Virtualizzazione con Libvirt

la soluzione piu' comoda e open per Linux

Matteo Bernardini (matteo.bernardini _at_ gmail.com)
(nome di battaglia: ponce)

 

  • usa Linux da piu' di quattro lustri
  • esperienza lavorativa in diverse ditte ed enti pubblici italiani
  • dal 2008 molto attivo su Slackware (virtualizzazione, ambienti grafici leggeri, desktop remoti)
  • dal 2012 parte del gruppo di amministratori di SlackBuilds.org
  • gestisce personalmente un fork di questo repository con script di terze parti per la versione di sviluppo di Slackware

Un breve riepilogo della virtualizzazione in ambiente x86

 

1999 - VMware Workstation (ESX Server solo dal 2001)

1999 - User Mode Linux

2000 - FreeBSD supporta le jail

2001 - Linux VServer

2003 - qemu

2003 - Xen

2004 - Solaris Containers

2004 - Linux cpusets

2004 - Innotek Virtualbox

2005 - OpenVZ (Open Virtuozzo)

2005 - libvirt

2006 - Linux cgroups

2006 - qemu-kvm

2008 - Proxmox

2008 - Linux user namespaces

2008 - LXC

2013 - docker

2013 - lmctfy (-> libcontainer -> runc)

2014 - rkt

Virtualizzazione

con Hypervisor

I container condividono il kernel dell'host  e quindi sono molto meno pesanti della virtualizzazione dell'hardware. Volendo possono usare anche le librerie e i binari del  sistema operativo ospitante per far girare applicazioni (ad esempio tramite bind mount).

VANTAGGI DEGLI HYPERVISOR

 

  • si possono emulare sistemi operativi diversi da quello che gira sull'host virtualizzatore (Windows, i BSD, ecc.)
  • in generale sono considerati più sicuri, essendo più diffusi e piu' "anziani" (anche se ogni tanto esce qualche grossa vulnerabilita')

 

VANTAGGI DEI CONTAINER

 

  • le risorse occupate sono sensibilmente minori
  • se ne possono installare molti di più su un determinato hardware
  • sono molto più maneggevoli (tempi di avvio e spegnimento veloci, provisioning piu' semplice)

Cos'e' Libvirt?

 

E' una libreria scritta in C per gestire macchine virtuali

 

 

 

 

Gli hypervisor esistenti sono dinamici e spesso le interfacce da linea di comando cambiano o si evolvono: il vantaggio di libvirt e' che si puo' collegare a quasi tutti gli hypervisor esistenti offrendo un'interfaccia, una API e dei file di configurazione consistenti.

I file di configurazione sono scritti in xml.

 

A seconda dell'hypervisor sottostante non sono supportate tutte le funzionalita' ( tabella riassuntiva del supporto ).

demoni

 

libvirtd

fa tutto il lavoro

 

virtlogd

gestisce i log dei domini tramite socket dedicato: anche se e' accessibile solo tramite il demone principale e' stato deciso di usare un demone separato per evitare problemi derivanti dall'indisponibilita' dello stesso (riavvio, ecc.)

 

virtlockd

gestisce i lock sulle risorse assegnate ai domini tramite socket dedicato: anche se e' accessibile solo tramite il demone principale e' stato deciso di usare un demone separato per evitare problematiche analoghe a quelle di virtlogd.

Come funziona libvirt?

RETI VIRTUALI

 

 

 

 

 

Libvirt per default configura un network che usa NAT e le macchine virtuali sono in una rete privata 192.168.122.0/24.

 

In genere torna utile configurare le interfacce fisiche della macchina come bridge e far usare quelle alle macchine virtuali, che in questo modo possono utilizzare i network a cui sono collegate le interfacce (privato e pubblico, ad esempio).

 

Ovviamente con iptables (tramite gli nwfilters) si puo' implementare tutto quello che si vuole.

 

(per chi vuole approfondire e' disponibile il libvirt Networking Handbook)

Gestione da linea di comando: virsh

(nel gergo di libvirt l'host su cui gira e' indicato come "nodo"

e la macchina virtuale e' indicata come "dominio")

 

attivita' dei domini

start, shutdown, reboot, destroy, dumpxml

save, restore, suspend, resume, migrate

attach-device, attach-disk, attach-interface (e detach-*)

 

gestione dei dischi

(pool-*) list, info, dumpxml, define, edit, start, destroy,refresh

(vol-*) list, info, clone, create, delete, resize

 

gestione delle reti virtuali (net-*)

list, info, dumpxml, define, edit, start, destroy

monitoraggio dei domini (dom*)

 

informazioni sul nodo e l'hypervisor

 

interfacce di rete sull'host (iface-*)

 

filtri di rete (nwfilter-*)

 

periferiche dei nodi (nodedev-*)

 

gestione dei secret (secret-*)

 

snapshot (snapshot-*)

# virsh --help

virsh [options]... [<command_string>]
virsh [options]... <command> [args...]

  options:
    -c | --connect=URI      hypervisor connection URI
    -d | --debug=NUM        debug level [0-4]
    -e | --escape <char>    set escape sequence for console
    -h | --help             this help
    -k | --keepalive-interval=NUM
                            keepalive interval in seconds, 0 for disable
    -K | --keepalive-count=NUM
                            number of possible missed keepalive messages
    -l | --log=FILE         output logging to file
    -q | --quiet            quiet mode
    -r | --readonly         connect readonly
    -t | --timing           print timing information
    -v                      short version
    -V                      long version
         --version[=TYPE]   version, TYPE is short or long (default short)
  commands (non interactive mode):

 Domain Management (help keyword 'domain')
    attach-device                  attach device from an XML file
    attach-disk                    attach disk device
    attach-interface               attach network interface
    autostart                      autostart a domain
    blkdeviotune                   Set or query a block device I/O tuning parameters.
    blkiotune                      Get or set blkio parameters
    blockcommit                    Start a block commit operation.
    blockcopy                      Start a block copy operation.
    blockjob                       Manage active block operations
    blockpull                      Populate a disk from its backing image.
    blockresize                    Resize block device of domain.
    change-media                   Change media of CD or floppy drive
    console                        connect to the guest console
    cpu-stats                      show domain cpu statistics
    create                         create a domain from an XML file
    define                         define (but don't start) a domain from an XML file
    desc                           show or set domain's description or title
    destroy                        destroy (stop) a domain
    detach-device                  detach device from an XML file
    detach-device-alias            detach device from an alias
    detach-disk                    detach disk device
    detach-interface               detach network interface
    domdisplay                     domain display connection URI
    domfsfreeze                    Freeze domain's mounted filesystems.
    domfsthaw                      Thaw domain's mounted filesystems.
    domfsinfo                      Get information of domain's mounted filesystems.
    domfstrim                      Invoke fstrim on domain's mounted filesystems.
    domhostname                    print the domain's hostname
    domid                          convert a domain name or UUID to domain id
    domif-setlink                  set link state of a virtual interface
    domiftune                      get/set parameters of a virtual interface
    domjobabort                    abort active domain job
    domjobinfo                     domain job information
    domname                        convert a domain id or UUID to domain name
    domrename                      rename a domain
    dompmsuspend                   suspend a domain gracefully using power management functions
    dompmwakeup                    wakeup a domain from pmsuspended state
    domuuid                        convert a domain name or id to domain UUID
    domxml-from-native             Convert native config to domain XML
    domxml-to-native               Convert domain XML to native config
    dump                           dump the core of a domain to a file for analysis
    dumpxml                        domain information in XML
    edit                           edit XML configuration for a domain
    event                          Domain Events
    inject-nmi                     Inject NMI to the guest
    iothreadinfo                   view domain IOThreads
    iothreadpin                    control domain IOThread affinity
    iothreadadd                    add an IOThread to the guest domain
    iothreadset                    modifies an existing IOThread of the guest domain
    iothreaddel                    delete an IOThread from the guest domain
    send-key                       Send keycodes to the guest
    send-process-signal            Send signals to processes
    lxc-enter-namespace            LXC Guest Enter Namespace
    managedsave                    managed save of a domain state
    managedsave-remove             Remove managed save of a domain
    managedsave-edit               edit XML for a domain's managed save state file
    managedsave-dumpxml            Domain information of managed save state file in XML
    managedsave-define             redefine the XML for a domain's managed save state file
    memtune                        Get or set memory parameters
    perf                           Get or set perf event
    metadata                       show or set domain's custom XML metadata
    migrate                        migrate domain to another host
    migrate-setmaxdowntime         set maximum tolerable downtime
    migrate-getmaxdowntime         get maximum tolerable downtime
    migrate-compcache              get/set compression cache size
    migrate-setspeed               Set the maximum migration bandwidth
    migrate-getspeed               Get the maximum migration bandwidth
    migrate-postcopy               Switch running migration from pre-copy to post-copy
    numatune                       Get or set numa parameters
    qemu-attach                    QEMU Attach
    qemu-monitor-command           QEMU Monitor Command
    qemu-monitor-event             QEMU Monitor Events
    qemu-agent-command             QEMU Guest Agent Command
    reboot                         reboot a domain
    reset                          reset a domain
    restore                        restore a domain from a saved state in a file
    resume                         resume a domain
    save                           save a domain state to a file
    save-image-define              redefine the XML for a domain's saved state file
    save-image-dumpxml             saved state domain information in XML
    save-image-edit                edit XML for a domain's saved state file
    schedinfo                      show/set scheduler parameters
    screenshot                     take a screenshot of a current domain console and store it into a file
    set-lifecycle-action           change lifecycle actions
    set-user-password              set the user password inside the domain
    setmaxmem                      change maximum memory limit
    setmem                         change memory allocation
    setvcpus                       change number of virtual CPUs
    shutdown                       gracefully shutdown a domain
    start                          start a (previously defined) inactive domain
    suspend                        suspend a domain
    ttyconsole                     tty console
    undefine                       undefine a domain
    update-device                  update device from an XML file
    vcpucount                      domain vcpu counts
    vcpuinfo                       detailed domain vcpu information
    vcpupin                        control or query domain vcpu affinity
    emulatorpin                    control or query domain emulator affinity
    vncdisplay                     vnc display
    guestvcpus                     query or modify state of vcpu in the guest (via agent)
    setvcpu                        attach/detach vcpu or groups of threads
    domblkthreshold                set the threshold for block-threshold event for a given block device or it's backing chain element
    guestinfo                      query information about the guest (via agent)

 Domain Monitoring (help keyword 'monitor')
    domblkerror                    Show errors on block devices
    domblkinfo                     domain block device size information
    domblklist                     list all domain blocks
    domblkstat                     get device block stats for a domain
    domcontrol                     domain control interface state
    domif-getlink                  get link state of a virtual interface
    domifaddr                      Get network interfaces' addresses for a running domain
    domiflist                      list all domain virtual interfaces
    domifstat                      get network interface stats for a domain
    dominfo                        domain information
    dommemstat                     get memory statistics for a domain
    domstate                       domain state
    domstats                       get statistics about one or multiple domains
    domtime                        domain time
    list                           list domains
 Host and Hypervisor (help keyword 'host')
    allocpages                     Manipulate pages pool size
    capabilities                   capabilities
    cpu-baseline                   compute baseline CPU
    cpu-compare                    compare host CPU with a CPU described by an XML file
    cpu-models                     CPU models
    domcapabilities                domain capabilities
    freecell                       NUMA free memory
    freepages                      NUMA free pages
    hostname                       print the hypervisor hostname
    hypervisor-cpu-baseline        compute baseline CPU usable by a specific hypervisor
    hypervisor-cpu-compare         compare a CPU with the CPU created by a hypervisor on the host
    maxvcpus                       connection vcpu maximum
    node-memory-tune               Get or set node memory parameters
    nodecpumap                     node cpu map
    nodecpustats                   Prints cpu stats of the node.
    nodeinfo                       node information
    nodememstats                   Prints memory stats of the node.
    nodesuspend                    suspend the host node for a given time duration
    sysinfo                        print the hypervisor sysinfo
    uri                            print the hypervisor canonical URI
    version                        show version

 Checkpoint (help keyword 'checkpoint')
    checkpoint-create              Create a checkpoint from XML
    checkpoint-create-as           Create a checkpoint from a set of args
    checkpoint-delete              Delete a domain checkpoint
    checkpoint-dumpxml             Dump XML for a domain checkpoint
    checkpoint-edit                edit XML for a checkpoint
    checkpoint-info                checkpoint information
    checkpoint-list                List checkpoints for a domain
    checkpoint-parent              Get the name of the parent of a checkpoint

 Interface (help keyword 'interface')
    iface-begin                    create a snapshot of current interfaces settings, which can be later committed (iface-commit) or restored (iface-rollback)
    iface-bridge                   create a bridge device and attach an existing network device to it
    iface-commit                   commit changes made since iface-begin and free restore point
    iface-define                   define an inactive persistent physical host interface or modify an existing persistent one from an XML file
    iface-destroy                  destroy a physical host interface (disable it / "if-down")
    iface-dumpxml                  interface information in XML
    iface-edit                     edit XML configuration for a physical host interface
    iface-list                     list physical host interfaces
    iface-mac                      convert an interface name to interface MAC address
    iface-name                     convert an interface MAC address to interface name
    iface-rollback                 rollback to previous saved configuration created via iface-begin
    iface-start                    start a physical host interface (enable it / "if-up")
    iface-unbridge                 undefine a bridge device after detaching its slave device
    iface-undefine                 undefine a physical host interface (remove it from configuration)

 Network Filter (help keyword 'filter')
    nwfilter-define                define or update a network filter from an XML file
    nwfilter-dumpxml               network filter information in XML
    nwfilter-edit                  edit XML configuration for a network filter
    nwfilter-list                  list network filters
    nwfilter-undefine              undefine a network filter
    nwfilter-binding-create        create a network filter binding from an XML file
    nwfilter-binding-delete        delete a network filter binding
    nwfilter-binding-dumpxml       network filter information in XML
    nwfilter-binding-list          list network filter bindings

 Networking (help keyword 'network')
    net-autostart                  autostart a network
    net-create                     create a network from an XML file
    net-define                     define an inactive persistent virtual network or modify an existing persistent one from an XML file
    net-destroy                    destroy (stop) a network
    net-dhcp-leases                print lease info for a given network
    net-dumpxml                    network information in XML
    net-edit                       edit XML configuration for a network
    net-event                      Network Events
    net-info                       network information
    net-name                       convert a network UUID to network name
    net-start                      start a (previously defined) inactive network
    net-undefine                   undefine a persistent network
    net-update                     update parts of an existing network's configuration
    net-uuid                       convert a network name to network UUID
    net-port-list                  list network ports
    net-port-create                create a network port from an XML file
    net-port-dumpxml               network port information in XML
    net-port-delete                delete the specified network port

 Node Device (help keyword 'nodedev')
    nodedev-create                 create a device defined by an XML file on the node
    nodedev-destroy                destroy (stop) a device on the node
    nodedev-detach                 detach node device from its device driver
    nodedev-dumpxml                node device details in XML
    nodedev-list                   enumerate devices on this host
    nodedev-reattach               reattach node device to its device driver
    nodedev-reset                  reset node device
    nodedev-event                  Node Device Events

 Secret (help keyword 'secret')
    secret-define                  define or modify a secret from an XML file
    secret-dumpxml                 secret attributes in XML
    secret-event                   Secret Events
    secret-get-value               Output a secret value
    secret-list                    list secrets
    secret-set-value               set a secret value
    secret-undefine                undefine a secret

 Snapshot (help keyword 'snapshot')
    snapshot-create                Create a snapshot from XML
    snapshot-create-as             Create a snapshot from a set of args
    snapshot-current               Get or set the current snapshot
    snapshot-delete                Delete a domain snapshot
    snapshot-dumpxml               Dump XML for a domain snapshot
    snapshot-edit                  edit XML for a snapshot
    snapshot-info                  snapshot information
    snapshot-list                  List snapshots for a domain
    snapshot-parent                Get the name of the parent of a snapshot
    snapshot-revert                Revert a domain to a snapshot

 Storage Pool (help keyword 'pool')
    find-storage-pool-sources-as   find potential storage pool sources
    find-storage-pool-sources      discover potential storage pool sources
    pool-autostart                 autostart a pool
    pool-build                     build a pool
    pool-create-as                 create a pool from a set of args
    pool-create                    create a pool from an XML file
    pool-define-as                 define a pool from a set of args
    pool-define                    define an inactive persistent storage pool or modify an existing persistent one from an XML file
    pool-delete                    delete a pool
    pool-destroy                   destroy (stop) a pool
    pool-dumpxml                   pool information in XML
    pool-edit                      edit XML configuration for a storage pool
    pool-info                      storage pool information
    pool-list                      list pools
    pool-name                      convert a pool UUID to pool name
    pool-refresh                   refresh a pool
    pool-start                     start a (previously defined) inactive pool
    pool-undefine                  undefine an inactive pool
    pool-uuid                      convert a pool name to pool UUID
    pool-event                     Storage Pool Events
    pool-capabilities              storage pool capabilities

 Storage Volume (help keyword 'volume')
    vol-clone                      clone a volume.
    vol-create-as                  create a volume from a set of args
    vol-create                     create a vol from an XML file
    vol-create-from                create a vol, using another volume as input
    vol-delete                     delete a vol
    vol-download                   download volume contents to a file
    vol-dumpxml                    vol information in XML
    vol-info                       storage vol information
    vol-key                        returns the volume key for a given volume name or path
    vol-list                       list vols
    vol-name                       returns the volume name for a given volume key or path
    vol-path                       returns the volume path for a given volume name or key
    vol-pool                       returns the storage pool for a given volume key or path
    vol-resize                     resize a vol
    vol-upload                     upload file contents to a volume
    vol-wipe                       wipe a vol

 Virsh itself (help keyword 'virsh')
    cd                             change the current directory
    echo                           echo arguments
    exit                           quit this interactive terminal
    help                           print help
    pwd                            print the current directory
    quit                           quit this interactive terminal
    connect                        (re)connect to hypervisor


  (specify help <group> for details about the commands in the group)

  (specify help <command> for details about the command)

Di default l'interfaccia a linea di comando si collega a

 

qemu

 

software che implementa un particolare sistema di emulazione che permette di ottenere un'architettura informatica nuova e disgiunta in un'altra che si occuperà di ospitarla.

 

E' stato scritto da Fabrice Bellard, creatore, tra le altre mille cose, anche di ffmpeg.

 

Dalla sua integrazione col progetto KVM puo' anche operare in modo da utilizzare le estensioni della CPU, se disponibili, attraverso un modulo del kernel al posto dell'emulazione: in questo modo le macchine virtuali sono parecchio piu' reattive ed efficienti.

virsh opera collegato agli hypervisor e vi si connette tramite il suo URI (conformi alle specifiche dell'RFC 2396)

 

qemu:///system

lxc:///system

xen:///system

vbox:///session

vmware://{vpx,esx,gsx}

hyperv://

 

si possono definire degli alias nei file di configurazione

uri_aliases = [
  "hail=qemu+ssh://root@hail.cloud.example.com/system",
  "sleet=qemu+ssh://root@sleet.cloud.example.com/system",
]

ci si puo' collegare a libvirtd tramite socket locale accessibile al gruppo con cui abbiamo deciso di far girare il demone (/var/run/libvirt/libvirt-sock e /var/run/libvirt/libvirt-sock), ma si puo', in alternativa usare anche un'autentica tramite SASL (utente/password o kerberos).

 

il vettore di collegamento remoto e' principalmente ssh, ma si puo' usare anche tls o varianti implementative di ssh, come libssh/libssh2, o un collegamento tcp in chiaro (ovviamente sconsigliato se non su reti dedicate).

 

tramite policykit si puo' restringere l'accesso in modo granulare usando access list

 

https://libvirt.org/remote.html

Offre un'interfaccia di programmazione per molti linguaggi:

 

C

Python

Go

Perl

Objective Caml

Ruby

Java

Php

C#

Dbus

ecc.

CONVERTIRE / MANIPOLARE IMMAGINI DISCO

 

libguestfs

 

libreria per accedere e interagire con immagini disco: supporta moltissimi formati.

puo' agire tramite una shell scriptabile, guestfish o una rescue shell interattiva, virt-rescue.

per avere un'idea di quello che puo' fare date un'occhiata alle ricette.

 

qemu-img convert

 

supporta diversi formati:

QCOW2 (KVM, Xen), raw, VDI (VirtualBox), VHD (Hyper-V), VMDK (VMware)

 

qemu-img convert -f raw -O qcow2 image.img image.qcow2

VIRT-MANAGER

 

GUI principale per l'amministrazione da remoto.

 

E' pensata principalmente per macchine virtuali che utilizzano KVM, ma funziona anche con container LXC e domini Xen.

Mostra una visione d'insieme dei domini in esecuzione, delle loro prestazioni in tempo reale e delle statistiche sull'utilizzo delle risorse.

Offre procedure guidate per la creazione dei domini e per l'allocazione a quest'ultimi di risorse e di hardware virtuale.

Sono disponibili dei visualizzatori delle console grafiche remote delle macchine virtuali sia tramite il protocollo VNC che quello SPICE.

 

-  SESSIONE PRATICA -

 

DOMANDE?

Virtualizzazione con Libvirt

By Matteo Bernardini

Virtualizzazione con Libvirt

  • 169
Loading comments...

More from Matteo Bernardini