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I am doing research to support the spec for TripleO deployment on
routed networks [1]. I would like some input on how to represent
multiple subnet ranges for the provisioning network in undercloud.conf.

The Ironic Inspector dnsmasq service is currently configured using the
puppet-ironic module, and the range of IP addresses is taken directly
from undercloud.conf. For example, here is the .erb which configures
/etc/ironic-inspector/dnsmasq.conf if using TFTP [2]:

###### inspector_dnsmasq_tftp.erb ######
port=0
interface=<%= @dnsmasq_interface %>
bind-interfaces
dhcp-range=<%= @dnsmasq_ip_range %>,29
dhcp-boot=pxelinux.0,localhost.localdomain,<%= @dnsmasq_local_ip %>
dhcp-sequential-ip
############

Since there is only one dnsmasq_ip_range, only a single subnet is
served via DHCP. What I would like to do is extend the undercloud.conf
to support multiple IP ranges, and I'm looking for input on the best
way to represent the data.

I am not sure if we can be fully backwards-compatible here. My gut
feeling is no, unless we leave the existing parameters as-is and add
something like an "additional_inspection_ipranges" parameter. The data
that will need to be represented for each subnet is:

* Network subnet
* Start and end of inspection IP range
* Subnet mask (could be determined by parsing cidr, like 172.20.1.0/24)
* Gateway router for the subnet

We could potentially represent this data as a JSON, or as a list of
strings. Here are some potential examples:

JSON:
additional_inspection_ipranges = [
  {
    "subnet": "172.20.1.0/24",
    "start": "172.20.1.100",
    "end": "172.20.1.120",
    "gateway": "172.20.1.254"
  },
  {
    "subnet": "172.20.2.0/24",
    "start": "172.20.2.100",
    "end": "172.20.2.120",
    "gateway": "172.20.2.254"
  }
]

String:
additional_inspection_ipranges =
"172.20.1.0,172.20.1.100,172.20.1.120,255.255.255.0,172.20.1.254;172.20.2.0,172.20.2.100,172.20.2.120,255.255.255.0,172.20.2.254"

Either of these might get unwieldy depending on the number of networks.
Perhaps we could have a repeating parameter? Something like this:

additional_inspection_iprange =
"172.20.1.0,172.20.1.100,172.20.1.120,255.255.255.0,172.20.1.254"
additional_inspection_iprange =
"172.20.2.0,172.20.2.100,172.20.2.120,255.255.255.0,172.20.2.254"

I would like some feedback about how to represent this data in a way
that it can be easily parsed by Puppet, while remaining readable. Any
suggestions would be very much appreciated.

[1] - https://review.openstack.org/#/c/377088
[2] -
https://github.com/openstack/puppet-ironic/blob/master/templates/inspector_dnsmasq_tftp.erb
-- 
Dan Sneddon         |  Senior Principal OpenStack Engineer
dsneddon at redhat.com |  redhat.com/openstack
dsneddon:irc        |  @dxs:twitter