Open Stack

Hi all,

I  was working in an openstack project to build a small to medium level
public cloud on the top of openstack. We are researching lot more about
scalable large openstack deployments and planning our design accordingly.
Initially we will be having 50+ compute nodes and planning to grow up to
200 compute nodes in an year by migrating the existing clients to new
platform.

I have many concerns about the scaling and right choices , since openstack
is offering lot of choices and flexibility, especially in networking
side.Our major challenge was choosing between simplicity and performance
offered by Linux bridge and features and DVR offered by OVS.  We decided to
go with OVS, though some were suggesting like OVS is slow in large
deployments. But the distributed L3 agents and bandwidth offered by DVR
inclined us towards OVS. Is it a better decision?

But one of the major drawback we are seeing with DVR is the public IP
consumption. If we have 100 clients and 1 VM per client , eventually there
will be 100 tenants and 100 routers. Since its a public cloud, we have to
offer public IP for each VM. In DVR mode, fip name space in compute will be
consuming one public IP and if 100 VMs are running among 20 computes, then
total 20 public IPs will be used among computes. And a router SNAT name
space will be created for each tenant router(Total 100)  and each of it
will be consuming 1 public  IP and so total 100 public IPs will be consumed
by central SNAT name spaces. So total 100 + 20 = 120 public IPs will be
used by openstack components and  100 will be used as floating IPs (1:1
NAT) by VMs. So we need 220 public IPs for providing dedicated public IPs
for 100 VMs !! Anything wrong with our calculation?

>From our point of  view 120 IPs used by openstack components in our case
(providing 1:1 NAT for every VM) is wastage of IPs and no any role in
network traffic. Centrallized SNAT is useful , if the client is opting for
VPC like in AWS and he is not attaching floating IPs to all instances in
his VPC.

So is there any option while creating DVR router to avoid creating central
SNAT name space in controller node ? So that we can save 100 public IPs in
the above scenario.
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