[MidoNet] Data stored in Cassandra / DHCP IP addresses

Giuseppe (Pino) de Candia gdecandia at midokura.com
Tue Nov 11 08:50:41 UTC 2014


On Tue, Nov 11, 2014 at 8:37 AM, Jan Hilberath <jan at midokura.com> wrote:

> Hi All,
>
> Is there any document (or can anyone provide the info here) about what
> data is being stored in Cassandra?
>

Hi Jan,

I can't answer regarding where this is documented. However, the Cassandra
question has come up before and there may be a ticket open about it.

Cassandra is used only to store per-flow data (connection-tracking, dynamic
NAT and LB decisions). Since v1.6, this data is also passed directly
between MN Agents that need it (ingress hosts of forward and return flows)
at flow creation time and stored locally; the data in Cassandra is only
used on node reboot or VM migration (cases when the Agent loses or doesn't
have local flow state).


>
> For example, the IP address a VM receives via DHCP, where is that stored?
>

This is stored in ZooKeeper in the DHCPSubnet object (and MacIP
sub-object). This object gets created inside MN when the Neutron Subnet is
created. It's populated with MacIP objects each time a new Neutron Network
Port is created (and therefore and IP and MAC assigned by Neutron to the
port).


>
> My understanding is that a VM get's the same DHCP IP address on every
> reboot (guess mapped to the MAC).


Correct.


> Assuming I clean all Cassandra data, will my VM still receive the same
> DHCP IP address?
>

As should already be clear from above, Cassandra is not involved in the
DHCP.

thanks for the questions! Please keep them coming and let's try to get all
this into the docs.

--Pino


> Thanks,
> Jan
>
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