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Cloud IP Port Translation


Each Cloud Server has a single network interface, and therefore a single private “real” IPv4 address (10.x.x.x). So, whilst you can map multiple Cloud IPs to one Cloud Server, all traffic comes into the same single IPv4 address. This makes hosting different web sites with different TLS/SSL certificates on the same server difficult, since the web server can’t distinguish between the different Cloud IPs.

For example, if you map two Cloud IPs to a server listening on HTTPS port 443, both Cloud IPs will serve the same site with the same certificate.

The new TLS/SSL Server Name Indication feature is designed to solve this kind of problem, but not all browsers support it (for example, Internet Explorer on Windows XP).

The Solution: Port Translation

Port Translation enables you to change the destination port of incoming connections on a particular Cloud IP. This behaviour can be used to host multiple SSL sites on a single server or load balancer.

For example, let’s assume we need to host two TLS/SSL sites on our server, one for cats.com and the other for dogs.com

We configure our Apache web server so that cats.com listens on port 443 as usual:

Listen 443

<VirtualHost *:443>
  ServerName cats.com
  SSLEngine On
  SSLCertificateFile /etc/ssl/certs/cats.crt
  SSLCertificateKeyFile /etc/ssl/private/cats.key
  DocumentRoot /home/cats/public

Then we create our first Cloud IP as normal and map it to our server:

$ brightbox cloudips create -n "cats" 

 id         status    public_ip      destination  name
 cip-360ea  unmapped               cats (cip-109-107-37-80.g...

$ brightbox cloudips map cip-360ea srv-9igaa
Mapping cip-360ea to interface int-zylp1 on srv-9igaa

 id         status  public_ip      destination  name                   
 cip-360ea  mapped  srv-9igaa    cats (cip-109-107-37-80.gb1...

If we update the dns for cats.com to point at this IP then the cats.com site is now live.

Now we configure Apache so that dogs.com listens on a different port, let’s use 2443

Listen 2443

<VirtualHost *:2443>
  ServerName dogs.com
  SSLEngine On
  SSLCertificateFile /etc/ssl/certs/dogs.crt
  SSLCertificateKeyFile /etc/ssl/private/dogs.key
  DocumentRoot /home/dogs/public

Now we create a second Cloud IP, but this time we specify a port translation to translate tcp port 443 to 2443:

$ brightbox cloudips create -n "dogs" --port-translators=443:2443:tcp

 id         status    public_ip       destination  name
 cip-dnx8z  unmapped               dogs (cip-109-107-37-228...

And then map it to the server as normal:

$ brightbox cloudips map cip-dnx8z srv-9igaa
Mapping cip-dnx8z to interface int-zylp1 on srv-9igaa

 id         status  public_ip       destination  name                  
 cip-dnx8z  mapped  srv-9igaa    dogs (cip-109-107-37-228.g...

Now if we update the DNS for dogs.com to point at this second IP, then dogs.com is live too!

You can view the port translators for a particular Cloud IP using the brightbox cloudips show command:

$ brightbox cloudips show cip-dnx8z

              id: cip-dnx8z
            name: dogs
          status: mapped
     reverse_dns: cip-109-107-37-228.gb1.brightbox.com
     destination: srv-9igaa
    interface_id: int-zylp1
port_translators: 443:2443:tcp

You can define multiple translators per Cloud IP by comma separating them, and you can, of course, change or remove them at any time using the brightbox cloudips update command.

You can translate UDP ports as well as TCP ports, so you can run things like multiple DNS services on the same server too.

You can learn more about Cloud IPs in the Cloud IP guide or in the reference page (which also has more details about port translation).

Last updated: 26 Apr 2021 at 16:04 UTC

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