Step by step: Scale ASP.NET Core with Docker Swarm

A few weeks ago I posted Step by step: ASP.NET Core on Docker were I showed how to build and run a Docker image with an ASP.NET Core application.

Today I bring you: Step by step: Scale ASP.NET Core with Docker Swarm so you can scale out or in the same application.

Assuming you have Docker 1.12 or later installed and running, follow this steps:

Create a dockerfile

On your Docker box create a dockerfile with the following contents

    # We use the microsoft/dotnet image as a starting point.
    FROM microsoft/dotnet

    # Install git
    RUN apt-get install git -y

    # Create a folder to clone our source code 
    RUN mkdir repositories

    # Set our working folder
    WORKDIR repositories

    # Clone the source code
    RUN git clone https://github.com/cmendible/aspnet-core-helloworld.git

    # Set our working folder
    WORKDIR aspnet-core-helloworld/src/dotnetstarter

    # Expose port 5000 for the application.    
    EXPOSE 5000

    # Restore nuget packages
    RUN dotnet restore

    # Start the application using dotnet!!!
    ENTRYPOINT dotnet run

Create a Docker image

With the dockerfile in place run the following command

sudo docker build -t hello_world .

Now you have an image named hello_world with all the dependencies and code needed to run the sample.

Initialize a Swarm

Initialize Docker Swarm.

docker swarm init

Create a Docker Service

Now that you have setup everything use the following command to create a service named hello_service based on the hello_world image and start it

docker service create --name hello_service --publish 5000:5000 hello_world

Wait a few seconds and navigate to http://localhost:5000 and you should be able to reach the web application.

If you want to learn more about Docker services, start here: Service Create/

Scale up your application

Let’s scale your service up to 3 instances with the following command

docker service scale hello_service=3

If you want to see how many replicas your service is running issue the following command:

docker service ls

Note that it takes some seconds before all new replicas start.

Scale down your application

Let’s scale your service down to 1 instance with the following command

docker service scale hello_service=1

Optional: Remove the service

If you are don’t want the service anymore, remove it from the Swarm with the following command

docker service rm hello_service

You can get a copy of the docker file here: https://github.com/cmendible/dotnetcore.samples/tree/main/docker.helloworld

Hope it helps!

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