DevOps Interview Questions

Table of Contents

1. Jenkins
2. AWS
3. Network
4. Linux
5. Ansible
6. Docker
7. Python
8. Prometheus

Jenkins

beginner

• Explain what is Jenkins and what is it used for
• Explain each of the following in the context of nodes:
  • Master
  • Slave
  • Executor
  • Agent
  • Label
• Explain each of the following in context of jobs:
  • Job
  • Build
  • Test
  • Artifacts
• Explain the architecture of Jenkins
• What are the different ways to trigger a build?
• How do you start a build automatically upon a change in a certain repository?
• What is a plugin?
  • What plugins are you using in Jenkins? Which do you consider to most useful?
• Installation questions
  • How to install Jenkins?
  • How to install a plugin?
  • How to install an agent?

Intermediate

• What type of jobs there are? what is the advantage of each type?
• What ways are you familiar with to notify users on build results?

Advanced

• Write a script to remove all the jobs which include the string "REMOVE_ME"

AWS

Global Infrastructure

• Explain the following
  • Availability zone
  • Region
  • Edge location

S3 - beginner questions

• Explain what is S3 and what is it used for
• What is a bucket?
• True or False? a bucket name must be globally unique
• What objects in S3 consists of?
  • Another way to ask it: explain key, value, version id and metadata in context of objects
• Explain data consistency
• Can you host dynamic websites on s3? what about static websites?

CloudFront

• Explain what is CloudFront and what is it used for
• Explain the following
  • Origin
  • Edge location
  • Distribution
• What delivery methods available for the user with CDN?
• True or False? object are cached for the life of TTL

Network

Network questions can be found here

Linux

beginner

• Explain what each of the following commands does and given an example on how to use it

  • ls
  • rm
  • rmdir (can you achieve the same result by using rm?)
  • grep
  • wc
  • df

• How to change the permissions of a file?

• What does the following permissions mean?:

  • 777
  • 644
  • 750

• How to add a new user to the system without providing him the ability to log-in into the system?

• What commands are you using for troubleshooting issues? specifically:

  • Disk issues
  • Memory, CPU issues
  • Networking issues

• What is a Linux kernel module and how do you load a new module?

• What is the different between a soft link and hard link?

hard link is the same file, using the same inode.
soft link is a shortcut to another file, using a different inode.

soft links can be created between different file systems while
hard link can be created only within the same file system.

• How to run a process in the background and why to do that in the first place?

You can achieve that by specifying & at end of the command.
As to Why? since some commands/processes can take a lot of time to finish
execution or run forever

• What signal is used when you run 'kill '?

The default signal is SIGTERM (15). This signal kills
process gracefully which means it allows it to save current
state configuration.

• What signals are you familiar with?

SIGTERM - default signal for terminating a process
SIGHUP - common usage is for reloading configuration
SIGKILL - a signal which cannot caught or ignored

To view all available signals run `kill -l`

Ansible

• Describe each of the following components in Ansible, including the relationship between them:
  • Task
  • Module
  • Play
  • Playbook
  • Role

Task – a call to a specific Ansible module
Module – the actual unit of code executed by Ansible on your own host or a remote host. Modules are indexed by category (database, file, network, …) and also referred as task plugins.

Play – One or more tasks executed on a given host(s)

Playbook – One or more plays. Each play can be executed on the same or different hosts

Role – Ansible roles allows you to group resources based on certain functionality/service such that they can be easily reused. In a role, you have directories for variables, defaults, files, templates, handlers, tasks, and metadata. You can then use the role by simply specifying it in your playbook.

• Write a task to create the directory ‘/tmp/new_directory’

- name: Create a new directory
  file:
      path: "/tmp/new_directory"
      state: directory

• What would be the result of the following play?

---
- name: Print information about my host
  hosts: localhost
  gather_facts: 'no'                                                                                                                                                                           
  tasks:
      - name: Print hostname
        debug:
            msg: "It's me, {{ ansible_hostname }}"

When given a written code, always inspect it thoroughly. If your answer is “this will fail” then you are right. We are using a fact (ansible_hostname), which is a gathered piece of information from the host we are running on. But in this case, we disabled facts gathering (gather_facts: no) so the variable would be undefined which will result in failure.

• Write a playbook to install ‘zlib’ and ‘vim’ on all hosts if the file ‘/tmp/mario’ exists on the system.

---
- hosts: all
  vars:
      mario_file: /tmp/mario
      package_list:
          - 'zlib' 
          - 'vim'
  tasks:
      - name: Check for mario file
        stat:
            path: "{{ mario_file }}"
        register: mario_f

      - name: Install zlib and vim if mario file exists
        become: "yes"
        package:
            name: "{{ item }}"
            state: present
        with_items: "{{ package_list }}"
        when: mario_f.stat.exists

• Write a playbook to deploy the file ‘/tmp/system_info’ on all hosts except for controllers group, with the following content

  I'm <HOSTNAME> and my operating system is <OS>
  

  replace and with the actual data for the specific host you are running on

The playbook to deploy the system_info file

--- 
- name: Deploy /tmp/system_info file
  hosts: all:!controllers
  tasks: 
      - name: Deploy /tmp/system_info
        template:
            src: system_info.j2 
            dest: /tmp/system_info

The content of the system_info.j2 template

# {{ ansible_managed }}
I'm {{ ansible_hostname }} and my operating system is {{ ansible_distribution }

Docker

• What happens when you run docker run hello-world?

Docker CLI passes your request to Docker daemon.
Docker daemon downloads the image from Docker Hub
Docker daemon creates a new container by using the image it downloaded
Docker daemon redirects output from container to Docker CLI which redirects it to the standard output

• How do you run a container?

• What do you see when you run docker ps?

• What docker commit does? when will you use it?

• Explain what is Dockerfile used for and the content of the following Dockerfile

FROM registry.access.redhat.com/rhel7/rhel

RUN yum -y install httpd && yum -y update; yum clean all

EXPOSE 80
ENTRYPOINT [ "/usr/sbin/httpd" ]
CMD [ "-D", "FOREGROUND" ]

Answer:

Use the image 'rhel7/rhel' from the registry 'registry.access.redhat.com` to run httpd.
Befor running it, install the httpd package, update all packages and expose port 80.

Python

beginner

• What data type supported in Python and which of them are mutable? What function can you use to show that a certain data type is mutable?

The mutable data types are:

    List
    Dictionary
    Set
    
The immutable data types are:

    Numbers (int, float, ...)
    String
    Bool
    Tuple

The id function can be used to check if a given variable is mutable or not.

• What is PEP8? Give an example of 5 style guidelines

PEP8 is a list of coding conventions and style guidelines for Python

5 style guidelines:

    1. Limit all lines to a maximum of 79 characters.
    2. Surround top-level function and class definitions with two blank lines.
    3. Use commas when making a tuple of one element
    4. Use spaces (and not tabs) for indentation
    5. Use 4 spaces per indentation level

Intermediate

• What _ is used for in Python?

1. Translation lookup in i18n
2. Hold the result of the last executed expression or statement
3. As a general purpose "throwaway" variable name. For example: x, y, _ = get_data() (x and y are used but since we don't care about third variable, we "threw it away").

• Sort a list of lists by the second item of each nested list

li = [[1, 4], [2, 1], [3, 9], [4, 2], [4, 5]]

sorted(x, key=lambda l: l[1])

• You have the following lists: [{'name': 'Mario', 'food': ['mushrooms', 'goombas']}, {'name': 'Luigi', 'food': ['mushrooms', 'turtles']}] Extract all type of foods. Final output should be: {'mushrooms', 'goombas', 'turtles'}

set([food for bro in x for food in bro['food']])

Prometheus

• Describe the following Prometheus components:
  • Prometheus server
  • Push Gateway
  • Alert Manager

Prometheus server responsible for scraping the storing the data
Push gateway is used for short-lived jobs
Alert manager is responsible for alerts ;)

• What is an exporter? What is it used for?