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diff --git a/docs/configuration/highavailability/index.rst b/docs/configuration/highavailability/index.rst new file mode 100644 index 00000000..a223c283 --- /dev/null +++ b/docs/configuration/highavailability/index.rst @@ -0,0 +1,191 @@ +.. _high-availability: + +High availability +================= + +VRRP (Virtual Router Redundancy Protocol) provides active/backup redundancy for +routers. Every VRRP router has a physical IP/IPv6 address, and a virtual +address. On startup, routers elect the master, and the router with the highest +priority becomes the master and assigns the virtual address to its interface. +All routers with lower priorities become backup routers. The master then starts +sending keepalive packets to notify other routers that it's available. If the +master fails and stops sending keepalive packets, the router with the next +highest priority becomes the new master and takes over the virtual address. + +VRRP keepalive packets use multicast, and VRRP setups are limited to a single +datalink layer segment. You can setup multiple VRRP groups +(also called virtual routers). Virtual routers are identified by a +VRID (Virtual Router IDentifier). If you setup multiple groups on the same +interface, their VRIDs must be unique, but it's possible (even if not +recommended for readability reasons) to use duplicate VRIDs on different +interfaces. + +Basic setup +----------- + +VRRP groups are created with the +``set high-availability vrrp group $GROUP_NAME`` commands. The required +parameters are interface, vrid, and virtual-address. + +minimal config + +.. code-block:: none + + set high-availability vrrp group Foo vrid 10 + set high-availability vrrp group Foo interface eth0 + set high-availability vrrp group Foo virtual-address 192.0.2.1/24 + +You can verify your VRRP group status with the operational mode +``run show vrrp`` command: + +.. code-block:: none + + vyos@vyos# run show vrrp + Name Interface VRID State Last Transition + ---------- ----------- ------ ------- ----------------- + Foo eth1 10 MASTER 2s + +IPv6 support +------------ + +The ``virtual-address`` parameter can be either an IPv4 or IPv6 address, but you +cannot mix IPv4 and IPv6 in the same group, and will need to create groups with +different VRIDs specially for IPv4 and IPv6. + +Disabling a VRRP group +---------------------- + +You can disable a VRRP group with ``disable`` option: + +.. code-block:: none + + set high-availability vrrp group Foo disable + +A disabled group will be removed from the VRRP process and your router will not +participate in VRRP for that VRID. It will disappear from operational mode +commands output, rather than enter the backup state. + +Setting VRRP group priority +--------------------------- + +VRRP priority can be set with ``priority`` option: + +.. code-block:: none + + set high-availability vrrp group Foo priority 200 + +The priority must be an integer number from 1 to 255. Higher priority value +increases router's precedence in the master elections. + +Sync groups +----------- + +A sync group allows VRRP groups to transition together. + +.. code-block:: none + + edit high-availability vrrp + set sync-group MAIN member VLAN9 + set sync-group MAIN member VLAN20 + +In the following example, when VLAN9 transitions, VLAN20 will also transition: + +.. code-block:: none + + vrrp { + group VLAN9 { + interface eth0.9 + virtual-address 10.9.1.1/24 + priority 200 + vrid 9 + } + group VLAN20 { + interface eth0.20 + priority 200 + virtual-address 10.20.20.1/24 + vrid 20 + } + sync-group MAIN { + member VLAN20 + member VLAN9 + } + } + + +.. warning:: All items in a sync group should be similarly configured. + If one VRRP group is set to a different premption delay or priority, + it would result in an endless transition loop. + + +Preemption +---------- + +VRRP can use two modes: preemptive and non-preemptive. In the preemptive mode, +if a router with a higher priority fails and then comes back, routers with lower +priority will give up their master status. In non-preemptive mode, the newly +elected master will keep the master status and the virtual address indefinitely. + +By default VRRP uses preemption. You can disable it with the "no-preempt" +option: + +.. code-block:: none + + set high-availability vrrp group Foo no-preempt + +You can also configure the time interval for preemption with the "preempt-delay" +option. For example, to set the higher priority router to take over in 180 +seconds, use: + +.. code-block:: none + + set high-availability vrrp group Foo preempt-delay 180 + +Unicast VRRP +------------ + +By default VRRP uses multicast packets. If your network does not support +multicast for whatever reason, you can make VRRP use unicast communication +instead. + +.. code-block:: none + + set high-availability vrrp group Foo peer-address 192.0.2.10 + set high-availability vrrp group Foo hello-source-address 192.0.2.15 + +Scripting +--------- + +VRRP functionality can be extended with scripts. VyOS supports two kinds of +scripts: health check scripts and transition scripts. Health check scripts +execute custom checks in addition to the master router reachability. Transition +scripts are executed when VRRP state changes from master to backup or fault and +vice versa and can be used to enable or disable certain services, for example. + +Health check scripts +^^^^^^^^^^^^^^^^^^^^ + +This setup will make the VRRP process execute the +``/config/scripts/vrrp-check.sh script`` every 60 seconds, and transition the +group to the fault state if it fails (i.e. exits with non-zero status) three +times: + +.. code-block:: none + + set high-availability vrrp group Foo health-check script /config/scripts/vrrp-check.sh + set high-availability vrrp group Foo health-check interval 60 + set high-availability vrrp group Foo health-check failure-count 3 + +Transition scripts +^^^^^^^^^^^^^^^^^^ + +Transition scripts can help you implement various fixups, such as starting and +stopping services, or even modifying the VyOS config on VRRP transition. +This setup will make the VRRP process execute the +``/config/scripts/vrrp-fail.sh`` with argument ``Foo`` when VRRP fails, +and the ``/config/scripts/vrrp-master.sh`` when the router becomes the master: + +.. code-block:: none + + set high-availability vrrp group Foo transition-script backup "/config/scripts/vrrp-fail.sh Foo" + set high-availability vrrp group Foo transition-script fault "/config/scripts/vrrp-fail.sh Foo" + set high-availability vrrp group Foo transition-script master "/config/scripts/vrrp-master.sh Foo" |