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Libvirt HOWTO

Launching clusters via libvirt is especially useful for operator development.

NOTE: Some aspects of the installation can be customized through the install-config.yaml file. See how to create an install-config.yaml file and the libvirt platform customization documents.

One-time setup

It's expected that you will create and destroy clusters often in the course of development. These steps only need to be run once.

Before you begin, install the build dependencies.

Enable KVM

Make sure you have KVM enabled by checking for the device:

$ ls -l /dev/kvm
crw-rw-rw-+ 1 root kvm 10, 232 Oct 31 09:22 /dev/kvm

If it is missing, try some of the ideas here.

Install and Enable Libvirt

On CentOS 7, first enable the kvm-common repository to ensure you get a new enough version of qemu-kvm.

On Fedora, CentOS/RHEL:

sudo yum install libvirt-devel libvirt-daemon-kvm libvirt-client

Then start libvirtd:

sudo systemctl enable --now libvirtd

Pick names

In this example, we'll set the base domain to tt.testing and the cluster name to test1.

Clone the project

git clone https://github.com/openshift/installer.git
cd installer

Enable IP Forwarding

Libvirt creates a bridged connection to the host machine, but in order for the network bridge to work IP forwarding needs to be enabled. The following command will tell you if forwarding is enabled:

sysctl net.ipv4.ip_forward

If the command output is:

net.ipv4.ip_forward = 0

then forwarding is disabled and proceed with the rest of this section. If IP forwarding is enabled then skip the rest of this section.

To enable IP forwarding for the current boot:

sysctl net.ipv4.ip_forward=1

or to persist the setting across reboots (recommended):

echo "net.ipv4.ip_forward = 1" | sudo tee /etc/sysctl.d/99-ipforward.conf
sudo sysctl -p /etc/sysctl.d/99-ipforward.conf

Configure libvirt to accept TCP connections

The Kubernetes cluster-api components drive deployment of worker machines. The libvirt cluster-api provider will run inside the local cluster, and will need to connect back to the libvirt instance on the host machine to deploy workers.

In order for this to work, you'll need to enable unauthenticated TCP connections for libvirt.

NOTE: The following configuration disables all encryption and authentication options in libvirtd and causes it to listen on all network interfaces and IP addresses. A connection to this privileged libvirtd gives the client privileges equivalent to those of a root shell. This configuration has a security impact on a par with running a telnet server with no root password set. It is critical to follow the steps below to configure the firewall to prevent access to libvirt from other hosts on the LAN/WAN.

For systemd activated libvirt

This applies only if the libvirt daemon is configured to use socket activation. This is currently the case on Fedora 31 (and later) and Arch Linux.

First, you need to start the libvirtd TCP socket, which is managed by systemd:

sudo systemctl start libvirtd-tcp.socket

To make this change persistent across reboots you can optionally enable it:

sudo systemctl enable libvirtd-tcp.socket

Then to enable TCP access to libvirtd, modify /etc/libvirt/libvirtd.conf and set the following:

auth_tcp = "none"

Then restart libvirt:

sudo systemctl restart libvirtd

For permanently running libvirt daemon

This applies only if the libvirt daemon is started only through libvirtd.service and without making use of systemd socket activation (through libvirtd.socket and similar systemd units).

For RHEL/CentOS, make sure that the following is set in /etc/sysconfig/libvirtd:

LIBVIRTD_ARGS="--listen"

For Debian based distros, make sure that the following is set in /etc/default/libvirtd:

libvirtd_opts="--listen"

Then to enable TCP access to libvirtd, modify /etc/libvirt/libvirtd.conf and set the following:

listen_tls = 0
listen_tcp = 1
auth_tcp = "none"
tcp_port = "16509"

Then restart libvirt:

sudo systemctl restart libvirtd

Configure qemu.conf

On Debian/Ubuntu it might be needed to configure security driver for qemu. Installer uses terraform libvirt, and it has a known issue, that might cause unexpected Could not open '/var/lib/libvirt/images/<FILE_NAME>': Permission denied errors. Double check that security_driver = "none" line is present in /etc/libvirt/qemu.conf and not commented out.

Firewall

Finally, if you have a firewall, you may have to allow connections to the libvirt daemon from the IP range used by your cluster nodes.

The following examples use the default cluster IP range of 192.168.126.0/24 (which is currently not configurable) and a libvirt default subnet of 192.168.122.0/24, which might be different in your configuration. If you're uncertain about the libvirt default subnet you should be able to see its address using the command ip -4 a show dev virbr0 or by inspecting virsh --connect qemu:///system net-dumpxml default. Ensure the cluster IP range does not overlap your virbr0 IP address.

iptables

sudo iptables -I INPUT -p tcp -s 192.168.126.0/24 -d 192.168.122.1 --dport 16509 -j ACCEPT -m comment --comment "Allow insecure libvirt clients"

Firewalld

If using firewalld, the specifics will depend on how your distribution has set up the various zones. The following instructions should work as is for Fedora, CentOS, RHEL and Arch Linux.

First, as we don't want to expose the libvirt port externally, we will need to actively block it:

sudo firewall-cmd --add-rich-rule "rule service name="libvirt" reject"

For systems with libvirt version 5.1.0 and later, libvirt will set new bridged network interfaces in the libvirt zone. We thus need to allow libvirt traffic from the VMs to reach the host:

sudo firewall-cmd --zone=libvirt --add-service=libvirt

For system with an older libvirt, we will move the new bridge interface to a dedicated network zone and enable incoming libvirt, DNS & DHCP traffic:

sudo firewall-cmd --zone=dmz --change-interface=tt0
sudo firewall-cmd --zone=dmz --add-service=libvirt
sudo firewall-cmd --zone=dmz --add-service=dns
sudo firewall-cmd --zone=dmz --add-service=dhcp

NOTE: When the firewall rules are no longer needed, sudo firewall-cmd --reload will remove the changes made as they were not permanently added. For persistence, add --permanent to the firewall-cmd commands and run them a second time.

Set up DNS

This step allows installer and users to resolve cluster-internal hostnames from your host.

Using systemd-resolved

If your system is using systemd-resolved (the default since Fedora 33), then you can setup DNS without using dnsmasq.

Just point resolvectl to use 192.168.126.1 for your baseDomain. Replace baseDomain in the example accordingly.

sudo resolvectl dns tt0 192.168.126.1
sudo resolvectl domain tt0 ~<baseDomain>

Your cluster might run on a different network interface. To find which one it is, either check your install-config.yaml or run nmcli and find the interface that's running the 192.168.126.0/24 net.

Please note that this is not persistent across libvirt network creation/deletion of the tt0 interface. Once the tt0 interface is deleted and recreated, it will need to be updated again with the proper resolver.

Using NetworkManager DNS overlay

  1. Tell NetworkManager to use dnsmasq:

    echo -e "[main]\ndns=dnsmasq" | sudo tee /etc/NetworkManager/conf.d/openshift.conf

  2. Tell dnsmasq to use your cluster. The syntax is server=/<baseDomain>/<firstIP>.

    For this example:

    echo server=/tt.testing/192.168.126.1 | sudo tee /etc/NetworkManager/dnsmasq.d/openshift.conf

  3. Reload NetworkManager to pick up the dns configuration change: sudo systemctl reload NetworkManager

Build the installer

Set TAGS=libvirt to add support for libvirt; this is not enabled by default because libvirt is development only.

TAGS=libvirt hack/build.sh

Run the installer

With libvirt configured, you can proceed with the usual quick-start.

Cleanup

To remove resources associated with your cluster, run:

openshift-install destroy cluster

You can also use virsh-cleanup.sh, but note that it will currently destroy all libvirt resources.

Firewall

With the cluster removed, you no longer need to allow libvirt nodes to reach your libvirtd. Restart firewalld to remove your temporary changes as follows:

sudo firewall-cmd --reload

Exploring your cluster

Some things you can do:

SSH access

The bootstrap node, e.g. test1-bootstrap.tt.testing, runs the bootstrap process. You can watch it:

ssh "core@${CLUSTER_NAME}-bootstrap.${BASE_DOMAIN}"
sudo journalctl -f -u bootkube -u openshift

You'll have to wait for etcd to reach quorum before this makes any progress.

Using the domain names above will only work if you set up the DNS overlay or have otherwise configured your system to resolve cluster domain names. Alternatively, if you didn't set up DNS on the host, you can use:

virsh -c "${LIBVIRT_URI}" domifaddr "${CLUSTER_NAME}-master-0"  # to get the master IP
ssh core@$MASTER_IP

Here LIBVIRT_URI is the libvirt connection URI which you passed to the installer.

Inspect the cluster with kubectl

You'll need a kubectl binary on your path and the kubeconfig from your cluster call.

export KUBECONFIG="${DIR}/auth/kubeconfig"
kubectl get --all-namespaces pods

Alternatively, you can run kubectl from the bootstrap or master nodes. Use scp or similar to transfer your local ${DIR}/auth/kubeconfig, then SSH in and run:

export KUBECONFIG=/where/you/put/your/kubeconfig
kubectl get --all-namespaces pods

FAQ

Libvirt vs. AWS

  1. There isn't a load balancer on libvirt.

Troubleshooting

If following the above steps hasn't quite worked, please review this section for well known issues.

Console doesn't come up

In case of libvirt there is no wildcard DNS resolution and console depends on the route which is created by auth operator (Issue #1007). To make it work we need to first create the manifests and edit the domain for ingress config, before directly creating the cluster.

  • Add another domain entry in the openshift.conf which used by dnsmasq. Here tt.testing is the domain which I choose when running the installer. Here the IP in the address belong to one of the worker node.
$ cat /etc/NetworkManager/dnsmasq.d/openshift.conf
server=/tt.testing/192.168.126.1
address=/.apps.tt.testing/192.168.126.51
  • An alternate method to specify the dnsmasq option, if the system is using libvirt version 5.6.0+, is to specify the option in the install config under the platform's network section in the following way.
    platform:
      libvirt:
        network:
          dnsmasqOptions:
          - name: "address"
            value: "/.apps.tt.testing/192.168.126.51"
          if: tt0
  • Make sure you restart the NetworkManager after change in openshift.conf:
$ sudo systemctl restart NetworkManager
  • Create the manifests:
$ openshift-install --dir $INSTALL_DIR create manifests
  • Domain entry in cluster-ingress-02-config.yml file should not contain cluster name:
# Assuming `test1` as cluster name
$ sed -i 's/test1.//' $INSTALL_DIR/manifests/cluster-ingress-02-config.yml
  • Start the installer to create the cluster:
$ openshift-install --dir $INSTALL_DIR create cluster

Install throws an Unable to resolve address 'localhost' error

If you're seeing an error similar to

Error: Error refreshing state: 1 error(s) occurred:

* provider.libvirt: virError(Code=38, Domain=7, Message='Unable to resolve address 'localhost' service '-1': Servname not supported for ai_socktype')


FATA[0019] failed to run Terraform: exit status 1

it is likely that your install configuration contains three backslashes after the protocol (e.g. qemu+tcp:///...), when it should only be two.

Random domain creation errors due to libvirt race condition

Depending on your libvirt version you might encounter a race condition leading to an error similar to:

* libvirt_domain.master.0: Error creating libvirt domain: virError(Code=43, Domain=19, Message='Network not found: no network with matching name 'test1'')

This is also being tracked on the libvirt-terraform-provider but is likely not fixable on the client side, which is why you should upgrade libvirt to >=4.5 or a patched version, depending on your environment.

MacOS support currently broken

Error with firewall initialization on Arch Linux

If you're on Arch Linux and get an error similar to

libvirt: “Failed to initialize a valid firewall backend”

or

error: Failed to start network default
error: internal error: Failed to initialize a valid firewall backend

please check out this thread on superuser.

GitHub Issue Tracker

You might find other reports of your problem in the Issues tab for this repository where we ask you to provide any additional information. If your issue is not reported, please do.