By Esther Vaati, Alibaba Cloud Tech Share Author
In this tutorial, we are going to learn about Docker and how to apply it to website development. We will be deploying a Django application with Docker on an Alibaba Cloud ECS instance.
Docker is a technology that makes it easier to create, deploy, and run applications by using containers. Containers allow developers to package applications with all the components required by the applications and later ship them out as packages. It also makes it possible to get more apps running on the same server.
With Docker, you can be assured of a higher level of security since applications that are running on containers are isolated from each other. In addition, Docker ensures that each container has its own resources and therefore an application will only use the resources that are assigned to it.
Before you begin this guide you'll need the following:
Login to your server using the ssh command.
$ ssh firstname.lastname@example.org
Update Ubuntu packages.
$ sudo apt-get update
Install the latest version of Docker with the following command.
$ sudo apt-get install docker
To verify that Docker has installed correctly run the following command.
$ sudo docker run hello-world
If performed correctly, the above commands should let your instance download a test image and run it in a container.
On an Alibaba Cloud ECS instance, you can use images to create ECS clusters with identical configurations. Similarly, Docker containers have images. Conceptually, they are very similar. Based on the official Docker documentation:
A container image is a lightweight, stand-alone, executable package of a piece of software that includes everything needed to run it: code, runtime, system tools, system libraries, settings.
You can view running containers by running
$ sudo docker ps.
An image, on the other hand, is an inert, immutable, file that's essentially a snapshot of a container. Images are created with the build command, and they'll produce a container when started with the run command.
You can view images by running
$ sudo docker images.
First, let's install Django and Create a Django application.
$ sudo pip install django==1.9 $ django-admin startproject djangoapp
Create a requirements file inside the djangoapp directory and define the dependencies required by the application.
$ cd djangoapp $ nano requirements.txt
Add the following dependencies.
#requirements.txt Django==1.9 gunicorn==19.6.0
Docker has the ability to build images automatically by reading instructions from a Dockerfile. A docker file contains all the commands and instructions that Docker uses to build images.
Let's define some of the basic commands used in a Dockerfile.
Now let’s create a file named Dockerfile.
$ nano Dockerfile
Let's begin by defining all the properties required in a Dockerfile. Define the base image and maintainer name.
# base image FROM python:2.7 # File Author / Maintainer MAINTAINER Esther
Next, copy the application folder inside the container and define the directory where CMD will execute.
# Copy the application folder inside the container ADD . /usr/src/app # set the default directory where CMD will execute WORKDIR /usr/src/app
Finally, set the default command to execute.
CMD exec gunicorn djangoapp.wsgi:application --bind 0.0.0.0:8000 --workers 3
Your final Dockerfile should now look like this.
# set the base image FROM python:2.7 # File Author / Maintainer MAINTAINER Esther #add project files to the usr/src/app folder ADD . /usr/src/app #set directoty where CMD will execute WORKDIR /usr/src/app COPY requirements.txt ./ # Get pip to download and install requirements: RUN pip install --no-cache-dir -r requirements.txt # Expose ports EXPOSE 8000 # default command to execute CMD exec gunicorn djangoapp.wsgi:application --bind 0.0.0.0:8000 --workers 3
Run the following command to build the docker image.
$ sudo docker build -t django_application_image . Sending build context to Docker daemon 12.8kB Step 1/7 : FROM python:2.7 ---> 2863c80c418c Step 2/7 : ADD . /usr/src/app ---> 09b03ff8466e Step 3/7 : WORKDIR /usr/src/app Removing intermediate container a71a3bf6af90 ---> 3186c92adc85 Step 4/7 : COPY requirements.txt ./ ---> 701c0be5e039 Step 5/7 : RUN pip install --no-cache-dir -r requirements.txt ---> Running in ed034f98db74 Collecting Django==1.9 (from -r requirements.txt (line 1)) Downloading Django-1.9-py2.py3-none-any.whl (6.6MB) Collecting gunicorn==19.6.0 (from -r requirements.txt (line 2)) Downloading gunicorn-19.6.0-py2.py3-none-any.whl (114kB) Installing collected packages: Django, gunicorn Successfully installed Django-1.9 gunicorn-19.6.0 Removing intermediate container ed034f98db74 ---> 1ffd08204a07 Step 6/7 : EXPOSE 8000 ---> Running in 987b48e1a4ef Removing intermediate container 987b48e1a4ef ---> ef889d6e8fcb Step 7/7 : CMD exec gunicorn djangoapp.wsgi:application --bind 0.0.0.0:8000 --workers 3 ---> Running in 4d929e361d0f Removing intermediate container 4d929e361d0f ---> c6baca437c64 Successfully built c6baca437c64 Successfully tagged django_application_image:latest
Your built image is now in your machine’s local Docker image registry. You can check your image by running
$ sudo docker images.
REPOSITORY TAG IMAGE ID CREATED SIZE django_application_image latest c6baca437c64 34 minutes ago 702MB
$ sudo docker run -p 8000:8000 -i -t django_application_image [2018-03-25 12:29:08 +0000]  [INFO] Starting gunicorn 19.6.0 [2018-03-25 12:29:08 +0000]  [INFO] Listening at: http://0.0.0.0:8000 [2018-03-25 12:29:08 +0000]  [INFO] Using worker: sync [2018-03-25 12:29:08 +0000]  [INFO] Booting worker with pid: 8 [2018-03-25 12:29:08 +0000]  [INFO] Booting worker with pid: 9 [2018-03-25 12:29:08 +0000]  [INFO] Booting worker with pid: 10
You should see a message that gunicorn is serving your app at http://0.0.0.0:8000. Navigate to your servers IP (ip_address:8000) and you should see the Django welcome page.
To see running containers:
$ sudo docker ps -a CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES 100695b41a0a django_application_image "/bin/sh -c 'exec gu…" 13 seconds ago Exited (0) 4 seconds ago hopeful_easley
Occasionally you might face some challenges when using Docker. The first thing to do when you experience an error is to check Docker logs files as they provide some information on what might have gone wrong.
Docker and other containers are a powerful alternative to traditional virtual machines for application development. To learn more about running containers on Alibaba Cloud, visit the Container Service page.
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