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Getting Started, Part 4: Scaling Your App on a Cluster

Part 4: Scaling Your App on a Cluster

In Getting Started, Part 3: Stateful, Multi-container Applications, we figured out how to relate containers to each other. We organized an application into two simple services -- a frontend and a backend -- and defined how they are linked together.

In Part 4, we are going to take this application, which all ran on one host (a virtual or physical machine), and deploy it onto a cluster of hosts, just like we would in production.

Understanding Swarm clusters

Up until now you have been using Docker in a single-host mode on your local machine, which allows the client, which is the command-line interface (CLI), to make assumptions about how to operate. Namely, the client assumes that the Docker Daemon is running on the same host as the client. Single-host operations could also be done on remote machines with your client.

But Docker also can be switched into "swarm mode." A swarm is a group of hosts that are running Docker and have been joined into a cluster. After that has happened, you continue to run the Docker commands you're used to, but now the concept of a "host" changes from a single virtual or physical machine, to a swarm. And, "a single virtual or physical machine" is not referred to as a host, it's called a node -- or, a computing resource inside your cluster.

Before we get started: signup and configuration

The easiest way to demonstrate all this is to use Docker Cloud, which manages clusters that you run on popular cloud providers, like Heroku, Amazon Web Services (AWS), and so on. Because AWS has a free tier of service, which lets you provision low-resource virtual machines for free, we're going to use that to learn these concepts. We're also not going to be using any of Docker Cloud's paid features, so let's dive in and deploy something!

Sign up for AWS, and configure it

All we have to do to let Docker Cloud manage nodes for us on free-tier AWS is create a service policy that grants certain permissions, and apply that to an identity called a "role," using AWS's Identity and Access Management (IAM) tool.

  • Go to [http://aws.amazon.com] and sign up for an account. It's free.

  • Go to the IAM panel

  • Click Create Policy, then Create Your Own Policy.

  • Name the policy dockercloud-policy and paste the following text in the space provided for Policy Document, then click Create Policy.

    {
  "Version": "2012-10-17",
  "Statement": [
    {
      "Action": [
        "ec2:*",
        "iam:ListInstanceProfiles"
      ],
      "Effect": "Allow",
      "Resource": "*"
    }
  ]
}

  • Now create a role with a name of your choice.

  • Select Role for Cross-Account Access, and in the submenu that opens select Allows IAM users from a 3rd party AWS account to access this account.

  • In the Account ID field, enter the ID for the Docker Cloud service: 689684103426.

  • In the External ID field, enter your Docker Cloud username.

  • On the next screen, select the dockercloud-policy you created to attach to the role.

  • On next page review your entries and copy the full Role ARN string. The ARN string should look something like arn:aws:iam::123456789123:role/dockercloud-role. You'll use the ARN in the next step.

  • Finally, click Create Role.

And you've done it! Your AWS account will allow Docker Cloud to control virtual machines, if we configure Docker Cloud to use the role you've created. So, let's do that now.

Note: If you had any trouble along the way, there are more detailed instructions in the Docker Cloud docs. If you'd like to use a cloud provider besides AWS, check out the list. We're just using AWS here because you don't have to pay.

Configure Docker Cloud to manage to your AWS instances

  • Go to http://cloud.docker.com and sign in with the same Docker ID you used in step 2.
  • Click Settings, and in the Cloud Providers section, click the plug icon.
  • Enter the Role ARN string you copied earlier, e.g. arn:aws:iam::123456789123:role/dockercloud-role.
  • Click Save.

And now, Docker Cloud can create and manage instances for you, and turn them into a swarm.

Creating your first Swarm cluster

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