Shell Script to simulate API requests for Load Tests

You can use below shell script to simulate a pre-defined load on an API.

       
#!/bin/bash

#########################################################
# This is simple shell script to simulate API load      #
# for given duration                                    #
# Eg: DURATION=60 and TPS=20, This script will trigger  #
# 20 requests per second for 1 minute.                  #
#########################################################


#define variables

set -x # run in debug mode
DURATION=60 # how long should load be applied ? - in seconds
TPS=20 # number of requests per second
end=$((SECONDS+$DURATION))

#start load
while [ $SECONDS -lt $end ];
do
    for ((i=1;i<=$TPS;i++)); do
        curl -X POST  -H 'Accept: application/json' -H 'Authorization: Bearer xxxxxxxxxxxxx' -H 'Content-Type: application/json' -d '{}' --cacert /path/to/cert/cert.crt -o /dev/null -s -w '%{time_starttransfer}\n' >> response-times.log &
    done
    sleep 1
done
wait

#end load
echo "Load test has been completed" 
       

Download the script from here.

Here while loop is to run this load for given time period
for loop is to fire given number of requests per second
cacert is optional - only used for https request, you can use -k option as well
-o /dev/null is to write the output to empty
-s is to silence the process
-w '%{timestarttransfer}%' is to retrieve the response time. This time will be written to a file
this request will run in background and script will initiate next request.

HTTPS connection using CURL command

When you need to try HTTP connection using CURL command you will return below error,

* Issuer certificate is invalid: 
* NSS error -8156
* Closing connection

Here you need to specify the cert in curl command using --cacert. before that you need to get the cert for your server. You can try below command to get cert.

openssl s_client -connect <host>:<port>

Eg: openssl s_client -connect localhost:8243

Now you can see the ssl certificate. You can extract the text between "-----BEGIN CERTIFICATE-----" and "-----END CERTIFICATE-----" including these two line and save as ssl.crt.

Now you can trigger HTTPS request according to below format

curl -X POST https://localhost:8243/xxxx/v1/test  -d '{}' --cacert /path/to/ssl.crt

How to fix "Could not get lock" Error while apt install

Sometimes we are having below error while trying to install a package using apt install in linux.

sudo apt install default-jre
E: Could not get lock /var/lib/dpkg/lock - open (11: Resource temporarily unavailable)
E: Unable to lock the administration directory (/var/lib/dpkg/), is another process using it?

Reason: some other process is using /var/lib/dpkg/lock

Resolution: 

1. Check whether any other apt install process is running or not. If any process is running wait for that process

2. Reboot OS and try again

3. If above [1] and [2] are not working, the worst option will be removing /var/lib/dpkg/lock file.
     sudo rm /var/lib/dpkg/lock