How do I enable custom domains for my users?
Your issue can be solved with URL rewrite and HTTP Header manipulation or reverse-proxy.
- For apache http server: use ProxyPassReverse directive
The directive ProxyPassReverse lets Apache adjust the URL in the Location header on HTTP redirect responses. For instance this is essential when Apache is used as a reverse proxy to avoid by-passing the reverse proxy because of HTTP redirects on the backend servers which stay behind the reverse proxy.
Suppose the local server has address http://wibble.org/; then
ProxyPass /mirror/foo/ http://foo.com/
ProxyPassReverse /mirror/foo/ http://foo.com/will not only cause a local request for the http://wibble.org/mirror/foo/bar to be internally converted into a proxy request to http://foo.com/bar (the functionality ProxyPass provides here). It also takes care of redirects the server foo.com sends: when http://foo.com/bar is redirected by him to http://foo.com/quux Apache adjusts this to http://wibble.org/mirror/foo/quux before forwarding the HTTP redirect response to the client.
- For MS(R) IIS use Re-Write Module:
Easily replace Web application URLs to produce user and search engine >friendly results. URL Rewrite permits Web administrators to easily replace the URLs >generated by a Web application in the response HTML with a more user friendly and search engine friendly equivalent. Links can be modified in the HTML markup generated by a Web application behind a reverse proxy. URL Rewrite makes things easier for outbound response content and headers rewriting with outbound rewrite rules that work with HTTP request and response headers and with IIS server variables.
Additionaly, you must make sure that exampledavid(dot)com is setup with DNS provider to pass all requests to example.com.
DNS Record Sample:
NAME TYPE VALUE
--------------------------------------------------
exampleXYZ.com. CNAME example.com.
example.com. A 192.0.2.23
Ref:
https://en.wikipedia.org/wiki/CNAME_record
http://www.akadia.com/services/apache_redirect.html
http://httpd.apache.org/docs/2.2/mod/mod_proxy.html
http://www.iis.net/downloads/microsoft/url-rewrite
You can easily enable this by telling your clients to configure a CNAME to point to your domain.
So if your server is located at www.example.com you tell 'david' to configure www.exampledavid.com to have a CNAME record pointing to www.example.com
At the server end you would have a configuration that detected the domain that was being requested and redirected and served the appropriate content to 'david'
If your clients want to use the naked domain i.e. exampledavid.com to your servers, you would need to provide them with an IP address, however before doing this you would need to be sure that your IP address wasn't going to change, and probably have a contract with whoever supplies it to ensure that.
I see decent answers but no one here is giving the full picture.
If your customers just CNAME to your domain or create the A record to your IP and you don't handle TLS termination for these custom domains, your app will not support HTTPS, and without it, your app won't work in modern browsers on these custom domains.
You need to set up a TLS termination reverse proxy in front of your webserver. This proxy can be run on a separate machine but you can run it on the same machine as the webserver.
CNAME vs A record
If your customers want to have your app on their subdomain, e.g. app.customer.com they can create a CNAME app.customer.com pointing to your proxy.
If they want to have your app on their root domain, e.g. customer.com then they'll have to create an A record on customer.com pointing to your proxy's IP. Make sure this IP doesn't change, ever!
How to handle TLS termination?
To make TLS termination work, you'll have to issue TLS certificates for these custom domains. You can use Let's Encrypt for that. Your proxy will see the Host header of the incoming request, e.g. app.customer1.com or customer2.com etc., and then it will decide which TLS certificate to use by checking the SNI.
The proxy can be set up to automatically issue and renew certificates for these custom domains. On the first request from a new custom domain, the proxy will see it doesn't have the appropriate certificate. It will ask Let's Encrypt for a new certificate. Let's Encrypt will first issue a challenge to see if you manage the domain, and since the customer already created a CNAME or A record pointing to your proxy, that tells Let's Encrypt you indeed manage the domain, and it will let you issue a certificate for it.
To issue and renew certificates automatically, I'd recommend using Caddyserver, greenlock.js, OpenResty (Nginx).
tl;dr on what happens here; Caddyserver listens on 443 and 80, it receives requests, issues, and renews certificates automatically, proxies traffic to your backend.
How to handle it on my backend
Your proxy is terminating TLS and proxying requests to your backend. However, your backend doesn't know who is the original customer behind the request. This is why you need to tell your proxy to include additional headers in proxied requests to identify the customer. Just add X-Serve-For: app.customer.com or X-Serve-For: customer2.com or whatever the Host header is of the original request.
Now when you receive the proxied request on the backend, you can read this custom header and you know who is the customer behind the request. You can implement your logic based on that, show data belonging to this customer, etc.
More
Put a load balancer in front of your fleet of proxies for higher availability. You'll also have to use distributed storage for certificates and Let's Encrypt challenges. Use AWS ECS or EBS for automated recovery if something fails, otherwise, you may be waking up in the middle of the night restarting machines, or your proxy manually.
If you need more detail you can DM me on Twitter @dragocrnjac