Basic Usage for Docker
2017-11-06 by terryoy, in guides
Just to keep some notes when started to use docker for my development projects.
0. Get Started
For my mac, download the .dmg file from official web site. Then it will run a program with a task icon in the top bar.
After the program has been initialized, you can open a terminal and try a few commands:
# check versions $ docker --version $ docker-compose --version $ docker-machine --version # Current images $ docker images # Running instances $ docker ps
1. First Instance
The docker official Hello World image is small enough, which you can try as your first instance.
$ docker run hello-world
The image does not exist locally currently, but docker will continue to try downloading it and then run it.
Then, you wil see the image locally.
$ docker images REPOSITORY TAG IMAGE ID CREATED SIZE hello-world latest 725dcfab7d63 2 days ago 1.84kB
However, the container for this image is not visible in the list because the process has existed. You need to use a
-a parameter to see it:
$ docker ps -a CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES c32eac048fda hello-world "/hello" 5 minutes ago Exited (0) 5 minutes ago cranky_shaw
2. Server Instance
The Hello World container doesn't do anything. If you want to try something interesting, try the nginx image instead.
$ docker run -d -p 8001:80 --name webserver1 nginx
I choose a different port for the server, just to show how the port mapping is handled. When you check the instance with
docker ps, you can see the image name, instance name, and the port mapping and get the meaning. When the container is up, you can access
http://localhost:8001/ to see the nginx home page.
$ docker ps CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES 6f6ba1d3f285 nginx "nginx -g 'daemon ..." About a minute ago Up About a minute 0.0.0.0:8001->80/tcp webserver1 $ docker images REPOSITORY TAG IMAGE ID CREATED SIZE nginx latest 40960efd7b8f 38 hours ago 108MB hello-world latest 725dcfab7d63 2 days ago 1.84kB
A good point is that you can see how much disk usage every image uses. Now you can stop the service, or remove the unused resources by commands.
# container life cycle methods $ docker stop webserver1 $ docker start webserver1 $ docker restart webserver1 # remove a container $ docker rm webserver1 # remove an image $ docker rmi hello-world
For server instance like Ubuntu, you need an interactive shell to work with it, so the command will be a little bit different:
# start a new container named 'ubuntu' $ docker run --name ubuntu -ti ubuntu-core # run an existing container $ docker container start -i ubuntu # attach console to a server if it has started without interactive environment $ docker container start ubuntu $ docker attach ubuntu # If you want to detach from a server without stopping it # use `ctrl-p ctrl-q` key sequence
You may wonder the file size of each containers, you can checkt it by
docker ps -s. You can see a ubuntu core only uses very small space with the minimal setup.
$ docker ps -s CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES SIZE 070a6e845653 ubuntu "/bin/bash" About an hour ago Up About an hour ubuntu 96.7MB (virtual 219MB) 0200f61f5d65 nginx "nginx -g 'daemon ..." 2 hours ago Up 2 hours 0.0.0.0:5000->80/tcp webserver 2B (virtual 108MB)
3. Other Settings
There are some Docker preferences also mentioned in the Get Started guide, which I should make some notes here:
- Disk Image Location. on Mac, it is stored in a file called “Docker.qcow2” somewhere in ~/Library, and all the containers are store within this image. You can move it somewhere else.
- Experimental features. It is not recommended for production environment, then I wonder why it is turned on by default on Mac.
- *Registry, Configuration, and Certificates for the Daemon *, use it when you needed.
3.1 Download Images by Tags
# Download images/repos from registry $ docker pull <image>:<tag> # Example of getting a core ubuntu system $ docker pull ubuntu:xenial $ docker run --name ubuntu -ti ubuntu
4. Docker for Mac vs Docker Toolbox
Docker Toolbox is also installed by the .dmg installation. The programs include
- Docker for Mac is a Mac native application, you get only one VM, and it is managed by Docker for Mac. The VM is used with a lightweight solution called HyperKit.
- Using Dokcker Toolbox, you can set up one or more VM and manage them.
5. Docker Architecture
The Docker architecture can split into 3 parts:
- Docket Client, the
dockercli tools for user to interact with docker daemon with Docker API.
- Docker Host, the service daemon
dockerdlisten for Docker API request and perform all kinds of management tasks about images, containers, networks, and volumns.
- Docker Registry, a cloud service which stores Docker images, such as Docker Hub and Docker Cloud(both are public registries).
5.1 Docker Objects
- Image, a read-only template with instructions for creating Docker container.
- Container, an instance of an image, with network, file system, etc. attached. You can create, delete, stop, resume containers.
- Service, allow you to scale containers across Docker daemons.
5.2 The Underlying technology
- Namespaces. When you run a container, Docker create a set of namespaces for the container, which provide a layer of isolation. The namespaces includes:
netfor network interfaces
ipcfor interprocess communication
mntfor file system
utsfor kernel and version identifiers (Unix Timeshare System)
- Control Groups. A
cgrouplimits an application to a specific set of resources, and allow Docker Engine to share hardware resources to containers with optionally limits and constraints.
- Container Format. A combination of namespaces, control groups, and UnionFS, packed into a Wrapper. The default format is
6. Developing Apps with Docker
It's easy to setup Docker to deploy with your app. All you need to do is to add a
Dockerfile in your source folder and then build the image. The official example demonstrate how a small flask app is built with Docker.
6.1 First time image
I summarize the steps as below:
- Go to docker hub to find a target python image. It already has all kinds of Dockerfile template for you to copy.
- Create a local copy of the Docker file. Make sure you understand the template and knows what to modify according to your app.
- Write a flask
- Build the docker image and then run with it.
# prepare the source files(...skipped here) $ ls Dockerfile app.py requirements.txt # build the image $ docker build -t slim-flask . # create and run the container $ docker run -p 4000:80 slim-flask * Running on http://0.0.0.0:80/ (Press CTRL+C to quit)
The result will be:
- Only a Dockerfile is added to your source, and others are still remain
- A Python docker image is downloaded, which takes the size of 156MB or 691MB depends on if you choose the “slim” version.
- A flask image for your app is genenrated, which contains the content from the original python image, the pip installed packages from requirements, and your source files. So the size is slightly bigger than the python image.
$ docker images REPOSITORY TAG IMAGE ID CREATED SIZE slim-flask latest 3032f935f40c 10 seconds ago 166MB python slim a79297999298 45 hours ago 156MB
6.2 Create image from a container
However, sometimes you want to make configurations inside a container and want to save it as an image. You can do that:
$ docker container commit [options] CONTAINER [repository:[TAG]] # example $ docker container commit ubuntu ubuntu-image
6.3 Publish docker image
Use it when it is needed.
$ docker login # Log in this CLI session using your Docker credentials $ docker tag <image> username/repository:tag # Tag <image> for upload to registry $ docker push username/repository:tag # Upload tagged image to registry $ docker run username/repository:tag # Run image from a registry
7. Docker mirrors
- Netease, hub-mirror.c.163.com
- USTC, docker.mirrors.ustc.edu.cn
- Daocloud & Alicloud, need registration, and Alicloud needs an dev platform account.