Update custom SSH configuration, add instructions

Update custom SSH configuration to use directory-specific known hosts file. Add preliminary set of instructions. Not quite ready to merge yet; CentOS Atomic Host on AWS seems to have an issue starting the Docker service.

Signed-off-by: Scott Lowe <scott.lowe@scottlowe.org>

centos-atomic/docker-cloudinit/README.md

@@ -0,0 +1,38 @@
+# Instructions
+
+1. Capture the VPC ID of your default VPC using this command:
+
+        VPC_ID=$(aws --output text ec2 describe-vpcs \
+        --filters Name=isDefault,Values="true" \
+        --query 'Vpcs[0].VpcId')
+
+2. Capture the subnet ID of one of the subnets (the first, by default) in the default VPC using this command (step 1 must be completed first):
+
+        SN_ID=$(aws --output text ec2 describe-subnets \
+        --filters Name=vpc-id,Values="$VPC_ID" \
+        --query 'sort_by(Images,&AvailabilityZone)[0].SubnetId')
+
+3. Capture the security group ID of a security group in the default VPC with the name "default" (it is assumed that this security group exists and allows SSH access to the instance; if this is not the case, you must fix this outside of this process):
+
+        SG_ID=$(aws --output text ec2 describe-security-groups \
+        --filters Name=group-name,Values="default" \
+        Name=vpc-id,Values="$VPC_ID" \
+        --query 'SecurityGroups[0].GroupId')
+
+4. Finally, capture the image ID of the latest version of the CentOS 7 Atomic Host AMI using this command:
+
+        IMAGE_ID=$(aws --output text ec2 describe-images \
+        --owners 410186602215 --filter Name=name,Values="*CentOS Atomic*" \
+        --query 'sort_by(Images,&CreationDate)[-1].ImageId')
+
+5. Make sure you have an SSH key available to use with the instance and make note of the name of the SSH key.
+
+6. Launch an AWS instance using this command:
+
+        aws ec2 run-instances --image-id $IMAGE_ID --instance-type t2.micro \
+        --key-name keyname --user-data file://cloud-config.yml \
+        --subnet-id $SN_ID --security-group-ids $SG_ID
+
+7. Connect to the instance using SSH.
+
+8. Verify that the Docker daemon is listening over a network socket (not the default configuration) by running `ss -lnt` and/or running `docker` commands against the network socket (via `-H tcp://127.0.0.1:2375`).

centos-atomic/docker-cloudinit/ssh.cfg

@@ -1,2 +1,4 @@
+UserKnownHostsFile ./known_hosts
+
 Host *
   PubkeyAuthentication yes