High Availability Groups on BIG-IP
High Availability of applications is critical to an organization’s survival.
On BIG-IP, HA Groups is a feature that allows BIG-IP to fail over automatically based not on the health of the BIG-IP system itself but rather on the health of external resources within a traffic group. These external resources include the health and availability of pool members, trunk links, VIPRION cluster members or a combination of all three. This is the only cause of failover that is triggered based on resources outside of the BIG-IP.
An HA group is a configuration object you create and assign to a traffic group for devices in a device group. An HA group defines health criteria for a resource (such as an application server pool) that the traffic group uses. With an HA group, the BIG-IP system can decide whether to keep a traffic group active on its current device or fail over the traffic group to another device when resources such as pool members fall below a certain level.
In this scenario, there are three BIG-IP Devices – A, B, C and each device has two traffic groups on it.
As you can see, for BIG-IP A, traffic-group 1 is active. For BIG-IP B, traffic-group 2 is active and for BIG-IP C, both traffic groups are in a standby state. Attached to traffic-group 1 on BIG-IP A is an HA group which specifies that there needs to be a minimum of 3 pool members out of 4 to be up for traffic-group-1 to remain active on BIG-IP A. Similarly, on BIG-IP B the traffic-group needs a minimum of 3 pool members up out of 4 for this traffic group to stay active on BIG-IP B.
On BIG-IP A, if fewer than 3 members of traffic-group-1 are up, this traffic-group will fail-over.
So let’s say that 2 pool members go down on BIG-IP A. Traffic-group-1 responds by failing-over to the device (BIG-IP) that has the healthiest pool…which in this case is BIG-IP C.
Now we see that traffic-group-1 is active on BIG-IP C.
Achieving the ultimate ‘Five Nines’ of web site availability (around 5 minutes of downtime a year) has been a goal of many organizations since the beginning of the internet era. There are several ways to accomplish this but essentially a few principles apply.
- Eliminate single points of failure by adding redundancy so if one component fails, the entire system still works.
- Have reliable crossover to the duplicate systems so they are ready when needed.
- And have the ability to detect failures as they occur so proper action can be taken.
If the first two are in place, hopefully you never see a failure. But if you do, HA Groups can help.
- Lightboard Lessons: BIG-IP Basic Nomenclature
- Lightboard Lessons: Device Services Clustering
- HA Groups Overview