This is the first in a series of posts about my experience working with OpenShift and CNV (“Container Native Virtualization”, a technology that allows you to use OpenShift to manage virtualized workloads in addition to the containerized workloads for which OpenShift is known). In this post, I’ll be taking a look at the installation experience, and in particular at how restrictions in our local environment interacted with the network requirements of the installer.
We’re installing OpenShift on baremetal hosts using the IPI installer. “IPI” stands for “Installer Provisioned Infrastructure”, which means that the OpenShift installer is responsible for provisioning an operating system onto your hardware and managing the system configuration. This is in contrast to UPI (“User Provisioned Infrastructure”), in which you pre-provision the hosts using whatever tools you’re comfortable with and then point the installer and the hardware once things are up and running.
In the environment I’m working with, we had a few restrictions that I suspect are relatively common:
The network we were using as our “baremetal” network (for the purposes of this article you can read that as “public” network) does not have a dynamic pool of leases. There is DHCP, but all addresses are statically assigned.
Access to the IPMI network also requires a firewall exception for the host IP address.
When you’re reading through the installer documentation, the above requirements don’t seem problematic at first. Looking at the network requirements, you’ll see that the install calls for static addressing of all the hardware involved in the install:
Reserving IP Addresses for Nodes with the DHCP Server
For the baremetal network, a network administrator must reserve a number of IP addresses, including:
Three virtual IP addresses.
1 IP address for the API endpoint
1 IP address for the wildcard ingress endpoint
1 IP address for the name server
One IP Address for the Provisioning node.
One IP address for each Control Plane (Master) node.
One IP address for each worker node.
The “provisioning node” is the host on which you run the OpenShift installer. What the documentation fails to mention is that the services that manage the install don’t actually run on the provisioning node itself: instead, the installer starts up a “bootstrap virtual machine” on the provisioning node, and manages the install from there.
The bootstrap vm is directly attached to both the baremetal and the provisioning networks. It is created with a random MAC address, and relies on DHCP for configuring the baremetal interface. This means that:
It’s not possible to create a static DHCP lease for it, since you don’t know the MAC address ahead of time.
Since you can’t create a static DHCP lease, you can’t give it a static IP address.
Since you can’t give it a static IP address, you can’t create a firewall exception for access to the IPMI network.
And lastly, since you can’t create a static DHCP lease, you can’t conveniently use DHCP to assign the static route to the IPMI network.
This design decision – the use of a bootstrap vm with a random MAC address and no facility for assigning a static ip address – is what complicated our lives when we first set out to install OpenShift.
I’d like to emphasize that other than the issues discussed in the remainder of this article, the install process has been relatively smooth. We’re able to go from zero to a completely installed OpenShift cluster in just a few hours. There were some documentation issues early on, but I think most of those have already been resolved.
Attempted solution #1
OpenShift uses Ignition for performing host configuration tasks.
If you’re familiar with cloud-init, Ignition is doing something
very similar. One of the first things we tried was passing in a static
network configuration using Ignition. By running
openshift-baremetal-install create ignition-configs, it’s possible
to modify the ignition configuration passed into the bootstrap vm.
Unfortunately, it turns out that prior to loading the ignition
configuration, the bootstrap vm image will attempt to configure all
system interfaces using DHCP…and if it fails to acquire any
addresses, it just gives up.
In that case, it never gets as far as attempting to apply the ignition configuration, so this option didn’t work out.
Attempted solution #2
It is possible to pass a static ip configuration into the bootstrap vm by modifying the kernel command line parameters. There are several steps involved in creating a custom image:
- Parse through a JSON file to get URLs for the relevant images
- Download the images
- Uncompress the bootstrap image
virt-editto modify the grub configuration
- Calculate the uncompressed image checksum
- Re-compress the image
This also requires configuring your
install-config.yaml to use the
new image, and finding an appropriate place to host it.
This mechanism does work, but there are a lot of moving parts and in particular it seems like modifying the grub configuration could be a little tricky if the command line in the original image were to change in unexpected ways.
How we actually solved the problem
We ended up taking advantage of the fact that while we didn’t know the MAC address ahead of time, we did know the MAC address prefix ahead of time, so we created a small dynamic range (6 addresses) limited to that MAC prefix (which would match pretty much anything started by libvirt, but the only libvirt managed virtual machines attached to this network were OpenShift bootstrap vms). We were able to (a) attach the static route declaration to this small dynamic range, and (b) grant firewall exceptions for these specific addresses. The relevant lines in our dnsmasq configuration look something like:
dhcp-host=52:54:00:*:*:*,set:libvirt,set:ocp dhcp-range=tag:libvirt,10.1.2.130,10.1.2.135,255.255.255.0 dhcp-option=tag:ocp,option:classless-static-route,10.0.0.0/19,10.1.2.101
It’s not perfect, but it’s working fine.
What I would like to see
The baremetal installer should allow the deployer to pass in a
static address configuration for the bootstrap vm using the
install-config.yaml file. The bootstrap vm should continue to boot
even if it can’t initially configure an interface using DHCP (one
should be able to disable that initial DHCP attempt).