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.

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

Mysql Load Balancing with Nginx (Ubuntu)

Environment setup:

Mysql master server : 192.168.1.10
Mysql slave server : 192.168.1.12

Nginx server : 192.168.1.14

1. Add Nginx configurations

Add below configuration to nginx main configuration file (/etc/nginx/nginx.conf) just after the http block     

stream {

    upstream mysql_cluster {

        server 192.168.1.10:3306; # node1

        server 192.168.1.12:3306 backup; # node2

    }

    server {

        listen 3306; 

        proxy_pass mysql_cluster;

    }

}

2. Open 3306 port in Nginx server

Since we are using 3306 port, we need to use SELinux and open port privileges

Try below command in Nginx server

sudo semanage port -l | grep http_port_t

check port 3306 is there, if not we can add it by using below command

sudo semanage port -a -t http_port_t  -p tcp 3306 

3. Enable firewall

 If you are using CentOS, you may use below command to enable firewall rules in Nginx server

firewall-cmd --zone=public --add-port=3306/tcp --permanent

firewall-cmd --reload