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‎getting-started/part4.md‎

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---
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title: "Getting Started, Part 4: Scaling Your App on a Cluster"
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---
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In [Getting Started, Part 3: Stateful, Multi-container Applications](part3.md),
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we figured out how to relate containers to each other. We organized an
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application into two simple services -- a frontend and a backend -- and defined
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how they are linked together.
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In Part 4, we are going to take this application, which all ran on one **host**
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(a virtual or physical machine), and deploy it onto a cluster of hosts, just
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like we would in production.
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## Understanding Swarm clusters
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Up until now you have been using Docker in a single-host mode on your local
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machine, which allows the client, which is the command-line interface (CLI), to
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make assumptions about how to operate. Namely, the client assumes that the
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Docker Daemon is running on the same host as the client. Single-host operations
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could also be done on remote machines with your client.
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But Docker also can be switched into "swarm mode." A swarm is a group of hosts
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that are running Docker and have been joined into a cluster. After that has
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happened, you continue to run the Docker commands you're used to, but now the
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concept of a "host" changes from a single virtual or physical machine, to a
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swarm. And, "a single virtual or physical machine" is not referred to as a host,
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it's called a node -- or, a computing resource inside your cluster.
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## Before we get started: signup and configuration
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The easiest way to demonstrate all this is to use Docker Cloud, which manages
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clusters that you run on popular cloud providers, like Heroku, Amazon Web
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Services (AWS), and so on. Because AWS has a free tier of service, which lets
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you provision low-resource virtual machines for free, we're going to use that
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to learn these concepts. We're also not going to be using any of Docker Cloud's
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paid features, so let's dive in and deploy something!
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### Sign up for AWS, and configure it
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All we have to do to let Docker Cloud manage nodes for us on free-tier AWS is
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create a service policy that grants certain permissions, and apply that to an
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identity called a "role," using AWS's Identity and Access Management (IAM) tool.
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- Go to [aws.amazon.com](https://aws.amazon.com) and sign up for an account. It's free.
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- Go to [the IAM panel](https://console.aws.amazon.com/iam/home#policies)
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- Click **Create Policy**, then **Create Your Own Policy**.
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- Name the policy `dockercloud-policy` and paste the following text in the
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space provided for **Policy Document**, then click **Create Policy**.
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```json
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{
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"Version": "2012-10-17",
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"Statement": [
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{
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"Action": [
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"ec2:*",
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"iam:ListInstanceProfiles"
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],
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"Effect": "Allow",
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"Resource": "*"
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}
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]
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}
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```
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- Now [create a role](https://console.aws.amazon.com/iam/home#roles) with a name
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of your choice.
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- 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**.
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- In the **Account ID** field, enter the ID for the Docker Cloud service: `689684103426`.
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- In the **External ID** field, enter your Docker Cloud username.
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- On the next screen, select the `dockercloud-policy` you created to attach to the role.
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- On next page review your entries and copy the full **Role ARN** string. The
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ARN string should look something like `arn:aws:iam::123456789123:role/dockercloud-role`. You'll use the ARN in the next step.
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- Finally, click **Create Role**.
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And you've done it! Your AWS account will allow Docker Cloud to control
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virtual machines, if we configure Docker Cloud to use the role you've created.
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So, let's do that now.
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> Note: If you had any trouble along the way, there are more detailed
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[instructions in the Docker Cloud docs](/docker-cloud/infrastructure/link-aws.md).
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If you'd like to use a cloud provider besides AWS, check out
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[the list](/docker-cloud/infrastructure/index.md). We're just using AWS here
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because you don't have to pay.
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### Configure Docker Cloud to manage to your AWS instances
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- Go to [cloud.docker.com](http://cloud.docker.com) and sign in with the
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same Docker ID you used in [part 2](/getting-started/part2.md).
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- Click **Settings**, and in the Cloud Providers section, click the plug icon.
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- Enter the Role ARN string you copied earlier, e.g. `arn:aws:iam::123456789123:role/dockercloud-role`.
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- Click **Save**.
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And now, Docker Cloud can create and manage instances for you, and turn them
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into a swarm.
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## Creating your first Swarm cluster
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1. Go back to Docker Cloud by visiting [cloud.docker.com](https://cloud.docker.com).
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2. Click **Node Clusters** in the left navigation, then click the **Create** button.
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This pulls up a form where you can create our cluster.
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3. Leave everything default, except:
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- Name: Give your cluster a name
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- Region: Select a region that's close to you
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- Provider: Set to "Amazon Web Services"
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- Type/Size: Select the `t2.nano` option as that is free-tier
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4. Launch the cluster by clicking **Launch node cluster**; this will spin
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up a free-tier Amazon instance.
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5. Now, click **Services** in the left navigation, then the **Create** button,
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then the **globe icon**.
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6. Search Docker Hub for the image you uploaded
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[On to next >>](part5.md){: class="button darkblue-btn"}

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