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Why does OpenStack provider network setup require two compute nodes?

asked 2016-05-16 04:29:34 -0600

Muff gravatar image

updated 2016-05-16 04:30:28 -0600


As stated in the title, why does OpenStack provider network setup require two compute nodes? Here: ( it is stated "At least two compute nodes" but I cannot understand why?

Why is not one compute node enough?


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answered 2016-05-16 05:48:20 -0600

dbaxps gravatar image

updated 2016-05-16 10:30:26 -0600

UPDATE MSK 17:50 05/16/2016

Relaying on already existing physical network infrastructure. They involve provider network (vlan) for creating networks connecting  Compute Nodes and Controller/Network Node. Thus this networks has IP address and MASK what requires  Router/Switch blocks like on pictures at mentioned link.Even though, if East/West traffic is not your major concern. One Compute Node might be enough.

The core target is :-

Provider networks lack the concept of fixed and floating IP addresses because they only handle layer-2 connectivity for instances.

So,they avoid traditional for Neutron L3 routing
Snapshots bellow from mentioned link is a fair for suggested design

image description

image description

I might be missing something , but
is silently skipping the problem with cloud VMs requests to Nova Metadata Server.

I  am talking about "isolated_metadata=True" in dhcp_agent.ini.

My original answer is irrelevant to question. It presumes Neutron L3 routing in both cases. However, all fg-xxxx (Link 1) from fip-namespaces and qg-xxxx outgoing interfaces from qrouter-namespaces (Link 2) would be attached to br-int. Un-bridged external routing would come into play due to External network providers involvement.

I believe that 2 Compute Nodes in case of DVR cluster are needed to verify that East-West traffic will avoid routing via Network or Controller/Network Node , otherwise see sample bellow, which might be tested on Two Node DVR cluster with External network flat provider (Controller/Network && Compute).
Running DVR with Two external networks via flat network provider on CentOS 7.2 RDO Liberty
Another sample with External vlan network provider, which might be tested on Two Node Cluster Controller/Network&&Compute.
RDO Mitaka & Several External Networks VLAN Provider Setup

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Thanks for your answer. My major concern is not East/West traffic but rather North/South. So if I understand it correctly, for North/South traffic one compute node is enough?

Muff gravatar imageMuff ( 2016-05-17 04:24:49 -0600 )edit

Take a look at picture (1) 1xController/Network + 1xCompute.

dbaxps gravatar imagedbaxps ( 2016-05-17 05:34:49 -0600 )edit

You are correct. I was insufficient in my statement, I meant to include the cloud controller, but I never wrote it down. Thanks a lot for the answer.

Muff gravatar imageMuff ( 2016-05-17 05:55:34 -0600 )edit

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Asked: 2016-05-16 04:29:34 -0600

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Last updated: May 16 '16