS server rather than the IP of the end user, which can lead to inaccuracies based on the lack of granularity of those servers. Plus, for performance reasons, DNS servers can do some caching of IP lookups that can lower the precision. In general these drawbacks are not severe or universal in their effects, so given the choice, the enhanced record should be used instead of the A record. But, feel free to ask support to take a look at your setup to advise.

The ideal setup

The ideal setup that we recommend is to use www or any other subdomain as the canonical domain for your website, but still use a DNS host that supports some form of CNAME on the apex domain.  Our own DNS hosting does this, for instance (and handles configuration automatically for you too!)

This way you’ll get the full benefit of our global DNS traffic direction on your main site, and we can also route around outages when doing the redirect from apex domain to www domain.

Hope this was informative!

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