Cool Counter is a simple Sinatra web app. What it does is pretty inconsequential - you increment or decrement a counter, with the count persisted to a Redis database. The real purpose of this repo is to show how to run a simple service-oriented application in 4 ways:

• locally on a Mac
• as Docker containers
• via Docker-Compose
• via Kubernetes (K8s), running on a local multi-node cluster.

This README shows the quick and dirty on installing and running Cool Counter. For a lot more detail on the project, consult LESSONS_LEARNED.

Please set up the following dependencies before attempting to use Cool Counter:

• Git clone this repo (run subsequent commands from within repo)

git clone [email protected]:Adam262/cool-counter.git cool-counter && cd $_

• install Docker Desktop for Mac, a local environment for working with Docker containers

• install ASDF, a system wide version and dependency manager

• install ASDF plugins and packages needed for this app

asdf plugin add kind
asdf plugin add kubectl
asdf plugin add ruby

asdf install

• install Bundler, a package manager for Ruby apps and the gems needed to run this app locally

gem install bundler
bundle install 

Most steps of this app expect the cool-counter Docker image to exist in your local Docker. Build it via below command:

./init.sh build

You will also need to keep rebuilding image if you check out this repo and do work locally. If there are any issues building, it's very helpful to run a Bash shell into a container at the point that the image build failed. You can do this because it is likely the prior images on which image is based succeeded.

# Imagine this step fails
docker build -t cool-counter .

# Find recent image builds (including your build failure)
docker images | head -n 5 

# Exec into bash container for image
docker run -it <your-image-sha> bash

The app runs on localhost:4567

Commands

# Start the app
./init.sh local

# Stop the app
./init.sh local down

The app runs on localhost:4567

Commands

# Start the app
./init.sh docker

# Stop the app
./init.sh docker down

The app runs on localhost:4567

Commands

# Start the app
./init.sh docker-compose

# Stop the app 
./init.sh docker-compose down

The app runs on localhost

Commands

# Start the app
./init.sh k8s

# Stop the app (by deleting namespace and all K8s resources)
./init.sh k8s down

# Stop the app (by additionally deleting cluster)
./init.sh k8s down-cluster

Any init script command can be prefaced with DEBUG=true. This is will cause bash to log commands before executing them, including expanded arguments. For example:

DEBUG=true ./init.sh k8s up

There are a ton of technologies I could apply here. We use them at work, although I haven't necessarily gotten in the weeds for all of them. So could learn a lot.

Some examples:

• Buildpacks. A higher-level abstraction over a Dockerfile
• Prometheus. A monitoring tool. I have an open PR to add monitoring at all steps via Prometheus.
• Helm. The standard chart (package) manager for Kubenetes. For example, there are stable helm charts you can use to install Prometheus to a K8s cluster. The charts follow a common vendor pattern of creating custom K8s resources that work alongside core K8s resources and respond to common K8s commands
• Horizontal Pod Autoscaling. A native K8s feature that would allow the app to scale the number of web containers up and down - automatically - based on the value of a metric (ingested from Prometheus).