tl;dr download this gist as a zip, unpack and run `docker-compose up` (need to have docker installed)

README.md

Run a container:

docker run ruby:2.7

# run and open bash shell
# --rm will remove the container when done instead of keeping it around
# you can clear any lingering containers with a `docker system prune`
docker run -it --rm ruby:2.7 bash

# mount files onto the container (updates to local files will reflect on the container)
docker run -it --rm -v $PWD:/app  ruby:2.7 bash

# map port from container to host
docker run -it --rm -p 4567:4567 -v $PWD:/app  ruby:2.7 bash

Check on running containers:

# list running container
docker ps

# check resource utilization of running containers
docker stats

# connect to a running container
docker exec -it <image-name-or-id> bash

Orchestrating with docker-compose: NOTE: all docker-compose commands need to be run in a directory that has a docker-compose.yml file (or pass the -f flag)

# build all services
docker-compose build

# build a specific service's container
docker-compose build <service-name>

# start and stop services
docker-compose start
docker-compose stop

# create / remove services (will do the start/stop; prefer these if you want to get a clean slate)
# up will build if containers have not been built before, run docker-compose build if you need to rebuild
docker-compose up
docker-compose down

# restart all services or a particular service
docker-compose restart
docker-compose restart <service-name>

# list running container that are orchestrated by just this compose file
docker-compose ps

# get logs (stdout & stderr) from all containers
docker-compose logs

Docker and docker-compose sample

Ruby web app (web.rb):

require 'sinatra'
require 'redis'

get '/hello/:name?' do
  "Hello #{params["name"]}!"
end

get '/count' do
  redis = Redis.new(host: "redis")
  redis.incr("count")
  puts "#{redis.get("count")}"
  "#{redis.get("count")}"
end

Dockerfile for building a container image:

FROM ruby:2.7

RUN gem install sinatra redis

WORKDIR /app

COPY . .

CMD ["ruby", "web.rb", "-o", "0.0.0.0"]

Config for spinning up the ruby container image & redis using docker-compose.yml

version: '3'
services:
  web:
    build: ./
    ports:
      - "4567:4567"
    volumes:
        - ${PWD}:/app
  redis:
    image: "redis:5"

Place all 3 files in a directory and run:

docker-compose up

This will pull down the necessary images (ruby & redis), build the web container and start the web and redis services. If all goes well, the ruby app should be accessible at 4567 on your host machine:

https://localhost:4567/hello/:name and https://localhost:4567/count

Try this at the terminal (or open the urls in a browser):

At the terminal

curl -i 'https://localhost:4567/hello/world'
curl -i 'https://localhost:4567/hello/abc'

curl -i 'https://localhost:4567/count'

docker-compose.yml

version: '3'
services:
  web:
    build: ./
    ports:
      - "4567:4567"
    volumes:
        - ${PWD}:/app
  redis:
    image: "redis:5"

Dockerfile

FROM ruby:2.7

RUN gem install sinatra redis

WORKDIR /app

COPY . .

CMD ["ruby", "web.rb", "-o", "0.0.0.0"]

web.rb

require 'sinatra'
require 'redis'

redis = Redis.new(host: "redis")

get '/hello/:name?' do
  "Hello #{params["name"]}!!\n"
end

get '/count' do
  redis.incr("count")
  "#{redis.get("count")}\n"
end