Jmeter and Docker - docker

Question

I saw some blog posts where people talk about JMeter and Docker. I understand that Docker will be helpful for setting up a container with all the dependencies. But they all run/create the containers in the same host. So ideally all the containers will share the host resources. It is like you run multiple instances of jmeter in the same host. It will not be helpful to generate more load.
When a host has 12GB RAM, I think 1 instance of JMeter with 10GB heap can generate more load than running 10 containers with 1 jmeter instance in each container.
What is the point of running docker here?

Answer 1

I made an automatic solution that can be easily integrated with Jenkins.
The dockerfile should be extended from java8 and add the JMeter build. This Docker image I will call jmeter-base:
FROM java:8
RUN mkdir /jmeter \
&& cd /jmeter/ \
&& wget https://archive.apache.org/dist/jmeter/binaries/apache-jmeter-3.3.tgz \
&& tar -xvzf apache-jmeter-3.3.tgz \
&& rm apache-jmeter-3.3.tgz
ENV JMETER_HOME /jmeter/apache-jmeter-3.3/
# Add Jmeter to the Path
ENV PATH $JMETER_HOME/bin:$PATH
If you want to use a master-slave solution, this is the jmeter master Dockerfile:
FROM jmeter-base
WORKDIR $JMETER_HOME
# Ports to be exposed from the container for JMeter Master
RUN mkdir scripts
EXPOSE 60000
And this is the jmeter slave Dockerfile:
FROM jmeter-base
# Ports to be exposed from the container for JMeter Slaves/Server
EXPOSE 1099 50000
# Application to run on starting the container
ENTRYPOINT $JMETER_HOME/bin/jmeter-server \
-Dserver.rmi.localport=50000 \
-Dserver_port=1099
Now, with the both images, you should execute a script to execute you should know all slave IPs. This script make all the job:
#!/bin/bash
COUNT=${1-1}
docker build -t jmeter-base jmeter-base
docker-compose build && docker-compose up -d && docker-compose scale master=1 slave=$COUNT
SLAVE_IP=$(docker inspect -f '{{.Name}} {{range .NetworkSettings.Networks}}{{.IPAddress}}{{end}}' $(docker ps -aq) | grep slave | awk -F' ' '{print $2}' | tr '\n' ',' | sed 's/.$//')
WDIR=`docker exec -it master /bin/pwd | tr -d '\r'`
mkdir -p results
for filename in scripts/*.jmx; do
NAME=$(basename $filename)
NAME="${NAME%.*}"
eval "docker cp $filename master:$WDIR/scripts/"
eval "docker exec -it master /bin/bash -c 'mkdir $NAME && cd $NAME && ../bin/jmeter -n -t ../$filename -R$SLAVE_IP'"
eval "docker cp master:$WDIR/$NAME results/"
done
docker-compose stop && docker-compose rm -f

Answer 2

I came to understand from this post from a friend of mine that we should not be running multiple docker containers in the same host to generate more load.
http://www.testautomationguru.com/jmeter-distributed-load-testing-using-docker/
Instead the usage of docker here is to quickly setup the jmeter environment.