failover issue between datacenters with GSLB

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1

Ok I have been looking for the best solution for an application requirement.

I have an app that will be living in two datacenters. Each location has 4 servers running. What they want is the application to run 100% of the time in DC1 unless 2 or more servers fail in DC1 and then failover to DC2

I thought this would be rather easy, but I have been unable to find a way to get the VIP to go into a down state if two servers have gone down.

Does anyone have a idea how I could implement this?

Thanks

2

Hello @Brandon_TN

You could use an External Monitor with a custom script to achieve you goal
check this myF5

You could then create a dummy Virtual server with a dummy pool and assign the external monitor to it
And finally use this dummy VS as Dependency for you actual VS in GSLB

3

here is an example

#!/bin/bash
POOL="Your_Pool_name"
THRESHOLD=2

UP_COUNT=$(tmsh show ltm pool $POOL members | grep "Available Members" | awk '{print $4}')

echo "[$(date)] Pool $POOL has $UP_COUNT members up" >> /var/log/pool_monitor.log

if [ "$UP_COUNT" -lt "$THRESHOLD" ]; then
    echo "[$(date)] Pool DOWN: Only $UP_COUNT members up" >> /var/log/pool_monitor.log
    exit 1
else
    echo "[$(date)] Pool UP: $UP_COUNT members up" >> /var/log/pool_monitor.log
    echo "Pool is healthy" 
    exit 0
fi

4

Update GSLB pool configuration with Minimum Active Members to 3. This means the VIP will be marked down if fewer than 3 servers are up (i.e., if 2 or more fail) . The BIG-IP DNS monitors the VIP. If the VIP is down, GTM will failover to DC2.

5

Hi @VishnuGatla is there such an option?
I couldn’t find it.

6

Yes, we have that option under GSLB pool config.

image_342613.png

If we are doing in LTM, K11428303: Priority group assigned to pool members does not take effect

 

7

But in GTM this actually checks available virtual servers not backend servers.

In Ltm also min active members just enable priority group members, does not mark pool as unavailable.

8

Also the old F5 DNS/GTM “Dependency List” option is nice under the Virtual Server https://techdocs.f5.com/kb/en-us/products/big-ip-dns/manuals/product/bigip-dns-concepts-12-0-0/2.html#taskid

9

Hello @Brandon_TN

Did you managed to test it?