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Friday, October 23, 2015

SSH and screen command and JMeter

We all know how useful JMeter distributed testing is when it comes to generating how amount of load from multiple machines. This requires certain ports on remote test agent to be opened so that a centralized JMeter server could talk to them and execute test.
Given the inability to get port opened on aws test agents, I could not employ JMeter distributed testing. Hence I resorted to looping through SSH connection and screen command to execute load test on remote machine. Not an ideal solution but far better than logging in to each test agent and starting test manually.

If you never used screen command then Matt has a quick tutorial on it.
I have load test machine image, it is child’s play to bring up load test agent with exactly same configuration on AWS.

This is how for loop looks like -

for server in ip1 ip2 ip3; do
   ssh -tA <you ssh command here> @$server 'bash -s' <
done is shell script which is executed on each ip address mentioned above. you don’t need to copy it to remote server to run it. looks like -

# delete existing screen (could be residual from last test)
for session in $(screen -ls | grep -o '[0-9]\{6\}')
    screen -S "${session}" -X quit;

screen -d -m -S loadtest; screen -S loadtest -X stuff "cd perftest/s2s/;rm testresult*;./;"`echo -ne '\015'`;

Herein -
<screen -d -m -S loadtest> creates screen with name “loadtest” and detaches from it

<screen -S loadtest -X stuff> is used to pass subsequent command to screen “loadtest” which we created above

<"cd perftest/s2s/;rm testresult*;./;C-a d" > does following -
  • navigate to required directory,
  • remove the last test results (my test result files are of format testresult_TimeStamp),
  • ./runs2s runs the load test (that is is running JMeter load test from command line) and
  • `echo -ne '\015'` simulates hitting enter key

but why not create session directly using <screen -s loadtest> and send command to it instead of creating a session, detaching from it and then sending commands to detached session ?
I tried it and failed with the error specified here. Solution specified in the post did not work for me and I had to created a detached screen session and send commands to it.

Why use and not send command along with ssh as specified here?
I tried this too, but failed on syntax. There are single and double quotes in and escaping did not work. If you are able to send it along with ssh command then please post your comment here.

One test execution is over then I use another ssh loop to bring test results to my machine. Which I merge to one file and begin analysis. ssh loop is pretty simple looks as -

for server in ip1 ip2 ip3;
   scp -rp $server:perftest/s2s/testresult.* .

That’s all :-)
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