siege is an open source program to load test and bechmark web site.
To install siege on Ubuntu/debian, run
apt -y install siege
To generate 250 concurrent users, run
siege -c 250 http://mydomain.com/
To simiulate 100 users with 10 second delay betwen requests
siege -d 10 -c 100 http://mydomain.com/
To simulate real work load, you may need to send traffic to multiple URLs on your web site. You can do this by creating a file with all urls of your web site. Now run
siege -d 10 -c 100 -i -f all-urls.txt
See load