The full DNS lowdown for your website - A practical guide focusing on Windows Azure

Ok, so what is DNS or the Domain Name System? I have always thought of it as a human friendly way of naming computers which are serving content. However, while a snappy explanation to serve up to a non technical person, it does not really get to the knob of the issue.

DNS assigns names to IP addresses, DNS is Hierarchical and DNS is a protocol.

The DNS protocol specification simply describes how the DNS records should be formatted. This means that there is no need to have a single centralised database, indeed this would be very unwise!

Each DNS record has a type. There are a number of types, but the most commonly used are A, CNAME, MX and NS.

For those who really want to dig into the full specification Microsoft have compiled the current documents for the DNS specification here. For instance if you want to know what the types really are see RFC 1034 (November 1987).


Setting up DNS for your website

So moving away from theory to real life ...I want to set up my website so that when you type the URL mysite.com into chrome it goes straight to my website.

First of all I need to buy a domain name. There are a number of providers, Ghandi and DNSSimple are considered particularly good ones.

Once I have bought a domain name I can get going and set-up some CNAME (canonical name of an Alias - see RFC 1034 :-) ) records. This is because in this first instance I am telling my domain name to simply look for the azure domain name server which will be something like myproject.azuresites.com.

Therefore my CNAME record looks like:

host	type	target
www	CNAME	myproject.azuresites.net

So when I go to www.mydomain.com I get the resource hosted at myproject.azuresites.net.

What is actually happening here is that Azure has already setup an A record pointing from myproject.azuresites.net to the virtual IP address. The virtual IP address will then resolve to any number of different boxes in their "Cloud" server farm. I imagine it is probably powered by nerd sweat =P.

DNS changes can take up to 48 hours to propagate, although personally I have never had to wait longer than half an hour. There are a few little tricks which can help to minimise any confusion:

1. Try checking a DNS tracking site e.g. whatsmydns.net 
2. If it has propagated and you are still not seeing the correct result try flushing your local DNS cache by going to the cmd prompt and typing: ipconfig/flushdns.

Incoming email

What I want to do is push all the emails sent into my domains email address into my gmail account. To do this I need to understand a little about the DNS Mail Exchanger (MX) record.

So, the MX record.

host	type	target

  @          MX             ? depends ?

The target depends on what you are trying to achieve. You need a "mailbox" which is going to track emails going to your domain. E.g. to email@mydomain.com.

The easiest way is to buy a mailbox from your domain supplier and then configure your preferred email client app (e.g. gmail, yahoo etc...) to look at their SMTP server. You can then send/receive the mail from the mailbox via SSL encrypted connection. Take a look at this page for help on setting this up. I am working on providing you an alternative solution so watch this space...!

Outgoing Email

This is actually a big subject, many organisations and individuals have got into a lot of trouble over outgoing emails form an app. Span has always been the issue. The steps put in place to reduce spam have unfortunately produced a world where people often say "Your system/ you didn't send the email :( ".... " yes I have :/"..."Have you checked your span filter? :)". 



Non-www

Generally people no longer bother with typing the full address www.mydomain.com. In fact, the average Joe, will be completely baffled as to why their browser throws back an error.

Again DNS comes to the rescue, try:

host	type	target

  @      CNAME    myproject.azuresites.net

If you use this in conjunction with the 'www' record mentioned above then your users should be able to go to www.mydomain.com or mydomain.com with the same result.... some juicy content. hmmm!

Generally you may think that one or the other domain names (non-www or with www) is the preferable URL which should be visible to "the average Joe". What you probably want is the server to immediately redirect to say mydomain.com as soon as somebody goes to www.mydomain.com in their browser.

There are a number of techniques for doing this. With an IIS or Apache web server you can use a command line file which by convention is of the file type .htaccess. Placing this file in the route directory of your code will cause the hosting OS to immediately run the file when serving a resource. You can write something like:

# Redirect www urls to non-www
RewriteEngine on
RewriteCond %{HTTP_HOST} !^mydomain\.com
RewriteRule (.*) http://mydomain.com/$1 [R=301,L]

I am using NodeJS and this has its own technique to achieve this:

// redirect for non-www
app.all('/*', function(req, res, next) {
  if (req.headers.host.match(/^www\./) !== null) {
    res.redirect(301, req.protocol + '://' + req.headers.host.replace(/^www\./, '') + req.url);
  } else {
    next();
  }
})

app.set('trust proxy', true);

Sub-domains

Again these are easy to setup as well. Simply use the * symbol in your CNAME record:
* CNAME myproject.azuresites.net

Then the request to a certain subdomain e.g. elephants.mydomain.com can be sniffed for and intercepted by your code.