hackinteach / docker-101

Docker 101

Docker 101

Nuttapat Koonarangsri

Pan Teparak

Last edit : 14 May 2019 @1.44 am

[TOC]

What is Docker

Check it out yourself here

VM || Docker ??

Get start

1. Install Docker CE and Docker Compose
2. See if it works docker version, docker-compose version
3. More verification docker run hello-world

Basic Terminology

Image

​ A class of container. Think it as OS or base technology you want to use.

docker images or docker image ls

Find online images : Docker Hub

Image name: <image name> : <tag/version> ex: python:3.7-alpine

Container

​ A ‘running’ Docker image. Multiple containers can use the same image

docker container ls

Network

docker network ls

Volumes

​ See it like external disk attached to the container

docker volumes or docker volumes ls

Dockerfile

​ A definition of Docker image

Intro to Dockerfile

Path : d1

Dockerfile

FROM python:3.7-alpine # select base image, alpine is cheap
WORKDIR /app # initial path for working dir, create if not exists
RUN pwd # run some script
ADD . . # copy all files from d1/ (host) to /app (container)
RUN ls
CMD python app.py

Build and run it

# Build the image according to Dockerfile, with optional tag (image name)
docker build -t d1 . # notes the "."
# Run the built image with required arguments
docker run d1

---

One more

Path : d2

Dockerfile

FROM python:3.7-alpine
WORKDIR /app
RUN pwd
ADD . .
RUN ls
CMD ["python", "app.py"]

Build and run it

docker build -t d2 .
# now run it as usual
docker run d2 1 2 # expected "Result: 3"

make change in Dockerfile

FROM python:3.7-alpine
WORKDIR /app
RUN pwd
ADD . .
RUN ls
ENTRYPOINT ["python", "app.py"]

now build and re-run it.

---

Connecting from outside world

Path: d3

build and run it : docker build -t d3 . && docker run d3

• now try go to http://localhost:5000/hello/your-name

Try run with docker run -p 5000:5000 d3 or docker run --port 5000:5000 d3

now try again

Task 1

1. Try adding /blah route that just return string blah to screen.
2. build the Dockerfile again
3. see if it works

Now, What can we optimise here ?

From observations, we know that

1. it install req.txt every time you change app.py but we don’t want that to run every time

Solution:

FROM python:3.7-alpine
WORKDIR /app
ADD req.txt .
RUN pip install -r req.txt
ADD . .
CMD gunicorn -b 0.0.0.0:5000 app:app

Now try adding one more route, build, and see the change.

Notes:

you can run Docker in detached/daemon mode by adding -d flag

try: docker run -d d3

and it’ll go background !

---

Using Volumes

Running Database Engine

MySQL Docker

Step 1: Starting a container: docker run -d --name mysql_sample -p 3307:3306 -e MYSQL_ROOT_PASSWORD=milanomilano -e MYSQL_DATABASE=mydb mysql

**Step 2: ** Get into it: docker exec -it mysql_sample mysql -uroot -p, enter password

mysql> CREATE TABLE `mydb`.`user`  (
  `firstname` varchar(255) NULL,
  `lastname` varchar(255) NULL,
  `student_id` int(0) NULL
);
mysql > use mydb;
mysql > show tables;
mysql > exit; # or ctrl + d

Now you have a table user in your database. Now try to remove the container it.

docker stop mysql_sample
docker rm mysql_sample

## OR
docker rm -f mysql_sample

**Step 3: ** start over from Step 1 but with -v ./mysql_data:/var/lib/mysql

now do Step 2 and try to start the Step 1 again, see if your data is still there.

Notes:

You can specify 2 types of volumes: ./dir will use the current directory and create the folder for it, vol_1 will refer to docker volume. For second approach, you can do docker volume create mysql_data and -v mysql_data:/var/lib/mysql. Now with docker volumes you’ll see mysql_data

More on Volumes

path : d3

Goal: Want to see the change for Flask app right away.

We can dogunicorn …… —reload.

1. Run gunicorn locally, make some changes, see what happen
2. build dockerfile
3. run it with -d flag
4. try changing some routes
5. see if it works
6. how to fix ??

SOLUTION

docker run --name d3_vol -v “$(pwd):/app” -d d3

• watch the log docker logs --follow (or -f) --tail 5 d3_vol

• make change to app.py, see the log

• try see the new change.

DockerCompose

What if we have multiple Dockerfile or services that want to run together

Refs

Simple Commands

Docker images