IPAM Internal DB table / update

cody_c · May 28, 2020, 6:21pm

During baremetal provisioning, we need to add a second IP to a second interface on a box. I’ve gotten this to work by first running the discovery build, then getting the host info, the ID of the second interface and assigning an IP by updating that interface with a subnet ID, which then grabs the IP all great like. Problem is for that subnet (set to DHCP for the IPAM), foreman can’t actually reach that subnet so I’m getting duplicated IP assignments. From reading various bits, I guess this can happen as the DHCP server has no way to ping an IP to ensure it’s not used.

I also, on host creation, don’t see any records showing up in the DHCP lease files. So I’m thinking I can just move to Internal DB or Random DB for the IPAM for this one subnet.

To get to my question, I’m wondering where in the database these IPs are stored, what table and format as taking a general look at things I couldn’t guess it.

Also how are these IP values updated, is it only on creation, or on puppet fact update as well?

How does setting to Random DB or Internal DB determine what the next IP to use should be?

If the database is lost will all the assigned IPs for this subnet also be lost, or can it be re-updated from puppet runs / facts that get loaded in as hosts re-run puppet?

Oh and how are the IP’s cleaned up from the database?

I suspect I could answer most of these if I could figure out where in the database these are stored and just run through the scenarios, but any help on this would be much appreciated.

cody_c · May 28, 2020, 6:27pm

I guess what I’m getting at, is for the most part our foreman DB is pretty ephemeral. After a puppet run and a few sync commands, we can recover any Foreman instance back to a known working state. This is because of the puppet run adding hosts back in. If the Internal DB for IPs doesn’t recover as easily, I need a strategy of backing that up and restoring it if/when the host that is running foreman dies so that we can prevent doubling up IP assignments on provision.

lzap · May 29, 2020, 9:34am

Hello, there is no IPAM table in fact. Foreman actually picks either next IP in sequence or random IP and ensures there is no IP consumed by a NIC associated with that subnet.

https://docs.theforeman.org/guides/build/doc-Provisioning_Guide/index-foreman.html#networking_resources

lzap · May 29, 2020, 9:36am

Yeah, this is a lame check.

There was a suggestion from a community some time ago - if we added a new check: a DNS check. If there is an existing name present for that IP (PTR) the IP would be considered as used. If you like this feel free to contribute this, should be pretty easy to implement for smart proxy.

cody_c · May 29, 2020, 4:34pm

Right, it’s this bit:

Foreman finds the next available IP address from the Subnet range by excluding all IP addresses from the Foreman database randomly. The primary source of data is the database, not DHCP reservations.

That I’m curious about. What part of the database is it looking at to exclude all IPs from? Is this a complicated query to look up all Nics in a particular subnet? I’m just looking for where in the database host x has ip y associated to it. (or where in a series of tables if that turns out to be the case)

lzap · June 1, 2020, 1:20pm

You are looking for:

github.com

theforeman/foreman/blob/develop/app/services/ipam/random_db.rb

module IPAM
  # Internal DB IPAM returning all IPs in random order to minimize race conditions
  class RandomDb < Base
    def generator
      @generator ||= Random.new(mac ? mac.delete(':').to_i(16) : Random.new_seed)
    end

    def random_ip
      IPAddr.new(generator.rand(subnet_range.first.to_i..subnet_range.last.to_i), subnet.family)
    end

    # Safety check not to spend much CPU time when there are no many free IPs left. This gives up
    # in about a second on Ryzen 1700 running with Ruby 2.4.
    MAX_ITERATIONS = 100_000
    def suggest_ip
      iterations = 0
      loop do
        # next random IP from the sequence generated by MAC seed
        candidate = random_ip
        iterations += 1

This file has been truncated. show original

Or sequential:

github.com

theforeman/foreman/blob/develop/app/services/ipam/db.rb

module IPAM
  # Internal DB IPAM returning all IPs in natural order
  class Db < Base
    def suggest_ip
      subnet_range.each do |address|
        ip = address.to_s
        if !excluded_ips.include?(ip) && !subnet.known_ips.include?(ip)
          logger.debug("Found #{ip}")
          return ip
        end
      end
      logger.debug("Not suggesting IP Address for #{subnet} as no free IP found in our DB")
      errors.add(:subnet, _('no free IP could be found in our DB'))
      nil
    end
  end
end