Re: Determining My Own IP address?

2021-04-01 Thread Phil Steitz




On 4/1/21 7:05 PM, Jerry Malcolm wrote:
I am running several clustered Tomcat EC2 instances in an Amazon 
autoscaling group.  These instances come and go based on load and 
failure/restart.  IP addresses are assigned dynamically.  As far I can 
figure, the only determinable difference between the instances is the 
IP address that is assigned to each EC2 when it spins up.


I'm seeing some really weird symptoms at times that seem to indicate 
that the load balancer is not always honoring session affinity.  It 
appears that another server periodically gets sent a request for a 
session that is being handled by a different EC2. The load balancer 
problem, if it exists, is definitely not a tomcat problem.  However, 
in order to figure out what is really happening, I need to be able to 
track and differentiate which server is handling each request.  Inside 
my TC webapp, if I could determine programatically some unique 
identifier for the EC2 running that http request, I could include that 
in my logs.


My question is, is there a way to determine "my own" IP address from 
within a webapp servlet?  Or is there some other way that I can log 
some string or some value that will guarantee to be unique within each 
instance of Tomcat?  I guess another option would be to somehow get 
the tomcat bootup timestamp (from within a servlet) assuming two EC2s 
won't boot at precisely the same instant.  But I don't know a way to 
access the boot timestamp.  Am I missing something more obvious?


You can get this from the getLocalAddr method of the ServletRequest 
object passed to your servlet's doPost/doGet.  See [1].


Phil

https://javaee.github.io/javaee-spec/javadocs/javax/servlet/ServletRequest.html#getLocalAddr


Thx

Jerry


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Determining My Own IP address?

2021-04-01 Thread Jerry Malcolm
I am running several clustered Tomcat EC2 instances in an Amazon 
autoscaling group.  These instances come and go based on load and 
failure/restart.  IP addresses are assigned dynamically.  As far I can 
figure, the only determinable difference between the instances is the IP 
address that is assigned to each EC2 when it spins up.


I'm seeing some really weird symptoms at times that seem to indicate 
that the load balancer is not always honoring session affinity.  It 
appears that another server periodically gets sent a request for a 
session that is being handled by a different EC2. The load balancer 
problem, if it exists, is definitely not a tomcat problem.  However, in 
order to figure out what is really happening, I need to be able to track 
and differentiate which server is handling each request.  Inside my TC 
webapp, if I could determine programatically some unique identifier for 
the EC2 running that http request, I could include that in my logs.


My question is, is there a way to determine "my own" IP address from 
within a webapp servlet?  Or is there some other way that I can log some 
string or some value that will guarantee to be unique within each 
instance of Tomcat?  I guess another option would be to somehow get the 
tomcat bootup timestamp (from within a servlet) assuming two EC2s won't 
boot at precisely the same instant.  But I don't know a way to access 
the boot timestamp.  Am I missing something more obvious?


Thx

Jerry


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