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GCP ILB Issue Targets Not Healthy

I ran into an issue with Google Compute Engine TCP internal load balancer. The targets are unhealthy although all configs were correct installed. At one time the targets were working, but somehow they became unhealthy. In the end, 3 things needed to be checked.

  1. Make sure GCP’s guest environment is installed.
  2. Add the internal load balancer VIP address to the network properties.
  3. Add route via cmd. “route ADD VIP MASK 255.255.255.255”

You will need to change the server’s IP from DHCP to static to add ILB VIP.

Windows Route Add

Here’s how to add a route in Windows. Open CMD as Administrator.

route add 10.10.10.10 mask 255.255.255.0 10.10.10.254

To make it persistent, add -p.

route add 10.10.10.10 mask 255.255.255.0 10.10.10.254

To display. Specifies IP 4 only.

route print -4

GCP Load Balancer Local Routing Table

Test if the GCP Load Balancer is working by sending a curl command from the backend VM.

Assume the load balancer IP address is 10.1.2.99, and the VM is called vm-a1.

curl http://10.1.2.99

The end result is …

Page served from: vm-a1

Make sure there’s an entry in the local table that matches the IP of the load balancer.

ip route show table local | grep 10.1.2.99

If not, add it.

ip route add to local 10.1.2.99/32 dev eth0 proto 66

Documentation