INSTALL: Updates the IAM role section

Updates the instructions for the IAM instance role to use the instance
profile created by `eksctl` in hopes of making it less error prone.

INSTALL.md

@@ -166,81 +166,46 @@ Finally, note that if you want to launch in a specific availability zone, make s
 
 The instance we launch needs to be associated with an IAM role that allows for communication with EKS.
 
-If you also add SSM permissions, you can use Thar's default SSM agent to get a shell session on the instance.
+`eksctl` by default already creates such a role (and an instance profile that allows use of the role) as part of the cluster nodegroup.
 
-Here's how to create a role that allows both, and an instance profile that lets the instance use the role:
+The ARN of the IAM role can be retrieved with:
 
 ```
-aws iam create-role \
-   --role-name TharInstance \
-   --assume-role-policy-document '{ "Version": "2012-10-17", "Statement": [ { "Sid": "", "Effect": "Allow", "Principal": { "Service": "ec2.amazonaws.com" }, "Action": "sts:AssumeRole" } ] }'
-sleep 5
-aws iam attach-role-policy \
-   --role-name TharInstance \
-   --policy-arn arn:aws:iam::aws:policy/AmazonSSMManagedInstanceCore
-aws iam attach-role-policy \
-   --role-name TharInstance \
-   --policy-arn arn:aws:iam::aws:policy/AmazonEKSWorkerNodePolicy
-aws iam attach-role-policy \
-   --role-name TharInstance \
-   --policy-arn arn:aws:iam::aws:policy/AmazonEC2ContainerRegistryReadOnly
-aws iam attach-role-policy \
-   --role-name TharInstance \
-   --policy-arn arn:aws:iam::aws:policy/AmazonEKS_CNI_Policy
-aws iam create-instance-profile \
-   --instance-profile-name TharInstance
-aws iam add-role-to-instance-profile \
-   --instance-profile-name TharInstance \
-   --role-name TharInstance
+eksctl get iamidentitymapping --cluster thar
 ```
 
-Now we add the IAM role to the EKS cluster so it applies to new nodes.
-To do this, we edit the aws-auth ConfigMap using `kubectl`:
+The output should look like this:
 
 ```
-kubectl edit -n kube-system configmap/aws-auth
+ARN                                                               USERNAME                                GROUPS
+arn:aws:iam::YOUR_AWS_ACCOUNT_ID:role/INSTANCE_ROLE_NAME          system:node:{{EC2PrivateDNSName}}       system:bootstrappers,system:nodes
 ```
 
-Inside the file, we need to add the IAM role details to the `mapRoles` section.
-This is what the beginning of the file will look like, if your AWS account ID is 1234:
+Note down the INSTANCE_ROLE_NAME for the instructions below.
+
+If you add SSM permissions, you can use Thar's default SSM agent to get a shell session on the instance.
+
+To attach the role policy for SSM permissions, run the following:
 
 ```
- apiVersion: v1
- data:
-   mapRoles: |
-     - groups:
-       - system:bootstrappers
-       - system:nodes
-       rolearn: arn:aws:iam::1234:role/eksctl-thar-nodeg-NodeInstanceRole-IDENTIFIER
-       username: system:node:{{EC2PrivateDNSName}}
- kind: ConfigMap
+aws iam attach-role-policy \
+   --role-name INSTANCE_ROLE_NAME \
+   --policy-arn arn:aws:iam::aws:policy/AmazonSSMManagedInstanceCore
 ```
 
-We want to add the new role at the end of the `mapRoles` section, so it looks like this:
+Then, to retrieve the instance profile name used to launch instances, run this:
 
 ```
- apiVersion: v1
- data:
-   mapRoles: |
-     - groups:
-       - system:bootstrappers
-       - system:nodes
-       rolearn: arn:aws:iam::1234:role/eksctl-thar-nodeg-NodeInstanceRole-IDENTIFIER
-       username: system:node:{{EC2PrivateDNSName}}
-     - groups:
-       - system:nodes
-       rolearn: arn:aws:iam::1234:role/TharInstance
-       username: system:node:{{EC2PrivateDNSName}}
- kind: ConfigMap
+aws iam list-instance-profiles-for-role --role-name INSTANCE_ROLE_NAME --query "InstanceProfiles[*].InstanceProfileName" --output text
 ```
 
-Make sure you change "1234" to your AWS account ID: it's the same ID that appears a few lines up in the existing role.
-Save the file and confirm that the changes have been applied:
-
+There should only be one that looks like:
 ```
-kubectl describe configmap -n kube-system aws-auth
+eksctl-thar-nodegroup-ng-IDENTIFIER-NodeInstanceProfile-IDENTIFIER
 ```
 
+Note this down as the INSTANCE_PROFILE_NAME for the final launch command.
+
 ## Final launch details
 
 For the instance to be able to communicate with the EKS cluster control plane and other worker nodes, we need to make sure the instance is launched with the right security groups.
@@ -285,6 +250,7 @@ There are a few values to make sure you change in this command:
 * SECURITY_GROUP_ID_1, SECURITY_GROUP_ID_2: the two security groups you found earlier
 * THAR-AMI-ID: the ID of the AMI you registered, or an Amazon-provided AMI ID
 * userdata.toml: the path to the user data file you created earlier
+* INSTANCE_PROFILE_NAME: the instance profile created by `eksctl` for the cluster nodegroups. 
 
 ```
 aws ec2 run-instances --key-name YOUR_KEY_NAME \
@@ -295,7 +261,7 @@ aws ec2 run-instances --key-name YOUR_KEY_NAME \
    --region us-west-2 \
    --tag-specifications 'ResourceType=instance,Tags=[{Key=kubernetes.io/cluster/thar,Value=owned}]' \
    --user-data file://userdata.toml \
-   --iam-instance-profile Name=TharInstance
+   --iam-instance-profile Name=INSTANCE_PROFILE_NAME
 ```
 
 And remember, if you used a public subnet, add `--associate-public-ip-address` or attach an Elastic IP after launch.