Determining which packet/update arrived first between two machines
follow this.


Send a request to the load balancer with the body of the request containing the timestamp when it was sent to the server. You can
  easily do this using the DateTime api of your fav language.
After that packet arrives to your backend server residing on your instance (can be a simple node server or a rails server), you can get
  that request, and compare it to the current timestamp. 
You can do this on both the servers and can easily compare which was faster.
I have two separate AWS Virtual Machines set up within a region (different availability zones) both are connected via WebSocket (in Python) to a different load balancer (Cloudfront) of the same host server (also hosted with AWS) and receive frequent small WebSocket payloads - every 5ms.
NB: I do not own the host server I am merely on the receiving end.
Both machines are receiving the same updates and I would like to measure on which machine the updates/payloads/packets are arriving first
In essence I would like to figure out which load balancer is "closer" to the host and so has the least latency overhead in transmitting the signal since my application is highly latency sensitive.
I have tried using the system clock to get timestamps of the data arrival however it is not guaranteed that the two instances have their time synced to an appropriate accuracy.