Before
looking at a way to measure latency to Azure Virtual Machines, let’s see
traditional way to measure latency to any device connected on network /
internet.
I won’t be
talking much about what is latency for which you can Google or Bing, But in
layman language latency is all about the time it takes for a packet to reach
from Node A to Node B and response / acknowledgement of the same packet comes
from Node B to Node A.
Note: Here node refers to any
communicable device.
There are many blogs / website, which completely describes about the term latency so you can refer that.
To begin
with understanding about the latency, below figure describe the traditional way
of measuring latency between the systems.
We use Ping
Command to typically find latency between source and destination by just
pinging to Destination IP Address. In Below Image you can see latency from the
machine (192.168.1.5) I ran ping to destination server with IP Address
192.168.1.4 is 1ms.
Note: Here latency is 1ms (very
less) because the node resides in the same LAN network.
Figure 1: Traditional way to find latency
Ping uses ICMP protocol in background to test the reachability between the nodes, wherein two ICMP types are involved to make this activity successful i.e. Type 0 (Echo Reply) and Type 8 (Echo Request). So this means ICMP Protocol needs to be open between nodes for ping to work properly, and scenario where ICMP protocol is block in firewall, Ping will not be able to provide expected result.
Let’s move
further now to understand how we can find latency of Azure VM’s.
Unlike
previous method to measure the latency of node we used ping utility to get the
latency with the help of ICMP protocol. But here on Azure, every VM is
protected with firewall and it doesn’t support (or allow) inbound ICMP protocol
to reach virtual machines running inside
azure.
Note: Here Azure Endpoint act as
a firewall.
So how we can find out latency other than using ICMP protocol?
If you look
at below image, Endpoint Rule doesn’t allow ICMP for inbound access; But only
TCP or UDP Protocol
Figure 2: Azure Endpoint
So we can
use TCP or UDP Protocol instead ICMP to ping Azure Virtual Machines.
Since default Ping Utility only supports ICMP we would need to use special ping tool which can work on TCP or UDP, and one of such tool I am aware of is PSPing which comes as a part of PSTool in SysInternals.
To Ping
using PSPing on UDP or TCP Port, that port needs to be reachable from Source.
For E.g. If you want to Ping on Port 80, this port needs to be open in Firewall
(Endpoint) and application (Web Server running on Port 80) needs to be running
on Virtual Machine (Destination / Target)
To understand this concept, I have used following Lab to demonstrate the entire concept.
Step 1: Windows Azure
-Here I have
created 1 VM on Azure namely:
a. VM1: SSTest1
(Running Windows 2012 R2)
Figure: VM running on Azure
Step 2: Add
IIS role on VM1
I have
installed this role so that VM will open port for web server and listen on Port
80.I will be using TCP protocol (port 80) to find the latency of Azure VM’s
instead of ICMP protocol, As Azure Endpoint allows only TCP and UDP protocol
for communication.
Step 3: Add
endpoint on VM1 allowing TCP public and private port 80.
Figure: VM1 i.e. SSTEST1 Endpoint configuration
Step 4: Download Tool on source Node
Download PSTools
tool from below mentioned URL, then extract the downloaded package and copy the
psping.exe utility from that package and paste in location C:\Windows\System32
so that you can use the psping utility via cmd prompt.
Link:
http://technet.microsoft.com/en-us/sysinternals/jj729731.aspx
Step 5: Test
the latency
Open cmd
prompt from your computer and type the cmd shown in below image to test the
latency of Azure VM using PSPing.
Figure: psping output
Conclusion: Latency between my Laptop (India, Mumbai) and Azure VM hosted in South East Asia is 103.65ms
