Running Servers in Containers

INFO 253B: Backend Web Architecture

Kay Ashaolu

What is Docker

  • Docker is an open-source project based on Linux containers
  • Docker enables us to create containers that will run our backend web applications

What does Docker & Containers allow yo to do?

  • Easy to get up and running
  • Easy to find a docker image that you can use right from the box (more on this later)
  • Easy to break down your system into multiple parts, each running in it's own isolated user space

Terminology

  • Docker Engine: like the hypervisor, it's the runtime where docker runs. Manages the containers and builds and run natively on linux
  • Docker Client: Part of the Docker Engine that enables you to communicate with Docker via the terminal
  • Docker Daemon: process that actually executes the commands you send to the docker client 
  • Dockerfile: set of instructions you give docker to build your container. Think of this more as a set of terminal commands

More Terminology

  • Docker Image. Read only templates that is built from a Dockerfile. Used to create Docker Containers
  • Volumes: Disk volumes that enable you to persist and share a container's data. Once a container shuts down, everything within it is deleted. In order to persist data you will need to connect a volume to the container
  • Docker Containers. The actual containers running on your computer. Everything your application needs to run: operating system, application code, system libraries, etc. Built on top of a Docker image

Docker CLI commands

  • docker build: Builds an image from a dockerfile 
  • docker run: builds and runs a container from a dockerfile. If image has not been built, rebuilds image
    • -d: detached, can connect to it via terminal at any time 
    • -i: interactive: be able to "ssh" into your container
    • -t: allows you when ssh to actually send commands
  • docker ps -a: Provides list of containers that have or had running processes in them

Demo: convert quote service to Docker

FROM python:3.9-alpine
COPY . /app
WORKDIR /app
RUN pip install -r requirements.txt
EXPOSE 5000
ENTRYPOINT ["python3"]
CMD ["-m", "flask", "--app", "quote", "run", "--host=0.0.0.0", "--port=5000"]

Demo: convert dictionary service to Docker

# In terminal

# This command build the image and tags it with a name that you can refer to later
docker build -t quote_service_image .

# This command executes an container based on the image built above. It assigns an 
# environment variable "FLASK_APP", and it maps http://localhost:5000 on your host 
# machine to the flask app on port 5000 one he container. 
#
# The EXPOSE keyword in the docker file tells docker
# that the container is communicating on port 5000, but your docker run command must 
# map that port to a port on the host machine
docker run  -dit --name=quote_service_container -p 5050:5000 quote_service_image

# To see and follow the logs of a running container (Ctrl-C to exit)
docker logs -f quote_service_container

# Now check http://localhost:5050 on host computer to see if it worked (note port 5000 in 
# container is mapped to port 5050 on your computer)

Questions?

Running Servers in Containers - Backend Webarch

By kayashaolu

Running Servers in Containers - Backend Webarch

Course Website: https://www.ischool.berkeley.edu/courses/info/253b

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