How to Install and Use Gremlin on CentOS 7¶
Gremlin’s “Resilience as a Service” makes it easy to find weaknesses in your system before they cause problems for your customers. Gremlin is a simple, safe and secure way to use Chaos Engineering to improve system resilience.
Gremlin’s main advantages are:
- Simple: Instead of crafting chaos engineering experiments by hand, you are provided with a range of simple to use attacks that can be automated. Gremlin provides a simple to use Control Panel, API and CLI.
- Safe: All attacks have a halt feature, any experiment can be terminated within seconds. Gremlin provides role-based access controls (RBAC). Companies are the top-level organizational unit in Gremlin. All resources including Clients, Users, and Templates are associated with a Company.
- Secure: Gremlin attacks are generated on the control plane, clients make outbound SSL calls to poll for attacks. Gremlin does not require root privileges to any machines in your infrastructure. Gremlin provides secure command execution, security auditing, multi-factor authentication (MFA) and SAML SSO.
Before you begin this tutorial, you’ll need the following:
- A CentOS 7 server
- A Gremlin account
Step 1 - Installing Gremlin¶
In this step, you’ll install Gremlin.
First, ssh into your host and add the gremlin repo:
ssh username@your_server_ip sudo curl https://rpm.gremlin.com/gremlin.repo -o /etc/yum.repos.d/gremlin.repo
Then install the Gremlin client and daemon:
sudo yum install -y gremlin gremlind
Step 2 - Validating Installation¶
Run the following command to confirm you have all the necessary components installed on your host for Gremlin to function correctly:
You’ll see the output from the Gremlin checks in your console:
Checking resource gremlins ... Checking CPU gremlin ... Attack on cpu_1 completed successfully CPU gremlin OK
Step 3 - Registering with Gremlin¶
You’ll need to register with the Gremlin control plane to create a new Gremlin client session. Gremlin offers tags, a feature allowing you to apply custom labels to a Gremlin client. You can tag more than one Gremlin client with the same label, then use it to view a filtered list of Gremlin clients that share that particular tag. In addition to filtering, the Gremlin Control Panel and API allow you to initiate an action across multiple Gremlin clients with the same tag. Identifying groups of Gremlin clients and administering all of them at once reduces the time required to manage hosts.
Start by initializing Gremlin and assigning tags with the following command. Substitute your desired tag name and tag value for
gremlin init --tag tag_name=tag_value \ --tag tag_name=tag_value \
This will create a new Gremlin client with the tags tag_name and tag_name applied.
Example: Adding tags to a Gremlin client¶
Suppose that you have a collection of hosts and you want to tag them by their service, service-version and service-type.
Initialize Gremlin and assigning tags with the following command:
gremlin init \ --tag service=api \ --tag service-version=1.0.0 \ --tag service-type=http
This will set tags as
If you are using an AWS EC2 instance, Gremlin will also auto-populate tags for
Login to the Gremlin Control Panel using your Company name and sign-on credentials. These details were emailed to you when you signed up to start using Gremlin.
Next click on your name and select Settings in the Gremlin Control Panel.
You will find your Company ID on the left under your company name, then click to generate your Company Secret. We recommend you store your Company Secret somewhere safe since it is only available once. If you lose your Company Secret you will be able to reset it.
On your computer, open your terminal and paste your Company ID and then Company Secret:
Please input your Company ID: Please input your Company Secret:
You are now ready to create attacks using the Gremlin Control Panel.
Step 4 - Creating attacks using the Gremlin Control Panel¶
Login to the Gremlin Control Panel using your Company name and sign-on credentials. These details were emailed to you when you created your Gremlin account.
Example: The “Hello World” of Chaos Engineering (a CPU attack)¶
The “Hello World” of Chaos Engineering is the CPU Resource Attack. To create a CPU Resource Attack select “Resource” and then “CPU” in the dropdown menu.
The CPU Resource Attack will consume CPU resources based on the settings you select. The most popular default settings for a CPU Resource Attack are pre-selected, a default attack will utilize 1 core for 60 seconds. Before you can run the Gremlin attack you will need to click either Exact hosts to run the attack on or click the Random attack option.
Click Exact and select a Gremlin Client in the list.
On your server, run ‘top’ to check the impact of the Gremlin Attack:
$ top top - 06:26:47 up 7 days, 7:00, 1 user, load average: 0.28, 0.07, 0.02 Tasks: 105 total, 1 running, 104 sleeping, 0 stopped, 0 zombie %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 KiB Mem : 1016120 total, 127140 free, 93956 used, 795024 buff/cache KiB Swap: 0 total, 0 free, 0 used. 712192 avail Mem PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 23768 gremlin 20 0 13268 11136 3576 S 99.3 1.1 0:14.05 gremlin 23766 root 20 0 40388 3600 3072 R 0.3 0.4 0:00.03 top 1 root 20 0 37760 5760 3940 S 0.0 0.6 0:13.74 systemd 2 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kthreadd 3 root 20 0 0 0 0 S 0.0 0.0 0:01.28 ksoftirqd/0 5 root 0 -20 0 0 0 S 0.0 0.0 0:00.00 kworker/0:0H 7 root 20 0 0 0 0 S 0.0 0.0 0:06.14 rcu_sched 8 root 20 0 0 0 0 S 0.0 0.0 0:00.00 rcu_bh 9 root rt 0 0 0 0 S 0.0 0.0 0:00.00 migration/0 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 5 - Halting a CPU resource attack using the Gremlin Control Panel¶
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.