Question: I'm confused with this line in the Heroku docs (<https://devcenter.heroku.com/articles/ssl-certificate>)

> 
> You must enter a subdomain in the “Host Name” field. Leaving it blank will generate a root-domain certificate which is not compatible with Heroku’s SSL endpoint. 
> 
> 
> 

What I want is <https://foo.com> and <https://www.foo.com> to work.

So what do I need to fill in this field to get a SSL certificate that will help me achieve the above?

![DNSimple SSL Certificate Purchase](https://i.stack.imgur.com/ww97y.png)

The rest of the steps (setting CNAME to Heroku's SSL endpoint, adding an ALIAS to redirect the root domain etc) are clear to me. I'm just stuck on this step, should it be blank or 'www' or something else?

Answer: 
If you want your certificate to be valid for the rood domain AND the www hostname, then you should use the `www.example.com` version.

You can also purchase a wildcard, but unless you need to support any extra subdomain, the cost is not worth in this case.

More details are available in the support page [Selecting the Certificate Hostname](http://support.dnsimple.com/questions/48899-Selecting-the-Certificate-Hostname).
You should fill in www. 

www is just a subdomain so that will solve your www.foo.com problem but you will have to redirect the naked domain <https://foo.com> to the www one though.