How to Install and Use Gremlin on CentOS 7

Tammy Butow

Principal SRE

Last Updated: July 14, 2020

Categories: Chaos Engineering

Introduction

This tutorial will walkthrough how to install Gremlin on CentOS 7 and perform a Chaos Engineering experiment using a Gremlin CPU attack.

Prerequisites

Before you begin this tutorial, you'll need the following:

• A CentOS 7 server
• A Gremlin account (request a free trial)

Step 1 - Getting Team Credentials

After you have created your Gremlin account, you will need to find your Gremlin Daemon credentials. Login to the Gremlin App using your Company name and sign-on credentials. These were emailed to you when you signed up to start using Gremlin.

Navigate to Team Settings from the user icon in the upper right hand corner.

Click on the Configuration tab. Make a note of your Gremlin Team ID.

Press the Reset button next to Secret Key. A prompt will appear once the Secret Key has been set. Copy the key and keep it for future installation as this information will NOT be displayed again.

Step 2 - Installing the Gremlin Daemon and CLI

First, add the Gremlin RPM repository:

1# Add the Gremlin repo
2sudo curl https://rpm.gremlin.com/gremlin.repo -o /etc/yum.repos.d/gremlin.repo

Then install the Gremlin daemon and CLI:

1# Install Gremlin agent and daemon
2sudo yum install -y gremlin gremlind

Then initialize Gremlin and follow the prompts:

1gremlin init
2Please input your Team ID:
31c485fb2-d288-5a7e-a6c3-070be181d66a
4Please input your Team Secret:(Text output will not appear)
5
6Using 1c485fb2-d288-5a7e-a6c3-070be181d66a for Team Id
7Using 172.31.31.231 for Gremlin identifier

You are now ready to create attacks using the Gremlin App.

Step 3 - Creating attacks using the Gremlin App

You can use the Gremlin App or the Gremlin API to trigger Gremlin attacks. You can view the available range of Gremlin Attacks in Gremlin Help. For this example, we'll be focusing on the Gremlin App

To start an attack from the Gremlin App, select New Attack from the Attacks page.

Under Choose Host to target, select Exact to select the specific host that we had set up in step 2. We know that this is the host because the IP matches from the last output of Gremlin init

The next step is Choose a Gremlin. It is here that we'll select the attack that we want to perform against the host.

The Hello World of Chaos Engineering is the CPU Resource Attack. Once we have set all the parameters of the attack, click Unleash Gremlin to start the attack.

Your attack will begin to run, you will be able to view its progress via Gremlin Attacks in the Gremlin App.

On your server, run top to check the impact of the Gremlin Attack:

1top
2
3top - 06:26:47 up 7 days,  7:00,  1 user,  load average: 0.28, 0.07, 0.02
4Tasks: 105 total,   1 running, 104 sleeping,   0 stopped,   0 zombie
5%Cpu(s): 79.7 us, 20.3 sy,  0.0 ni,  0.0 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
6KiB Mem :  1016120 total,   127140 free,    93956 used,   795024 buff/cache
7KiB Swap:        0 total,        0 free,        0 used.   712192 avail Mem
8
9  PID USER      PR  NI    VIRT    RES    SHR S %CPU %MEM     TIME+ COMMAND
1023768 gremlin   20   0   13268  11136   3576 S 99.3  1.1   0:14.05 gremlin
1123766 root      20   0   40388   3600   3072 R  0.3  0.4   0:00.03 top
12    1 root      20   0   37760   5760   3940 S  0.0  0.6   0:13.74 systemd
13    2 root      20   0       0      0      0 S  0.0  0.0   0:00.00 kthreadd
14    3 root      20   0       0      0      0 S  0.0  0.0   0:01.28 ksoftirqd/0
15    5 root       0 -20       0      0      0 S  0.0  0.0   0:00.00 kworker/0:0H
16    7 root      20   0       0      0      0 S  0.0  0.0   0:06.14 rcu_sched
17    8 root      20   0       0      0      0 S  0.0  0.0   0:00.00 rcu_bh
18    9 root      rt   0       0      0      0 S  0.0  0.0   0:00.00 migration/0
19   10 root      rt   0       0      0      0 S  0.0  0.0   0:04.09 watchdog/0

When your attack is complete it will move to Completed Attacks.

Step 4 - Halting a CPU resource attack using the Gremlin App

You can stop a Gremlin Attack at anytime using the Gremlin App. Navigate to Gremlin Attacks and click on the halt button.

Conclusion

You've installed Gremlin on a server running CentOS 7 and validated that Gremlin works by running the Hello World of Chaos Engineering, the CPU Resource attack. You now possess tools that make it possible for you to explore additional Gremlin Attacks including attacks that impact State and Network.

Gremlin's Developer Guide is a great resource and reference for using Gremlin to do Chaos Engineering. You can also explore the Gremlin Blog for more information on how to use Chaos Engineering with your application infrastructure.