docker-msftlearn.md

Docker

This section references training from Microsoft Learn.

Docker commands

Follow this nice exercise.

1. Pull an image
   For eg:
   docker pull mcr.microsoft.com/dotnet/samples:aspnetapp
   When we pull an image, Docker stores it locally and makes it available for running it as containers.

2. View images
   For eg:
   docker image list

   REPOSITORY	TAG	IMAGE ID	CREATED	SIZE
   mcr.microsoft.com/dotnet/samples	aspnetapp	6e2737d83726	6 days ago	263MB

   Notice the repository name.

3. Run a docker container
   For eg:

   // Remember the port mapping format as H:C (Host:Container). Host first!
   docker run -p 8080:80 -d mcr.microsoft.com/dotnet/samples:aspnetapp
   

   The command maps port 80 in the container to port 8080 on your computer. So if you visit the page http://localhost:8080, you can see the running web app.

4. View active containers with the docker ps command.
   ps means "process status". It's a shortcut for docker container ls.
   Use a flag if you want to view stopped containers as well.

   For eg:

   CONTAINER ID	IMAGE	COMMAND	CREATED	STATUS	PORTS	NAMES
   57b9587583e3	mcr.microsoft.com/dotnet/core/samples:aspnetapp	"dotnet aspnetapp.dll"	42 seconds ago	Up 41 seconds	0.0.0.0:8080->80/tcp	elegant_ramanujan
   d27071f3ca27	mcr.microsoft.com/dotnet/core/samples:aspnetapp	"dotnet aspnetapp.dll"	5 minutes ago	Up 5 minutes	0.0.0.0:8081->80/tcp	youthful_heisenberg

5. Stop a container
   For eg:
   docker stop elegant_ramanujan

6. Restart a stopped container
   For eg:
   docker start elegant_ramanujan

7. Remove a container
   Typically once a container is stopped, it should also be removed. Removing a container cleans up any resources it leaves behind. Once you remove a container, any changes made within its image filesystem are permanently lost.

   For eg:
   docker rm elegant_ramanujan

   You can't remove a container that's running, but you can force a container to be stopped and removed with the -f flag. Only use this if the app inside the container doesn't need to perform a graceful shutdown.

   For eg:
   docker container rm -f elegant_ramanujan

8. Remove docker images
   For eg:
   docker image rm mcr.microsoft.com/dotnet/core/samples:aspnetapp
   Containers running the image must be terminated before the image can be removed.

Docker Commands cheat sheet

https://docs.docker.com/get-started/docker_cheatsheet.pdf

https://cheat-sheets.nicwortel.nl/docker-cheat-sheet.pdf

Create custom image with a Dockerfile

To create a Docker image containing your application, you'll typically begin by identifying a base image to which you add files and configuration information.

A Dockerfile contains the steps for building a custom Docker image. Follow along this guide at Microsoft Learn.

Also checkout this great blog at docker.com for tips on creating a great image.

Step 1: Clone this sample MSLearn repo to your projects folder:

Ashishs-MacBook-Pro:RiderProjects ashishkhanal$ git clone https://github.com/MicrosoftDocs/mslearn-hotel-reservation-system.git

Step 2: Go into src folder

Ashishs-MacBook-Pro:RiderProjects ashishkhanal$ cd mslearn-hotel-reservation-system/src

Step 3: Create a Dockerfile

Ashishs-MacBook-Pro:src ashishkhanal$ touch Dockerfile

Step 4: Open Dockerfile in Vim

Ashishs-MacBook-Pro:src ashishkhanal$ vim Dockerfile

Hit i to get into insert (write) mode. Make the following changes:

FROM mcr.microsoft.com/dotnet/core/sdk:2.2
WORKDIR /src

# The project files for the web app and the library project are copied to the /src folder in the container.
COPY ["/HotelReservationSystem/HotelReservationSystem.csproj", "HotelReservationSystem/"]
COPY ["/HotelReservationSystemTypes/HotelReservationSystemTypes.csproj", "HotelReservationSystemTypes/"]

# Download the dependencies required by these projects from NuGet.
RUN dotnet restore "HotelReservationSystem/HotelReservationSystem.csproj"

# Copy the source code for the web app to the container. First . comes from the build context, and second . represents container's /src folder. Then build the app. The dll files are written to the /app folder in the container.
COPY . .
WORKDIR "/src/HotelReservationSystem"
RUN dotnet build "HotelReservationSystem.csproj" -c Release -o /app

# dotnet publish command copies the executables for the website to a new folder and removes any interim files. The files in this folder can then be deployed to a website.
RUN dotnet publish "HotelReservationSystem.csproj" -c Release -o /app

EXPOSE 80
# Move to the /app folder containing the published version of the web app.
WORKDIR /app

# When the container runs it should execute the command dotnet HotelReservationSystem.dll
ENTRYPOINT ["dotnet", "HotelReservationSystem.dll"]

Explanation of commands used in Dockerfile:

Command	Action
FROM	Downloads the specified image and creates a new container based on this image.
WORKDIR	Sets the current working directory in the container, used by the subsequent commands.
COPY	Copies files from the host computer to the container. The first argument (.) is a file or folder on the host computer. The second argument (.) specifies the name of the file or folder to act as the destination in the container. In this case, the destination is the current working directory (/src).
RUN	Executes a command in the container. Arguments to the RUN command are command-line commands.
EXPOSE	Creates a configuration in the new image that specifies which ports to open when the container runs. If the container is running a web app, it's common to EXPOSE port 80.
ENTRYPOINT	Specifies the operation the container should run when it starts. In this example, it runs the newly built app. You specify the command you want to run and each of its arguments as a string array.

Step 5: Save and exit

Hit Esc key and type :wq to save (w as in write) and exit the editor.

Step 6: Build the image

This command builds the image and stores it locally.

Ashishs-MacBook-Pro:src ashishkhanal$ docker build -t reservationsystem:v1 .

The docker build command creates a new image by running a Dockerfile.
docker build command creates a container, runs commands in it, then commits the changes to a new image.

-t flag specifies the name of the image to be created. . provides the build context for the source files for the COPY command: the set of files on the host computer needed during the build process. So the first . in the COPY is Ashishs-MacBook-Pro:src ashishkhanal$ which contains following files:

Step 7: Run the image

Give the container a name as reservations.

Ashishs-MacBook-Pro:src ashishkhanal$ docker run -d -p 8080:80 reservationsystem:v1 --name reservations

Step 8: Remove the image

After you're done, you can remove it:

docker rm reservations

Deploy Docker Image to Azure Container Instance

Follow this exercise.

Create Azure Container Registry

1. Create a resource group
   
2. Create container registry
   
3. In the resource menu, under Settings, select Access keys. The Access keys pane for your container registry appears.
4. Enable the Admin user access switch.
   
5. Make a note of the Registry name, Login server, Username, and password.

Tag an Image

In short tags are used in order to identify an image. Also read this for more info.

You push an image from your local computer to Azure Container Registry by using docker push command. Before you push an image, you must create an alias for the image that specifies the repository and tag, that the Azure Container Registry will create (if it doesn't already exist).

A repository in Azure Container Registry is a collection of related Docker images, differentiated by their tags. So when you push an image with a new tag, it's added to the specified repository in the registry.

Tag the current reservationsystem image with the name of our Azure Container Registry.

Ashishs-MacBook-Pro:src ashishkhanal$ docker tag reservationsystem:v1 myregistry5.azurecr.io/reservationsystem:latest

Now check the images again:

Push an Image

1. Sign into Azure Container Registry using docker login <login-server>
   

2. Upload an image using docker push <registry-name>.azurecr.io/reservationsystem:latest

   Ashishs-MacBook-Pro:src ashishkhanal$ docker push myregistry5.azurecr.io/reservationsystem:latest
   

Login Issues if you don't use admin user: https://stackoverflow.com/q/65316558/8644294

Verify an Image

In the resource menu, under Services, select Repositories. The Repositories pane for your container registry appears.

Run an Image

1. Create Container Instances resource
   

   

   On the Advanced tab, set the Restart Policy to Always, and leave all the other settings as is.

   Hit 'Review + Create' -> 'Create'.

   

2. Navigate to the URL: http://container-hotelsystem-eastus-dev.c7bbehfraef3epdq.eastus.azurecontainer.io/api/reservations/1