A beginner’s guide to Docker — how to create your first Docker application

A beginner’s guide to Docker — how to create your first Docker application

After a short introduction on what Docker is and why to use it, you will be able to create your first application with Docker.

After a short introduction on what Docker is and why to use it, you will be able to create your first application with Docker.

What is Docker?

Docker is a free software developed by Docker Inc. It was presented to the general public on March 13, 2013 and has become since that day a must in the world of IT development.

It allows users to create independent and isolated environments to launch and deploy its applications. These environments are then called containers.

This will let the developer run a container on any machine.

As you can see, with Docker, there are no more dependency or compilation problems. All you have to do is launch your container and your application will launch immediately.

But, is Docker a virtual machine?

Here is one of the most asked question about Docker. The answer is: actually, not quite.

It may look like a virtual machine at first but the functionality is not the same.

Unlike Docker, a virtual machine will include a complete operating system. It will be independent and act like a computer.

Docker will only share the resources of the host machine in order to run its environments.

Why use Docker as a developer?

This tool can really change a developer’s daily life. In order to best answer this question, I have written a non-exhaustive list of the benefits you will find:

  • Docker is fast. Unlike a virtual machine, your application can start in a few seconds and stop just as quickly.
  • Docker is multi-platform. You can launch your container on any system.
  • Containers can be built and destroyed faster than a virtual machine.
  • No more difficulties setting up your working environment. Once your Docker is configured, you will never have to reinstall your dependencies manually again. If you change computers or if an employee joins your company, you only have to give them your configuration.
  • You keep your work-space clean, as each of your environments will be isolated and you can delete them at any time without impacting the rest.
  • It will be easier to deploy your project on your server in order to put it online.

Now let’s create your first application

Now that you know what Docker is, it’s time to create your first application!

The purpose of this short tutorial is to create a Python program that displays a sentence. This program will have to be launched through a Dockerfile.

You will see, it’s not very complicated once you understand the process.

Note: You will not need to install Python on your computer. It will be up to the Docker environment to contain Python in order to execute your code.#### 1. Install Docker on your machine

For Ubuntu:

First, update your packages:

$ sudo apt update

Next, install docker with apt-get:

$ sudo apt-get install docker-ce

Finally, verify that Docker is installed correctly:

$ sudo docker run hello-world

2. Create your project

In order to create your first Docker application, I invite you to create a folder on your computer. It must contain the following two files:

  • A ‘main.py’ file (python file that will contain the code to be executed).
  • A ‘Dockerfile’ file (Docker file that will contain the necessary instructions to create the environment).

Normally you should have this folder architecture:

.
├── Dockerfile
└── main.py
0 directories, 2 files

3. Edit the Python file

You can add the following code to the ‘main.py’ file:

#!/usr/bin/env python3

print("Docker is magic!")

Nothing exceptional, but once you see “Docker is magic!” displayed in your terminal you will know that your Docker is working.

3. Edit the Docker file

Some theory: the first thing to do when you want to create your Dockerfile is to ask yourself what you want to do. Our goal here is to launch Python code.

To do this, our Docker must contain all the dependencies necessary to launch Python. A linux (Ubuntu) with Python installed on it should be enough.

The first step to take when you create a Docker file is to access the DockerHub website. This site contains many pre-designed images to save your time (for example: all images for linux or code languages).

In our case, we will type ‘Python’ in the search bar. The first result is the official image created to execute Python. Perfect, we’ll use it!

# A dockerfile must always start by importing the base image.
# We use the keyword 'FROM' to do that.
# In our example, we want import the python image.
# So we write 'python' for the image name and 'latest' for the version.
FROM python:latest

# In order to launch our python code, we must import it into our image.
# We use the keyword 'ADD' to do that.
# The first parameter 'main.py' is the name of the file on the host.
# The second parameter '/' is the path where to put the file on the image.
# Here we put the file at the image root folder.
ADD main.py /

# We need to define the command to launch when we are going to run the image.
# We use the keyword 'CMD' to do that.
# The following command will execute "python ./main.py".
CMD [ "python", "./main.py" ]

4. Create the Docker image

Once your code is ready and the Dockerfile is written, all you have to do is create your image to contain your application.

$ docker build -t python-test .

The ’-t’ option allows you to define the name of your image. In our case we have chosen ’python-test’ but you can put what you want.

5. Run the Docker image

Once the image is created, your code is ready to be launched.

$ docker run python-test

You need to put the name of your image after ‘docker run’.

There you go, that’s it. You should normally see “Docker is magic!” displayed in your terminal.

Useful commands for Docker

Before I leave you, I have prepared a list of commands that may be useful to you on Docker.

  • List your images.
$ docker image ls

  • Delete a specific image.
$ docker image rm [image name]

  • Delete all existing images.
$ docker image rm $(docker images -a -q)

  • List all existing containers (running and not running).
$ docker ps -a

  • Stop a specific container.
$ docker stop [container name]

  • Stop all running containers.
$ docker stop $(docker ps -a -q)

  • Delete a specific container (only if stopped).
$ docker rm [container name]

  • Delete all containers (only if stopped).
$ docker rm $(docker ps -a -q)

  • Display logs of a container.
$ docker logs [container name]

Before you go…

Thanks for reading! Do not hesitate to give me some feedback to improve my future articles in the comments below.

Mobile App Development Company India | Ecommerce Web Development Company India

Mobile App Development Company India | Ecommerce Web Development Company India

Best Mobile App Development Company India, WebClues Global is one of the leading web and mobile app development company. Our team offers complete IT solutions including Cross-Platform App Development, CMS & E-Commerce, and UI/UX Design.

We are custom eCommerce Development Company working with all types of industry verticals and providing them end-to-end solutions for their eCommerce store development.

Know more about Top E-Commerce Web Development Company

10 docker-compose and docker commands that are useful for active development

10 docker-compose and docker commands that are useful for active development

The following article Lina Rudashevski introduces 10 commands that docker-compose and docker are useful for positive development.

Originally published by Lina Rudashevski at dev.to

Sure you might need other ones but I've found over time that these are the only ones I need or use on a regular basis, and I use Docker and docker-compose regularly for various projects.

1. terminal into the docker container

docker exec -it :container_id bash

You may need to terminal into a container to do things like run tests or apply migrations.

[13:54:41] (master) selfies
🙋 docker ps
CONTAINER ID        IMAGE                  COMMAND                  CREATED             STATUS              PORTS                    NAMES
b5e87b73f6f6        selfies_web            "python manage.py ru…"   2 seconds ago       Up 1 second         0.0.0.0:8000->8000/tcp   selfies_web_1
d8e636ad4805        postgres:10.1-alpine   "docker-entrypoint.s…"   3 seconds ago       Up 2 seconds        0.0.0.0:5432->5432/tcp   selfies_db_1
aeb5cba5a482        redis:latest           "docker-entrypoint.s…"   3 seconds ago       Up 2 seconds        6379/tcp                 selfies_redis_1
[13:54:43] (master) selfies
🙋 docker exec -it b5e87b73f6f6 bash
[email protected]:/selfies# python manage.py makemigrations
No changes detected
[email protected]:/selfies# 

2. run the docker container in debug mode

docker-compose run --service-ports web

If you want to debug your server, this command will let you do it. Otherwise you may get an error if you put a debugger in your code.

[13:56:59] (master) selfies
🙋 docker-compose run --service-ports web
Creating network "selfies_default" with the default driver
Creating selfies_redis_1 ... done
Creating selfies_db_1    ... done
Performing system checks...

System check identified no issues (0 silenced).
July 24, 2019 - 17:57:11
Django version 2.1.7, using settings 'selfies.settings'
Starting ASGI/Channels version 2.2.0 development server at http://0.0.0.0:8000/
Quit the server with CONTROL-C.
Performing system checks...

System check identified no issues (0 silenced).
July 24, 2019 - 18:12:29
Django version 2.1.7, using settings 'selfies.settings'
Starting ASGI/Channels version 2.2.0 development server at http://0.0.0.0:8000/
Quit the server with CONTROL-C.
HTTP OPTIONS /app/users/ 200 [0.01, 172.25.0.1:60046]
> /selfies/app/views/account_views.py(48)post()
-> try:
(Pdb)

3. build the docker container

docker-compose build

This runs everything in the Dockerfile. I usually run this the first time to build the project, and after that only if I add dependencies to my requirements.txt file or change anything within my Dockerfile.

[18:59:42] (master) selfies
// ♥ docker-compose build
db uses an image, skipping
redis uses an image, skipping
Building web
Step 1/7 : FROM python:3.6-stretch
---> 9167692c277e
Step 2/7 : ENV PYTHONUNBUFFERED 1
---> Using cache
---> 0533dfe1c141
Step 3/7 : ENV REDIS_HOST "redis"
---> Using cache
---> c01adb015773
Step 4/7 : RUN mkdir /selfies
---> Using cache
---> e60377d4e9ee
Step 5/7 : WORKDIR /selfies
---> Using cache
---> 9018fb3984b0
Step 6/7 : ADD . /selfies/
---> Using cache
---> 8c6d291d99a7
Step 7/7 : RUN pip install -r requirements.txt
---> Using cache
---> 7caa2f3bf2ac
Successfully built 7caa2f3bf2ac
Successfully tagged selfies_web:latest

4. start the docker container

docker-compose up

This will run your container/s in the terminal and will show the server output

[13:39:32] (master) selfies
🙋 docker-compose up
Creating network "selfies_default" with the default driver
Creating selfies_redis_1 ... done
Creating selfies_db_1 ... done
Creating selfies_web_1 ... done
Attaching to selfies_db_1, selfies_redis_1, selfies_web_1
db_1 | 2019-07-24 17:40:36.069 UTC [1] LOG: listening on IPv4 address "0.0.0.0", port 5432
db_1 | 2019-07-24 17:40:36.069 UTC [1] LOG: listening on IPv6 address "::", port 5432
redis_1 | 1:C 24 Jul 2019 17:40:36.085 # oO0OoO0OoO0Oo Redis is starting oO0OoO0OoO0Oo
redis_1 | 1:C 24 Jul 2019 17:40:36.085 # Redis version=5.0.5, bits=64, commit=00000000, modified=0, pid=1, just started
redis_1 | 1:C 24 Jul 2019 17:40:36.085 # Warning: no config file specified, using the default config. In order to specify a config file use redis-server /path/to/redis.conf
redis_1 | 1:M 24 Jul 2019 17:40:36.086 * Running mode=standalone, port=6379.
redis_1 | 1:M 24 Jul 2019 17:40:36.086 # WARNING: The TCP backlog setting of 511 cannot be enforced because /proc/sys/net/core/somaxconn is set to the lower value of 128.
redis_1 | 1:M 24 Jul 2019 17:40:36.086 # Server initialized
redis_1 | 1:M 24 Jul 2019 17:40:36.086 # WARNING you have Transparent Huge Pages (THP) support enabled in your kernel. This will create latency and memory usage issues with Redis. To fix this issue run the command 'echo never > /sys/kernel/mm/transparent_hugepage/enabled' as root, and add it to your /etc/rc.local in order to retain the setting after a reboot. Redis must be restarted after THP is disabled.
redis_1 | 1:M 24 Jul 2019 17:40:36.086 * Ready to accept connections
db_1 | 2019-07-24 17:40:36.072 UTC [1] LOG: listening on Unix socket "/var/run/postgresql/.s.PGSQL.5432"
db_1 | 2019-07-24 17:40:36.086 UTC [18] LOG: database system was shut down at 2019-07-24 17:39:28 UTC
db_1 | 2019-07-24 17:40:36.090 UTC [1] LOG: database system is ready to accept connections
web_1 | Performing system checks...
web_1 |
web_1 | System check identified no issues (0 silenced).
web_1 | July 24, 2019 - 17:40:38
web_1 | Django version 2.1.7, using settings 'selfies.settings'
web_1 | Starting ASGI/Channels version 2.2.0 development server at http://0.0.0.0:8000/
web_1 | Quit the server with CONTROL-C.

5. start the docker container in the background

docker-compose up -d

This will run the container but in the background so you can continue to type in the terminal. I usually run it this way if I don't really need to see what the server is returning.

[13:31:03] (master) selfies
🙋 docker-compose up -d
Creating network "selfies_default" with the default driver
Creating selfies_db_1 ... done
Creating selfies_redis_1 ... done
Creating selfies_web_1 ... done

6. see all of the docker containers currently running

List of active docker containers which is useful for the CONTAINER ID and to know what you have running.

docker ps

[13:31:10] (master) selfies
🙋 docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
a2b93a900c36 selfies_web "python manage.py ru…" 2 seconds ago Up 1 second 0.0.0.0:8000->8000/tcp selfies_web_1
2d39a1161aa2 postgres:10.1-alpine "docker-entrypoint.s…" 4 seconds ago Up 2 seconds 0.0.0.0:5432->5432/tcp selfies_db_1
62a6f364860e redis:latest "docker-entrypoint.s…" 4 seconds ago Up 2 seconds 6379/tcp selfies_redis_1

7. remove all docker containers in the repository

docker-compose down

I almost always follow this command with docker ps to make sure the containers were successfully removed, out of habit.

[13:37:20] (master) selfies
🙋 docker-compose down
Stopping selfies_web_1 ... done
Stopping selfies_db_1 ... done
Stopping selfies_redis_1 ... done
Removing selfies_web_1 ... done
Removing selfies_db_1 ... done
Removing selfies_redis_1 ... done
Removing network selfies_default

8. remove a specific docker container

docker kill :container_id

The container id is the leftmost column when doing docker ps. I sometimes do this if I need to remove a specific container that I'm not using.

[13:51:43] (master) selfies
🙋 docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
274b1605ca94 selfies_web "python manage.py ru…" 11 minutes ago Up 1 second 0.0.0.0:8000->8000/tcp selfies_web_1
a641f449edfc postgres:10.1-alpine "docker-entrypoint.s…" 11 minutes ago Up 2 seconds 0.0.0.0:5432->5432/tcp selfies_db_1
61b08693e242 redis:latest "docker-entrypoint.s…" 11 minutes ago Up 2 seconds 6379/tcp selfies_redis_1
[13:51:44] (master) selfies
🙋 docker kill 274b1605ca94
274b1605ca94

9. view all of the docker images

You can see all your builds by running this. For me these are either official "images" like redis or python or old builds of my projects. I only occasionally use this, it's not really a part of my daily development.

docker images

[18:28:17] (master) selfies
// ♥ docker images
REPOSITORY TAG IMAGE ID CREATED SIZE
selfies_web latest 4869d063569e 7 days ago 1.32GB
python 3.6-stretch 9167692c277e 11 days ago 936MB
redis latest 598a6f110d01 12 days ago 118MB
<none> <none> 9c4676224e86 2 months ago 1e+03MB
<none> <none> 6c925f68c3a9 2 months ago 929MB
<none> <none> b44ef8ff52f4 2 months ago 929MB
<none> <none> 903b976cd478 2 months ago 1.47GB
<none> <none> f7009c6f0868 2 months ago 1.49GB
<none> <none> 52750c0c3926 2 months ago 1.48GB
<none> <none> 1c509a380925 2 months ago 1.44GB

10. clean out any images, builds, etc., that might be hanging

docker system prune

I only occasionally use this, it's not really a part of my daily development.

[18:18:35] (master) selfies
// ♥ docker system prune
WARNING! This will remove:
- all stopped containers
- all networks not used by at least one container
- all dangling images
- all build cache
Are you sure you want to continue? [y/N] y
Deleted Containers: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Deleted Networks:
selfiesh_default

Originally published by Lina Rudashevski at dev.to

========================================

Thanks for reading :heart: If you liked this post, share it with all of your programming buddies! Follow me on Facebook | Twitter

Learn More

☞ Docker Mastery: The Complete Toolset From a Docker Captain

☞ Docker and Kubernetes: The Complete Guide

☞ Docker for the Absolute Beginner - Hands On - DevOps

☞ Docker Crash Course for busy DevOps and Developers

☞ The Docker for DevOps course: From development to production

☞ Docker for Node.js Projects From a Docker Captain

☞ Docker Certified Associate 2019

☞ Selenium WebDriver with Docker