Simulating vCenter Server Connection Failures with iptables

I was recently testing an application and wanted to see how it would behave if its connection to vCenter Server was interrupted. Would the process auto-recover? Would I need to restart a service? To find out, I simulated a connection failure using the built-in firewall on Photon OS. This type of testing can be helpful when validating resiliency, troubleshooting connection handling, or preparing for real-world outages.

The application was running on a Photon OS appliance, so I checked to see if the native iptables firewall was enabled using the following command:

systemctl status iptables.service

This returned a confirmation that the status was loaded/active, pictured below.

Since the firewall was enabled, I checked its configuration using the command:

iptables --list --line-numbers

This lists all the rules and their associated line numbers in the configuration. At the end of the configuration, I could see a block of OUTBOUND requests, which allow everything (based on rule 7).

Chain OUTPUT (policy DROP)
num  target     prot opt source               destination
1    ACCEPT     tcp  --  anywhere             anywhere             state NEW tcp dpt:https
2    ACCEPT     tcp  --  anywhere             anywhere             state NEW tcp dpt:http
3    ACCEPT     tcp  --  anywhere             anywhere             state NEW tcp dpt:ssh
4    ACCEPT     tcp  --  anywhere             anywhere             state NEW tcp dpt:https
5    ACCEPT     tcp  --  anywhere             anywhere             state NEW tcp dpt:http
6    ACCEPT     tcp  --  anywhere             anywhere             state NEW tcp dpt:ssh
7    ACCEPT     all  --  anywhere             anywhere
8    ACCEPT     icmp --  anywhere             anywhere             icmp echo-reply
9    ACCEPT     icmp --  anywhere             anywhere             icmp echo-reply

For my testing, I only needed to create a rule above number 7 that would DROP the requests to the specific vCenter Server my request was going to. I waited for the application to start, then added this firewall rule to drop requests to the vCenter Server, effectively simulating a network interruption:

iptables -I OUTPUT 7 -d 192.168.127.40 -j DROP

Caution: these changes are meant to be temporary and should only be used in test environments.

I then ran the same iptables --list --line-numbers command and confirmed that rule 7 was now my DROP entry and the previous rule 7 (that allowed all traffic) shifted down to rule number 8.

Finally, after testing, I could remove the rule:

iptables -D OUTPUT 7

Conclusion

Using iptables makes it easy to simulate a loss of connectivity to vCenter (or any other target system) without touching physical network infrastructure. This approach is lightweight, repeatable, and useful for testing application resiliency or recovery processes. Just remember that iptables changes made this way are not persistent across reboots, so they’re ideal for temporary testing in a lab or non-production environment.