Configure HA Groups on BIG-IP
Last week we talked about how HA Groups work on BIG-IP and this week we’ll look at how to configure HA Groupson BIG-IP. To recap, 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. First, some prerequisites: Basic Setup: Each BIG-IP (v13) is licensed, provisioned and configured to run BIG-IP LTM HA Configuration: All BIG-IP devices are members of a sync-failover device group and synced Each BIG-IP has a unique virtual server with a unique server pool assigned to it All virtual addresses are associated with traffic-group-1 To the BIG-IP GUI! First you go to System>High Availability>HA Group List>and then click the Create button. The first thing is to name the group. Give it a detailed name to indicate the object group type, the device it pertains to and the traffic group it pertains to. In this case, we’ll call it ‘ha_group_deviceA_tg1.’ Next, we’ll click Add in the Pools area under Health Conditions and add the pool for BIG-IP A to the HA Group which we’ve already created. We then move on to the minimum member count. The minimum member count is members that need to be up for traffic-group-1 to remain active on BIG-IP A. In this case, we want 3 out of 4 members to be up. If that number falls below 3, the BIG-IP will automatically fail the traffic group over to another device in the device group. Next is HA Score and this is the sufficient threshold which is the number of up pool members you want to represent a full health score. In this case, we’ll choose 4. So if 4 pool members are up then it is considered to have a full health score. If fewer than 4 members are up, then this health score would be lower. We’ll give it a default weight of 10 since 10 represents the full HA score for BIG-IP A. We’re going to say that all 4 members need to be active in the group in order for BIG-IP to give BIG-IP A an HA score of 10. And we click Add. We’ll then see a summary of the health conditions we just specified including the minimum member count and sufficient member count. Then click Create HA Group. Next, we go to Device Management>Traffic Groups>and click on traffic-group-1. Now, we’ll associate this new HA Group with traffic-group-1. Go to the HA Group setting and select the new HA Group from the drop-down list. And then select the Failover Method to Device with the Best HA Score. Click Save. Now we do the same thing for BIG-IP B. So again, go to System>High Availability>HA Group List>and then click the Create button. Give it a special name, click Add in the Pools area and select the pool you’ve already created for BIG-IP B. Again, for our situation, we’ll specify a minimum of 3 members to be up if traffic-group-1 is active on BIG-IP B. This minimum number does not have to be the same as the other HA Group, but it is for this example. Again, a default weight of 10 in the HA Score for all pool members. Click Add and then Create HA Group for BIG-IP B. And then, Device Management>Traffic Groups> and click traffic-group-1. Choose BIG-IP B’s HA Group and select the same Failover method as BIG-IP A – Based on HA Score. Click Save. Lastly, you would create another HA Group on BIG-IP C as we’ve done on BIG-IP A and BIG-IP B. Once that happens, you’ll have the same set up as this: As you can see, BIG-IP A has lost another pool member causing traffic-group-1 to failover and the BIG-IP software has chosen BIG-IP C as the next active device to host the traffic group because BIG-IP C has the highest HA Score based on the health of its pool. Thanks to our TechPubs group for the basis of this article and check out a video demo here. psHigh 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. ps Related: Lightboard Lessons: BIG-IP Basic Nomenclature Lightboard Lessons: Device Services Clustering HA Groups Overview
