userdoc:tt_high_availability [AstLinux Documentation]

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====== High Availability (keepalived) ======

AstLinux now supports the [[http://www.keepalived.org/|keepalived]] package, High Availability (HA) is achieved via the VRRP protocol. VRRP is a fundamental brick for implementing router failover.

Most AstLinux users will not have an occasion to use ''keepalived'', this is more of an enterprise level feature, but basic usage can be useful for certain AstLinux installations.

!!Note: AstLinux 1.3.4 or later is required!!

===== Keepalived Configuration =====

In AstLinux, ''keepalived'' is enabled by creating the configuration file, ''/mnt/kd/keepalived/keepalived.conf''

!!Tip ->!! After ''keepalived'' is started, the configuration file will be symlinked via ''/etc/keepalived/keepalived.conf''

The next section "Example Basic Configuration" shows a very basic starting point to build upon.

For reference, an updated list of ''keepalived.conf'' options is maintained here: [[https://raw.githubusercontent.com/acassen/keepalived/master/doc/keepalived.conf.SYNOPSIS|keepalived.conf Reference]]

After the ''/mnt/kd/keepalived/keepalived.conf'' is created, start the ''keepalived'' service via the CLI with:

  service keepalived init

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===== Example Basic Configuration =====

As a very basic example, we are creating a hot standby (backup) to a master AstLinux box.

!!Note ->!! For a production solution it is assumed that all the important file storage bits of the master are kept in sync with the backup AstLinux box.  Ignored for this example.

Both boxes share the same ''10.10.50.0/24'' network off the external interface ''eth0''.

The master box has a primary IPv4 of ''10.10.50.62''

The backup box has a primary IPv4 of ''10.10.50.65''

The virtual IPv4 address ''10.10.50.244'' labeled ''eth0:10'' will float between "master" and "backup", preferring "master" as long as it is available.

Master, primary IPv4: ''10.10.50.62''\\
Configuration: ''/mnt/kd/keepalived/keepalived.conf''

  ! Configuration File for keepalived
  
  global_defs {
    router_id ASTLINUX
    enable_script_security
    script_user root root
    vrrp_check_unicast_src
  }
  
  vrrp_instance VI_1 {
    state MASTER
    interface eth0
    virtual_router_id 50
    # How often to send out VRRP advertisements
    advert_int 1
    # The priority to assign to this device. This controls
    # who will become the MASTER and BACKUP for a given
    # VRRP instance (a lower number get's less priority)
    priority 100
  
    # Use unicast, multicast disabled
    unicast_src_ip 10.10.50.62
    unicast_peer {
      10.10.50.65
    }
  
    virtual_ipaddress {
      10.10.50.244 dev eth0 label eth0:10
    }
  }

Backup, primary IPv4: ''10.10.50.65''\\
Configuration: ''/mnt/kd/keepalived/keepalived.conf''

  ! Configuration File for keepalived
  
  global_defs {
    router_id ASTLINUX
    enable_script_security
    script_user root root
    vrrp_check_unicast_src
  }
  
  vrrp_instance VI_1 {
    state BACKUP
    interface eth0
    virtual_router_id 50
    # How often to send out VRRP advertisements
    advert_int 1
    # The priority to assign to this device. This controls
    # who will become the MASTER and BACKUP for a given
    # VRRP instance (a lower number get's less priority)
    priority 99
  
    # Use unicast, multicast disabled
    unicast_src_ip 10.10.50.65
    unicast_peer {
      10.10.50.62
    }
  
    virtual_ipaddress {
      10.10.50.244 dev eth0 label eth0:10
    }
  }

After the ''/mnt/kd/keepalived/keepalived.conf'' files are created, start the ''keepalived'' service on each box via the CLI with:

  service keepalived init

!!Tip ->!! Watch the VRRP packets with: ''tcpdump -i eth0 -vvn vrrp''

At this point on the master ''ip addr show dev eth0'' should display a line containing ''10.10.50.244''

  inet 10.10.50.244/32 scope global eth0:10

and the backup box should not display ''10.10.50.244'' .  Note that if something blocked VRRP packets between the boxes then both boxes would think they are the master and both would have ''10.10.50.244'' assigned, which is not good.  Only one occurrence of ''10.10.50.244'' should exist at a time.

Now test, disconnect the ''eth0'' cable from the master box ... watch the backup box acquire the ''10.10.50.244'' address, then reattach the network cable and watch ''10.10.50.244'' move back to the master.  For added fun, perform a ''ping 10.10.50.244'' from a local device and watch it (almost) not miss a beat during this test.

More testing, edit the ''/mnt/kd/keepalived/keepalived.conf'' file on the backup and change ''priority 99'' to ''priority 101'', restart ''keepalived'' by:

  service keepalived restart

now the backup box should be the master since it has a higher priority.  Undo the priority change and watch it return to normal.

Now you get the idea, to make this a production solution a few more details will need to be addressed, research the topic and build upon this basic example.

\\
===== Keepalived Scripts =====

More feature-rich ''keepalived.conf'' configurations will make use of external shell scripts, organize them in the ''/mnt/kd/keepalived/'' directory.  You may also refer to that directory as ''/etc/keepalived/'' in your ''keepalived.conf'' configuration.

If your scripts need a runtime, non-persistent state file, the ''/var/state/keepalived/'' directory is provided for such files.

\\

===== Firewall Configuration =====

For unicast ''keepalived'' configurations, it is not necessary to add firewall rules since the standard stateful connection tracking rules will allow inbound return packets from VRRP unicast peers you associate with.

If for some reason you prefer to use multicast instead of unicast packets, then you will need to configure the firewall to allow VRRP Multicasts.

Edit your ''/mnt/kd/arno-iptables-firewall/custom-rules'' file, and add this snippet.

  allow_ext_vrrp_mcast()
  {
    local src_list="$1" IFS
  
    echo "[CUSTOM RULE] Allowing external(INET) VRRP Multicasts from: $src_list"
    IFS=' ,'
    for src in $src_list; do
      iptables -A EXT_INPUT_CHAIN -p 112 -s $src -d 224.0.0.18 -j ACCEPT
    done
  }
  allow_ext_vrrp_mcast "10.10.50.0/24"

The ''allow_ext_vrrp_mcast'' argument can be a list of source IP's, network(s) or ''0/0'' to allow any source.