How about bring the secondary VCE up?
Assume the primary VCE is up and the secondary VCE is off. When we power on the secondary VCE, during the boot up, the LAN interface with secondary IP will be initialized and being bring up, which it can cause the HaVip sending the traffic to the secondary VCE instead. After the secondary VCE is completely boot up, the /opt/vc/bin/failover_exp.py gets kick start, it then shutdown the LAN interface, at this point the environment becomes stable. In addition, the python script cannot be very aggressive to shutdown the LAN interface right away when it can ping the primary VCE WAN IP, because it can be in the scenario the primary VCE is also initializing.
Thus, when the primary VCE is up and we bring up the secondary VCE, there will be a few minutes like a “chaos period” which the connectivity going on and off. If the administrator want to avoid this, the administrator can consider unbind the secondary VCE ENI from the HaVip first. After power up the secondary VCE and wait for enough time, bind the secondary VCE ENI back to the HaVip.
Possible further enhancements
There are some enhancements can be made:
- Add job to monitor the python script. At the moment, the /opt/vc/bin/failover_exp.py running in a forever loop. But if somehow the script gets terminated, then there is no process to bring the script up again.
- A better checking mechanism of the primary status. Currently, the script just check the primary VCE status by pinging the WAN interface IP address, this cannot reflect the primary VCE is really functioning, further enhancement can be consider to perform a more precise checking.
And certainly, if you plan to use this python script, you can feel free to do any enhancement or tuning on it.
Conclusion
This failover_exp.py together with Alibaba Cloud HaVip, makes Velocloud virtual edge failover possible, without the need of an external VM/function to run a script, and it also does not touch the VPC route table. I hope this script is helpful when you need VCE having HA ability in Alibaba Cloud.