[CentOS] Configuring source-specific routing

Thu May 2 13:14:29 UTC 2013
Michael Mol <mikemol at gmail.com>

On 05/02/2013 08:57 AM, Les Mikesell wrote:
> On Wed, May 1, 2013 at 4:52 PM, Michael Mol <mikemol at gmail.com> wrote:
>> Intent is to maintain the old, slow (but has an SLA) connection as a
>> fallback, and migrate services to the new connection piecemeal.
>> Meanwhile, the same DNS server on the new connection can be, e.g. "ns3".
>> The same mailserver can have a new MX on the new connection...likely
>> prioritized to it.
> Note that there are more straightforward ways to do this.   One is to
> pretend you are big enough to have a distributed server farm and
> actually have independent servers at the other IPs, even if they are
> VMs.  This is fairly easy for mostly-static or database-driven web
> sites, fairly difficult for apllications that are more statefull but
> perhaps possible with a common NFS backend.   Another is to have
> application-level proxies or load balancers like haproxy, nginx,
> apache configured as a reverse-proxy, or even port forwarding with an
> xinetd 'redirect' configuration.  This loses the source ip from the
> application logs, although the http proxys have an option to pass
> them.   Similarly you could use iptables to source-nat on the
> receiving side and forward to a backend server.    These all have some
> disadvantages, but with separate hosts each having one default gateway
> to the internet and static routes for your own local ranges you have a
> lot less black magic involved.

Actually, this is all stuff (well, except for haproxy) we have
implemented. 80-90% of my servers don't even need (and, ultimately,
won't have) public IP addresses. (And I still won't need NAT, thank god.)

Internally, I'm not far from having things set up as a fluid private
cloud with scaleable services.

Ultimately, for this to work cleanly, anything which requires a public
IP (be it a raw authoritative DNS server or a load balancer) will
require an IP on both public subnets.

The only blocker right now is getting CentOS to do source-policy routing

-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 555 bytes
Desc: OpenPGP digital signature
URL: <http://lists.centos.org/pipermail/centos/attachments/20130502/16f9aa19/attachment-0005.sig>