Web-calculator

web-calculator is a web service that allows users to send arithmetic expressions via HTTP and receive their results

Functionality

• Supports addition, subtraction, multiplication, division operations, and expressions in parentheses.
• Expressions can be entered with or without spaces between numbers and operands.
• The calculator accepts positive integers as input.

Requirements

• Python (depends on the linux distribution)

  sudo apt-get update
  sudo apt-get install python3.8

• Pip

  curl https://bootstrap.pypa.io/get-pip.py -o get-pip.py
  python get-pip.py --user

• Ansible (depends on the linux distribution)

  sudo apt-get install ansible

Installation

1. Clone the repository

   git clone https://github.com/eitanas1/web-calculator
   cd web-calculator

2. Configure k8s control-plane's IP and k8s nodes's IP in ansible/inventory.ini file and test the connection

   ansible all -i ansible/inventory.ini -m ping

3. Setup k8s cluster using Ansible playbooks

   ansible-playbook -i ansible/inventory.ini ansible/web-calculator-playbook.yml

4. Run the server from the helm chart

   helm dep up helm
   helm install web-calculator helm

Environment Variables (using Helm chart)

Variable	Description	Default Value
service.type	Service type	ClusterIP
service.port	Service port	8080
env.logLevel	Application log level	INFO
user.username	Dummy application username (only for k8s secret example)	dummy_username
user.password	Dummy application user password (only for k8s secret example)	dummy_password

Security Measurements Implemented

During the CI process security measurements had implemented using those tools:

1. OWASP Dependency-Check - Software Composition Analysis (SCA) tool that attempts to detect publicly disclosed vulnerabilities contained within a project’s dependencies.
2. Anchore Grype - vulnerability scanner for container images and file systems.

Monitoring Tools

In order to monitor the app in k8s cluster, Prometheus and Grafana can be installed:

Prometheus:

kubectl create namespace monitoring
helm repo add prometheus-community https://prometheus-community.github.io/helm-charts
helm repo update
helm install prometheus prometheus-community/prometheus --namespace monitoring

Grafana:

helm repo add grafana https://grafana.github.io/helm-charts
helm repo update
helm install grafana grafana/grafana --namespace monitoring

Challenges faced and solutions applied

• The list of example demo-apps (https://github.com/devopsdemoapps) doesn't contain any apps that are not dockerized. Some of the example demo-apps lack documentation and don't compile or function as expected. To solve it I was looking for other demo-apps that are not dockerized, include sophisticated documentation and can compile and run as expected.
• Providing Jenkins instance on AWS EC2 under the free tier program results in an instance with less resources needed for using different security measurement tools. I was configuring and trying different solutions but some of them couldn't run in this environment. Eventually I picked up OWASP Dependency-Check which is functioning but consuming a lot of data (around 700mb) and Anchore Grype for scanning the docker image for vulnerabilities.
• Ansible is a tool that I never used before so I needed to learn the basics from scratch. Honestly, I found it pretty interesting and efficient.
• The web-calculator app doesn’t require any variables or secrets. In order to demonstrate variables and secrets implementation in the Helm chart, I added a dummy variable and secrets to the Helm chart.

Improvement points

• Jenkins - for cost management purposes, the Jenkins controller (master) is also used as a build executor. For a better stability and performance one or more Jenkins nodes should be added as build executors.
• Application Scalability - autoscaling needed to be configured in order to handle different workloads.
• Secrets management tools - k8s external secrets operator should be added in order to pull secrets dynamically from secrets management tools like HashiCorp Vault, AWS Secret Management etc.
• Test reports - the results of unit tests and security tests should be published as an html report or to an external service.
• Build results - results of every build should be published to a specific commit in github. Any failures should present which specific stage failed and show the test results in case of unit tests or security tests.
• Notifications - notification to the committer (or to a relevant mailing list) should be sent after each build, especially in case of failure.
• Logging - logs should be collected across the k8s cluster and should be published to a central location for log analysis and storage. Log Management Tools such as ELK, Sematext Logs, Datadog, Logz.io etc. should be used.

API

Base URL will be dynamic according to the k8s distribution and the service type. Details will be printed after installing the helm chart. Default base URL: http://localhost:8080

API endpoint	Method	Request Body	Server Response	Response Code
/api/v1/calculate	POST	{"expression": "2 * 2"}	{"result":"4"}	200
/api/v1/calculate	POST	"expression": "2 * 2"	{"error":"Bad request","error_message":"invalid request body"}	400
/api/v1/calculate	GET	{"expression": "2 * 2"}	Method Not Allowed	405
/coffee			I'm a teapot	418
/api/v1/tea			404 page not found	404

Response Codes

• 200 - Successful request
• 400 - Bad request
• 404 - Resource not found
• 405 - Method not allowed
• 422 - Invalid expression (e.g. English letter instead of a number)
• 500 - Internal server error

Usage Examples

For sending POST requests, it's most convenient to use Postman.

1. StatusOK 200

curl 'localhost:8080/api/v1/calculate' \
--header 'Content-Type: application/json' \
--data '{
  "expression": "42 + 5 * 2"
}'

# {"result":52}

curl 'localhost:8080/api/v1/calculate' \
--header 'Content-Type: application/json' \
--data '{
  "expression": "6-8"
}'

# {"result":-2}

curl 'localhost:8080/api/v1/calculate' \
--header 'Content-Type: application/json' \
--data '{
  "expression": "123(3/2)"
}'

# {"result":184.5}

2. Bad Request 400

curl 'localhost/api/v1/calculate' \
--header 'Content-Type: application/json' \
--data '{
  "expression": "2 * 2
}'

# {"error":"Bad request","error_message":"invalid request body"}

3. Unprocessable Entity 422

curl 'localhost:8080/api/v1/calculate' \
--header 'Content-Type: application/json' \
--data '{
  "expression": "cat + 100500"
}'

# {"error":"Expression is not valid","error_message":"invalid characters in expression"}

curl 'localhost:8080/api/v1/calculate' \
--header 'Content-Type: application/json' \
--data '{
  "expression": "()"
}'

# {"error":"Expression is not valid","error_message":"the brackets are empty"}

curl 'localhost:8080/api/v1/calculate' \
--header 'Content-Type: application/json' \
--data '{
  "expression": "1/(2 - 3 + 1)"
}'

# {"error":"Expression is not valid","error_message":"division by zero is not allowed"}

curl 'localhost:8080/api/v1/calculate' \
--header 'Content-Type: application/json' \
--data '{
  "expression": "1 000 000 + 6"
}'

# {"error":"Expression is not valid","error_message":"missing operand"}