Docker basics for Amazon ECS

To install Docker on an Amazon EC2 instance

1. Launch an instance with the Amazon Linux 2 or Amazon Linux AMI. For more information, see Launching an instance in the Amazon EC2 User Guide for Linux Instances.

2. Connect to your instance. For more information, see Connect to your Linux instance in the Amazon EC2 User Guide for Linux Instances.

3. Update the installed packages and package cache on your instance.

   sudo yum update -y

4. Install the most recent Docker Engine package.

   Amazon Linux 2

   sudo amazon-linux-extras install docker

   Amazon Linux.

   sudo yum install docker

5. Start the Docker service.

   sudo service docker start

6. Add the ec2-user to the docker group so you can execute Docker commands without using sudo.

   sudo usermod -a -G docker ec2-user

7. Log out and log back in again to pick up the new docker group permissions. You can accomplish this by closing your current SSH terminal window and reconnecting to your instance in a new one. Your new SSH session will have the appropriate docker group permissions.

8. Verify that the ec2-user can run Docker commands without sudo.

   docker info

   Note

   In some cases, you may need to reboot your instance to provide permissions for the ec2-user to access the Docker daemon. Try rebooting your instance if you see the following error:

   Cannot connect to the Docker daemon. Is the docker daemon running on this host?

To create a Docker image of a simple web application

1. Create a file called Dockerfile. A Dockerfile is a manifest that describes the base image to use for your Docker image and what you want installed and running on it. For more information about Dockerfiles, go to the Dockerfile Reference.

   touch Dockerfile

2. Edit the Dockerfile you just created and add the following content.

   FROM ubuntu:18.04
   
   # Install dependencies
   RUN apt-get update && \
    apt-get -y install apache2
   
   # Install apache and write hello world message
   RUN echo 'Hello World!' > /var/www/html/index.html
   
   # Configure apache
   RUN echo '. /etc/apache2/envvars' > /root/run_apache.sh && \
    echo 'mkdir -p /var/run/apache2' >> /root/run_apache.sh && \
    echo 'mkdir -p /var/lock/apache2' >> /root/run_apache.sh && \ 
    echo '/usr/sbin/apache2 -D FOREGROUND' >> /root/run_apache.sh && \ 
    chmod 755 /root/run_apache.sh
   
   EXPOSE 80
   
   CMD /root/run_apache.sh

   This Dockerfile uses the Ubuntu 18.04 image. The RUN instructions update the package caches, install some software packages for the web server, and then write the "Hello World!" content to the web server's document root. The EXPOSE instruction exposes port 80 on the container, and the CMD instruction starts the web server.

3. Build the Docker image from your Dockerfile.

   Note

   Some versions of Docker may require the full path to your Dockerfile in the following command, instead of the relative path shown below.

   docker build -t hello-world .

4. Run docker images to verify that the image was created correctly.

   docker images --filter reference=hello-world

   Output:

   REPOSITORY          TAG                 IMAGE ID            CREATED             SIZE
   hello-world         latest              e9ffedc8c286        4 minutes ago       241MB

5. Run the newly built image. The -p 80:80 option maps the exposed port 80 on the container to port 80 on the host system. For more information about docker run, go to the Docker run reference.

   docker run -t -i -p 80:80 hello-world

   Note

   Output from the Apache web server is displayed in the terminal window. You can ignore the "Could not reliably determine the server's fully qualified domain name" message.

6. Open a browser and point to the server that is running Docker and hosting your container.

   • If you are using an EC2 instance, this is the Public DNS value for the server, which is the same address you use to connect to the instance with SSH. Make sure that the security group for your instance allows inbound traffic on port 80.

   • If you are running Docker locally, point your browser to http://localhost/.

   • If you are using docker-machine on a Windows or Mac computer, find the IP address of the VirtualBox VM that is hosting Docker with the docker-machine ip command, substituting machine-name with the name of the docker machine you are using.

     docker-machine ip machine-name

   You should see a web page with your "Hello World!" statement.

7. Stop the Docker container by typing Ctrl + c.

To tag your image and push it to Amazon ECR

1. Create an Amazon ECR repository to store your hello-world image. Note the repositoryUri in the output.

   aws ecr create-repository --repository-name hello-repository --region region

   Output:

   {
       "repository": {
           "registryId": "aws_account_id",
           "repositoryName": "hello-repository",
           "repositoryArn": "arn:aws:ecr:region:aws_account_id:repository/hello-repository",
           "createdAt": 1505337806.0,
           "repositoryUri": "aws_account_id.dkr.ecr.region.amazonaws.com/hello-repository"
       }
   }

2. Tag the hello-world image with the repositoryUri value from the previous step.

   docker tag hello-world aws_account_id.dkr.ecr.region.amazonaws.com/hello-repository

3. Run the aws ecr get-login-password command. Specify the registry URI you want to authenticate to. For more information, see Registry Authentication in the Amazon Elastic Container Registry User Guide.

   aws ecr get-login-password | docker login --username AWS --password-stdin aws_account_id.dkr.ecr.region.amazonaws.com

   Output:

   Login Succeeded

   Important

   If you receive an error, install or upgrade to the latest version of the AWS CLI. For more information, see Installing the AWS Command Line Interface in the AWS Command Line Interface User Guide.

4. Push the image to Amazon ECR with the repositoryUri value from the earlier step.

   docker push aws_account_id.dkr.ecr.region.amazonaws.com/hello-repository