What is Docker and why is it so popular ?
Docker is a container platform which helps in deploying applications as clean and self sufficient containers that eliminates “works on my machine” problems when running of different machines. It helps creating lean containers which Enterprise customers use in delivery software’s faster and more securely to different platforms both Linux and Windows.
But what is a container?
Its a package in which all the dependencies required to run a software is packed, mind you its different from VM because it does not bundle a full operating system, but only the libraries and settings required to make the software work.
Lets see that with an example image from Docker website
So from the above example we can see that VM contains a full OS for an app whereas container contains only the App and its dependencies and running on top of the Docker engine. Which makes it very lean and very quick to spin off.
- Container Image : Its a package with all the dependencies like framework, and the settings needed for the deployment and execution which is needed by the container runtime.
- Container : An instance of an application which is created based on a container image. When you are scaling an application then you add more container by making an instance of the same image.
- Tag : As the name suggest, its a tag or a name you give to the container image to identify itself.
- Dockerfile : A text file giving instructions on how to build a container image.
- Build : Its not usual what we programmers understand when said build meaning compiling the source code, here build means creating a container image with the files provided by following the instructions given in the Dockerfile. You do this with command docker build .
- Docker Engine : The system which lets you create and run container on top of it.
- Repository : Its a pool of related Container images. Same container image may have different variants, some with libraries only some with full SDK’s . Also different variants for different OS (linux or windows).
- Registry : A place which hosts repositories which in turn has different container images. The most common one is Docker Hub . Companies can have their private registry also.
- Docker Trusted Registry (DTR) : Its a registry service which can be installed on premises so that it remains private to the organization. It can be also attached to the Continuous Integration system. Its connect to the LDAP and AD of the organization. More to read here .
- Cluster : A collection of Docker hosts. You can create this cluster using tools like Docker swarm , DC/OS, Kubernetes.
- Orchestrator : A tool to manage Docker cluster and host. It provides command line and graphical interface. It helps in managing the containers and its networks, configurations and also load balancing so that load is distributed to different nodes. Same tool are used for this purpose (Docker swarm, DC/OS, Kubernetes)
Why Docker is so popular?
Docker has been becoming very popular for simple reasons,
- Its the simplest way to test your application in different operating systems
- If it works in a container then you can be sure it works in other system also, or it should work.
- Its faster to spin off a container which make its excellent choice to scale a service.
- Its very light weight which make it very efficient in terms of resource consumption.
- More important if you are willing to manage by yourself , then there is a community edition which is free.
Ok now lets get started.
For this post I will work on Windows 10.
- Install Docker for windows from here
- Install Visual Studio 2017 with .Net Core support (at the time of this post I was using .Net core 1.1)
- Make sure you have Hyper V enabled. Docker needs that.
Lets see some commands to work with Docker
- docker version
- docker images : this should list all the docker images you have it in your system. Initially it will be empty or one dummy image.
- docker pull imageid:version : this will pull the docker image with which we work on. Lets use ubuntu 17.10 for this example. So the command will be
- docker pull ubuntu:17.10
- docker run -it id : Check the below image Basically, I first check for the images, then I use command docker run -it c6 , where -it means interactive that means I want the command prompt to get started for ubuntu else it will run and exit immediately, then c6 is the minimum characters from the IMAGE ID which makes it unique to other image ids. So this is now running ubuntu and you can try ‘cat /etc/*release‘ to check the version of ubuntu. To exit you can just type exit.
Lets build the Asp.Net core app.
- Launch Visual Studio 2017 and create a Asp.Net Core web application and select Web App and un-check the option Enable Docker support. Also I have named the project as DockerExample.
- Change the code of the Home controller a bit so that it looks like this
- Run the app on IIS server, you should see the following output when you click the About page.
- Now lets publish this app to a folder which we can then publish it to Docker. But before that lets create a Dockerfile which will tell how to build the container image. To do that right click on the project and add a text file without file extension .txt, it should be just with name Dockerfile. Add the content of the Dockerfile like below
- In the file the 1st line means that take the container image microsoft/aspnetcore:1.1 , it contains the runtime to run , 3rd line says that copy all the files from the current directory to the host directory, 4th line tell the entry point and which command to use to execute in our case its dotnet command.
- One more important thing, is to set the properties of the Dockerfile to be Copy to output directory always. Right click on the Dockerfile from the visual studio and set the property Copy to Output Directory to be Copy always. So that when we publish, then Dockerfile also gets copied.
- Now lets publish the app, to do that click on
- On the publish window select the Folder option and browse to a folder location, in my case I have used the following location C:\Users\sherry.ummen\Desktop\DockerExample and click publish
- Now lets go to the command prompt and build the docker image. To do that first lets change the directory to be C:\Users\sherry.ummen\Desktop\DockerExample and type the following command. docker build -t sherry/dockerexample:1.0 . . Where option -t is for tag.
- If all is well at your end , then lets run the web app. Type the following command docker run -d -p 8000:80 sherry/dockerexample:1.0 where option -d is to run in background and -p is for port.
- Lets launch the app , open your favorite browser and navigate to 127.0.0.1:8000 and navigate to About page, you should see this
- As you can see that app is running on linux container.
- You can stop the service by typing the following commands
Now the Bonus part. Debugging Asp.Net Core web app running on docker.
- First lets add the Docker support to our project, for that first you would have to delete the Dockerfile from the project, because a new one will be added automatically when we add docker support.
- Now right click on the project and select Add -> Docker Support
- Your solution should look like this
- You will notice that Docker file already created for us.
- Now go to Home controller and add a break point at the beginning of About
- Now click on the run button
- Visual studio will do all the publish and launching the app for you, and if everything has gone well then you should hit the break point, when you navigate to About page.
That’s all! . As you can see Asp.Net Core and Docker works so well and with Visual studio you get its great power of debugging. Can’t wait to explore more.