Friday, July 01, 2016

More tips and tricks for running Gatling in Docker containers

This post is a continuation of my previous one on "Running Gatling tests in Docker containers via Jenkins". As I continued to set up Jenkins jobs to run Gatling tests, I found the need to separate those tests for different environments - development, staging and production. The initial example I showed contained a single setup, which is not suitable for multiple environments.

Here is my updated Gatling directory structure


Note that I created a separate directory under simulations for each environment (development, staging, production), each with its own simulation files.

I also created a data directory under user-files, because that is the default location for CSV files used by Gatling feeders.

Most importantly, I created a separate configuration directory (staging, production) under gatling/conf, each directory containing its own customized gatling.conf file. I started by copying the gatling-defaults.conf file from GitHub to gatling/conf/staging/gatling.conf and gatling/conf/production/gatling.conf respectively.

Here is what I customized in staging/gatling.conf:

mute = true # When set to true, don't ask for simulation name nor run description
simulations = user-files/simulations/staging

I customized production/gatling.conf in a similar way:

mute = true # When set to true, don't ask for simulation name nor run description
simulations = user-files/simulations/production

Setting mute to true is important because without it, running Gatling in a Docker container was segfaulting while waiting for user input for the simulation ID:

Select simulation id (default is 'gatlingsimulation'). Accepted characters are a-z, A-Z, 0-9, - and _ 
Exception in thread "main" java.lang.NullPointerException
at$Selector.loop$1(Selection.scala:127) at$Selector.askSimulationId(Selection.scala:135) at$Selector.selection(Selection.scala:50) at$.apply(Selection.scala:33) at at at$.start(Gatling.scala:57) at$.fromArgs(Gatling.scala:49) at$.main(Gatling.scala:43) at

The other customization was to point the simulations attribute to the specific staging or production sub-directories.

Since the CSV files containing URLs to be load tested are also environment-specific, I modified the Simulation.scala files to take this into account. I also added 2 JAVA_OPTS variables that can be passed at runtime for HTTP basic authentication. Here is the new Crawl object (compare with the one from my previous post):

object Crawl {
  val feeder = csv("staging-urls.csv").random

  val userName = System.getProperty("username")
  val userPass = System.getProperty("password")

  val crawl = exec(feed(feeder)
    .get("${loc}").basicAuth(userName, userPass)

One more thing is needed: to make Gatling use a specific configuration file instead of its default one, which is conf/gatling.conf. To do that, I set GATLING_CONF as an ENV variable in the Dockerfile, so it can be passed as a 'docker run' command line parameter. Here is the Dockerfile:

# Gatling is a highly capable load testing tool.
# Documentation:
# Cheat sheet:

FROM java:8-jdk-alpine

MAINTAINER Denis Vazhenin

# working directory for gatling

# gating version

# create directory for gatling install
RUN mkdir -p gatling

# install gatling
RUN apk add --update wget && \
  mkdir -p /tmp/downloads && \
  wget -q -O /tmp/downloads/gatling-$ \$GATLING_VERSION/gatling-charts-highcharts-bundle-$ && \
  mkdir -p /tmp/archive && cd /tmp/archive && \
  unzip /tmp/downloads/gatling-$ && \
  mv /tmp/archive/gatling-charts-highcharts-bundle-$GATLING_VERSION/* /opt/gatling/

# change context to gatling directory
WORKDIR  /opt/gatling

# set directories below to be mountable from host
VOLUME ["/opt/gatling/conf", "/opt/gatling/results", "/opt/gatling/user-files"]

# set environment variables
ENV PATH /opt/gatling/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
ENV GATLING_HOME /opt/gatling
ENV GATLING_CONF /opt/gatling/conf


Finally, here is how I invoke 'docker run' to tie everything together:

docker run --rm -v ${WORKSPACE}/gatling/conf:/opt/gatling/conf -v ${WORKSPACE}/gatling/user-files:/opt/gatling/user-files -v ${WORKSPACE}/gatling/results:/opt/gatling/results -e GATLING_CONF="/opt/gatling/conf/staging" -e JAVA_OPTS="-Dusers=$USERS -Dduration=$DURATION -Dusername=myusername -Dpassword=mypass" /PATH/TO/DOCKER/REGISTRY/gatling

Note the GATLING_CONF parameter passed with -e with the value of /opt/gatling/conf/staging. Also note the username and password JAVA_OPTS parameters.

Happy load testing!

1 comment:

Arkka Dhiratara said...

Hi Grig,

I'm very new on load testing using gatling.

Just wondering, do you prefer to run this docker-gatling as a single container on each host/node (we could maximize the throughput for each gatling script) on each host/node,

or it is better to use multiple (hundreds) of containers on each host/node, but with more smaller gatling's load?

how about the saturation?

Modifying EC2 security groups via AWS Lambda functions

One task that comes up again and again is adding, removing or updating source CIDR blocks in various security groups in an EC2 infrastructur...