2.2. Starting the Master Instance

Now we will start our master node, the instance that controls the rest of the nodes and the one with which users will interact directly.

Log in to the AWS Management Console if you have not already.
Click on EC2 Dashboard in the left-hand Navigation pane of the AWS Managment Console.
Click the Launch Instance button.
In the window that pops up:
1. Click the Community AMIs tab.
2. Enter the AMI ID (see Table 1.1, “WebMapReduce AMIs”) in the search box at the top.
3. Find that AMI in the list and click the Select button to the right.
In the next pane:
1. Optionally choose an instance type: Small (m1.small) instances are cheaper, but High-CPU Medium (c1.medium) instances offer significantly more computing power per dollar.
2. Click Continue.
In the next pane, leave all fields as their defaults. Click Continue.
In the next pane:
1. Select the "Create a new Key Pair" option if it is not already.
2. Choose an appropriate name for your key pair such as HadoopCluster_Keypair
3. Click Create and Download Key Pair. Remember where you save the downloaded keypair: you will need it to log in to your cluster.
4. Click Continue.
In the next pane:
1. Select the "Choose one or more of your existing Security Groups" option if it is not already.
2. Select both of the security groups you created earlier (Tip: to select multiple items in a list, hold down the Ctrl key on a PC or the Command key on a Mac while clicking the items).
3. Click Continue.
In the next pane, review your details and click Launch.

Your master instance will now start. Click Close, and click Instances in the left-hand Navigation pane. You should see your new instance listed (click Refresh in the top right toolbar if you do not see it). Once its status changes to "Running," select it. In the bottom pane, you should see information about your running instance. Three of these fields are of interest for this guide:

Public DNS: the domain name that you can use to communicate with your new instance from outside EC2, i.e., from your personal computer.
Private DNS: the domain name that other cluster nodes inside EC2 should use to communicate with your master instance.
Availability Zone: an identifier for the physical site where your instance is running. We will want to start slave instances at this same site.

Important

Pay attention to the difference between public and private DNS. We need to configure the slave nodes to communicate via the private DNS. If they use the public DNS, all communication between the nodes will incur extra network fees