Secure live migration with QEMU-native TLS

Context

The encryption offered by nova’s libvirt.live_migration_tunnelled does not secure all the different migration streams of a nova instance, namely: guest RAM, device state, and disks (via NBD) when using non-shared storage. Further, the “tunnelling via libvirtd” has inherent limitations: (a) it cannot handle live migration of disks in a non-shared storage setup (a.k.a. “block migration”); and (b) has a huge performance overhead and latency, because it burns more CPU and memory bandwidth due to increased number of data copies on both source and destination hosts.

To solve this existing limitation, QEMU and libvirt have gained (refer below for version details) support for “native TLS”, i.e. TLS built into QEMU. This will secure all data transports, including disks that are not on shared storage, without incurring the limitations of the “tunnelled via libvirtd” transport.

To take advantage of the “native TLS” support in QEMU and libvirt, nova has introduced new configuration attribute libvirt.live_migration_with_native_tls.

Prerequisites

  1. Version requirement: This feature needs at least libvirt 4.4.0 and QEMU 2.11.

  2. A pre-configured TLS environment—i.e. CA, server, and client certificates, their file permissions, et al—must be “correctly” configured (typically by an installer tool) on all relevant compute nodes. To simplify your PKI (Public Key Infrastructure) setup, use deployment tools that take care of handling all the certificate lifecycle management. For example, refer to the “TLS everywhere” guide from the TripleO project.

  3. Password-less SSH setup for all relevant compute nodes.

  4. On all relevant compute nodes, ensure the TLS-related config attributes in /etc/libvirt/qemu.conf are in place:

    default_tls_x509_cert_dir = "/etc/pki/qemu"
    default_tls_x509_verify = 1
    

    If it is not already configured, modify /etc/sysconfig/libvirtd on both (ComputeNode1 & ComputeNode2) to listen for TCP/IP connections:

    LIBVIRTD_ARGS="--listen"
    

    Then, restart the libvirt daemon (also on both nodes):

    $ systemctl restart libvirtd
    

    Refer to the “Related information” section on a note about the other TLS-related configuration attributes in /etc/libvirt/qemu.conf.

Validating your TLS environment on compute nodes

Assuming you have two compute hosts (ComputeNode1, and ComputeNode2) run the virt-pki-validate tool (comes with the libvirt-client package on your Linux distribution) on both the nodes to ensure all the necessary PKI files are configured are configured:

[ComputeNode1]$ virt-pki-validate
Found /usr/bin/certtool
Found CA certificate /etc/pki/CA/cacert.pem for TLS Migration Test
Found client certificate /etc/pki/libvirt/clientcert.pem for ComputeNode1
Found client private key /etc/pki/libvirt/private/clientkey.pem
Found server certificate /etc/pki/libvirt/servercert.pem for ComputeNode1
Found server private key /etc/pki/libvirt/private/serverkey.pem
Make sure /etc/sysconfig/libvirtd is setup to listen to
TCP/IP connections and restart the libvirtd service

[ComputeNode2]$ virt-pki-validate
Found /usr/bin/certtool
Found CA certificate /etc/pki/CA/cacert.pem for TLS Migration Test
Found client certificate /etc/pki/libvirt/clientcert.pem for ComputeNode2
Found client private key /etc/pki/libvirt/private/clientkey.pem
Found server certificate /etc/pki/libvirt/servercert.pem for ComputeNode2
Found server private key /etc/pki/libvirt/private/serverkey.pem
Make sure /etc/sysconfig/libvirtd is setup to listen to
TCP/IP connections and restart the libvirtd service

Performing the migration

  1. On all relevant compute nodes, enable the libvirt.live_migration_with_native_tls configuration attribute:

    [libvirt]
    live_migration_with_native_tls = true
    

    Note

    Setting both libvirt.live_migration_with_native_tls and libvirt.live_migration_tunnelled at the same time is invalid (and disallowed).

    And restart the nova-compute service:

    $ systemctl restart openstack-nova-compute
    
  2. Now that all TLS-related configuration is in place, migrate guests (with or without shared storage) from ComputeNode1 to ComputeNode2. Refer to the Live-migrate instances document on details about live migration.