Manual Chapter : Managing Failover

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BIG-IP LTM

  • 15.0.0
Manual Chapter

Managing Failover

Managing failover using HA groups

Sometimes a traffic group within a BIG-IP® Sync-Failover device group needs a certain number of resources to be up -- resources like pool members, trunk links, VIPRION ®cluster members, or some combination of these.
With
HA groups
, you can define the minimum number of resources that a traffic group needs for it to stay active on its current device. If resources fall below that number, the traffic group fails over to a device with more resources. An HA group:
  • Monitors resource availability on current and next-active devices for an active traffic group
  • Calculates an HA "resource" score on each device for choosing the next-active device
For an HA group to prevent a traffic group from failing over,
all
of the resource types that you specify in an HA group must meet the defined minimum thresholds for availability.

Creating an HA group

You use this task to create an HA group for a traffic group on a device in a BIG-IP device group. An HA group is most useful when you want an active traffic group on a device to fail over to another device based on trunk and pool availability, and on VIPRION systems, also cluster availability. You can create multiple HA groups on a single BIG-IP device, and you associate each HA group with the local instance of a traffic group.
Once you create an HA group on one device and associate the HA group with a traffic group, you must create an HA group on every other device in the device group and associate it with that same traffic group.
  1. Log in to a device in the device group (such as
    BIG-IP A
    ), using the device's management IP address.
    The login screen of the BIG-IP Configuration utility opens.
  2. On the Main tab, click
    System
    High Availability
    HA Groups
  3. Click
    Create
    .
  4. In the
    HA Group Name
    field, type a name such as
    ha_group_deviceA_tg1
    .
  5. In the
    Active Bonus
    field, keep the default value.
    The purpose of the active bonus is to boost the HA score to prevent failover when minor or frequent changes occur to the availability of a pool, trunk, or cluster.
  6. In the Pools area of the screen, click
    Add
    .
    If the
    Add
    button is grayed out, there are no pools on the BIG-IP system.
    The
    Add Pool to HA Group
    dialog box appears.
  7. From the
    Pool
    list, select a pool name.
  8. Using the drop-down list, select the minimum number of active pool members required for this device to process traffic.
    This value is the minimum number of pool members that you want to be up in order for the active instance of a specific traffic group to remain on its current device. You will assign this HA group to the traffic group later.
  9. In the weight field, retain the default value or type a value and for the number of active pool members that are sufficient to be up for calculating the weight, select a value.
    For example, if the total number of pool members is
    6
    , but the value of the
    Sufficient Threshold
    setting is
    4
    and there are only two pool members currently available, the BIG-IP system calculates the score by multiplying the weight you configured for the pool by the percentage of pool members available as compared to the
    sufficient value
    , not to the total number of pool members. If the weight we configure for the pool is
    50
    , and 50% of the pool members are up (2 of 4), then the HA score calculation for the pool is 50 x 50% = 25.
  10. Click
    Add
    .
    This displays the New HA Group screen and shows the pool member criteria that must be met to prevent the traffic group from failing over.
  11. In the Trunks area of the screen, click
    Add
    .
    If the
    Add
    button is grayed out, there are no trunks on the BIG-IP system.
    The
    Add Trunk to HA Group
    dialog box appears.
  12. From the
    Trunk
    list, select a trunk name.
  13. Using the drop-down list, select a minimum number of active links required for this device to process traffic, which in our example, is
    3
    .
    This value is the minimum number of trunk links that you want to be up in order for
    traffic-group-1
    to remain on its current device. You will assign this HA group to the traffic group later.
  14. For the weight field, type a value such as
    50
    , and for the number of active trunk links that are sufficient to be up for calculating the weight, select a value such as
    3
    .
    For example, if the total number of trunk links is
    4
    , but the value of the
    Sufficient Threshold
    setting is
    3
    and there are only two links currently available, the BIG-IP system calculates the score by multiplying the weight you configured for the trunk by the percentage of links available as compared to the
    sufficient value
    , not to the total number of links. If the weight we configure for the trunk is
    50
    , and 66% of the links are up (2 of 3), then the HA score calculation for the trunk is 50 x 66% = 33.
  15. Click
    Add
    .
    This displays the New HA Group screen and shows the trunk member criteria that must be met to prevent the traffic group from failing over.
  16. Click
    Create HA Group
    .
  17. Log in to each of the remaining devices in the device group and repeat this task, giving each HA group a unique name.
    You can use the same weights and resource criteria within each HA group that you specified for this HA group.
    For example, on
    Device_A
    , if you create
    HA_GroupA_TG1
    and associate it with
    trafffic-group-1
    , then on
    Device_B
    you can create
    HA_GroupB_TG1
    ) and also associate it with
    traffic-group-1
    .
You now have an HA group that the BIG-IP system can use to trigger failover for whatever traffic group instance you assign this HA group to. If you intend to configure the traffic group to select the next-active device based on an HA score, this HA group will calculate an HA score for this device.
After creating an HA group on the local device, you must assign it to a traffic group on the local device.

Enabling an HA group for an existing traffic group

You use this task to associate an HA group with an existing traffic group. You associate an HA group with a traffic group when you want the traffic group to fail over to another device in the device group due to issues with trunk, pool, and/or VIPRION cluster availability. Once a BIG-IP device determines through this association that an active traffic group should fail over, the system chooses the next-active device, according to the failover method that you configure on the traffic group: An ordered list of devices, load-aware failover based on device capacity and traffic load, or the HA score derived from the HA group configuration.
HA groups are not included in config sync operations. For this reason, you must associate a different HA group on every device in the device group for this traffic group. For example, if the device group contains three devices and you want to create an HA group for
traffic-group-1
, you must associate a different HA group for
traffic-group-1
on each of the three devices separately. In a typical device group configuration, the values of the HA group settings on the traffic group will differ on each device.
  1. On the Main tab, click
    Device Management
    Traffic Groups
    .
  2. In the Name column, click the name of a traffic group on the local device.
    This displays the properties of the traffic group.
  3. From the
    HA Group
    list, select an HA group.
  4. Click
    Update
    .
After you perform this task for the same traffic group on each device group member, the BIG-IP system ensures that the traffic group, when active, will fail over to another device when a configured number of trunk links, pool members, or VIPRION cluster members becomes unavailable.

Example of an HA group deployment

This illustration shows three sample devices with two active traffic groups. We've configured both traffic groups to use HA groups to define acceptable criteria for trunk health. Although it's not shown here, we'll assume that
traffic-group-1
and
traffic-group-2
use the HA score and the Preferred Device Order failover methods, respectively, to pick their next-active devices.
In our example, we see that on both
BIG-IP A
and
BIG-IP B
, three of four trunk links are currently up, which meets the minimum criteria specified in the HA groups assigned to
traffic-group-1
and
traffic-group-2
on those devices. This allows each traffic group to stay active on its current device.
Now suppose that the trunk on
BIG_IP A
loses another link. We see that even though
BIG-IP A
is still up,
traffic-group-1
has failed over because
BIG-IP A
no longer meets the HA group criteria for hosting the traffic group: only two of four trunk links are now up on that device.
Because we've configured
traffic-group-1
to use HA scores to select the next-active device, the traffic group fails over to
BIG-IP C
, because this is the device with the most trunk links up and therefore has the highest HA score for hosting this traffic group.
As for
traffic-group-2
, it stays on its current device because
BIG-IP B
still meets the minimum criteria specified in its HA group.