Convert InstanceType to a CSV

This is super ugly internally, but it presents a possibly OK interface
to users of the stack.

Users can specify 1-4 instance types separated by commas. When
launching OnDemand instances, the types will be attempted in priority
order. When launching spot instances (if they're enabled) all types are
considered.

Internally, this is implemented by appending 3 commas to the
InstanceType and re-splitting it (to ensure there's ALWAYS at least 4
list items passed to !Select.

Author: yob

templates/aws-stack.yml

@@ -39,9 +39,6 @@ Metadata:
         - ImageId
         - ImageIdParameter
         - InstanceType
-        - InstanceType2
-        - InstanceType3
-        - InstanceType4
         - AgentsPerInstance
         - KeyName
         - SecretsBucket
@@ -207,7 +204,7 @@ Parameters:
     Default: ""
 
   InstanceType:
-    Description: Instance type
+    Description: Instance type. Comma separated list with 1-4 instance types. The order is a prioritised preference for launching OnDemand instances, and an non-prioritised list of types to consider for Spot Instances (where used).
     Type: String
     Default: t3.large
     MinLength: 1
@@ -223,21 +220,6 @@ Parameters:
     Type: Number
     Default: 0
 
-  InstanceType2:
-    Description: The secondary instance type to use when requesting mixed instances. Omit this parmameter to only request 1 instance type.
-    Type: String
-    Default: ""
-
-  InstanceType3:
-    Description: The tertiary instance type to use when requesting mixed instances. Omit this parmameter to only request 2 instance types.
-    Type: String
-    Default: ""
-
-  InstanceType4:
-    Description: The quaternary instance type to use when requesting mixed instances. Omit this parmameter to only request 3 instance types.
-    Type: String
-    Default: ""
-
   OnDemandPercentage:
     Description: Percentage of total instances that should launch as OnDemand. Reduce this to use some Spot Instances when they're available.
     Type: Number
@@ -465,13 +447,13 @@ Conditions:
       !Equals [ !Ref RootVolumeName, "" ]
 
     UseInstanceType2:
-      !Not [ !Equals [ !Ref InstanceType2, ""] ]
+      !Not [ !Equals [ !Select [ "1", !Split [ ",", !Join [ ",", [ !Ref InstanceType, "", "", "" ] ] ] ], ""] ]
 
     UseInstanceType3:
-      !Not [ !Equals [ !Ref InstanceType3, ""] ]
+      !Not [ !Equals [ !Select [ "2", !Split [ ",", !Join [ ",", [ !Ref InstanceType, "", "", "" ] ] ] ], ""] ]
 
     UseInstanceType4:
-      !Not [ !Equals [ !Ref InstanceType4, ""] ]
+      !Not [ !Equals [ !Select [ "3", !Split [ ",", !Join [ ",", [ !Ref InstanceType, "", "", "" ] ] ] ], ""] ]
 
     UseManagedPolicyARN:
       !Not [ !Equals [ !Join [ "", !Ref ManagedPolicyARN ], "" ] ]
@@ -830,7 +812,7 @@ Resources:
           KeyName: !If [ "HasKeyName", !Ref KeyName, !Ref 'AWS::NoValue' ]
           IamInstanceProfile:
             Arn: !GetAtt "IAMInstanceProfile.Arn"
-          InstanceType: !Ref InstanceType
+          InstanceType: !Select [ "0", !Split [ ",", !Join [ ",", [ !Ref InstanceType, "", "", "" ] ] ] ]
           ImageId: !If [ HasImageId, !Ref ImageId, !If [ HasImageIdParameter, !GetAtt ImageIdParameterStack.Outputs.ImageId, !FindInMap [ AWSRegion2AMI, !Ref 'AWS::Region', !Ref InstanceOperatingSystem ] ] ]
           BlockDeviceMappings:
             - DeviceName: !If [ UseDefaultRootVolumeName, !If [ UseWindowsAgents, /dev/sda1, /dev/xvda ], !Ref RootVolumeName ]
@@ -944,18 +926,18 @@ Resources:
             LaunchTemplateId: !Ref AgentLaunchTemplate
             Version: !GetAtt "AgentLaunchTemplate.LatestVersionNumber"
           Overrides:
-          - InstanceType: !Ref InstanceType
+          - InstanceType: !Select [ "0", !Split [ ",", !Join [ ",", [ !Ref InstanceType, "", "", "" ] ] ] ]
           - InstanceType: !If
             - UseInstanceType2
-            - !Ref InstanceType2
+            - !Select [ "1", !Split [ ",", !Join [ ",", [ !Ref InstanceType, "", "", "" ] ] ] ]
             - !Ref "AWS::NoValue"
           - InstanceType: !If
             - UseInstanceType3
-            - !Ref InstanceType3
+            - !Select [ "2", !Split [ ",", !Join [ ",", [ !Ref InstanceType, "", "", "" ] ] ] ]
             - !Ref "AWS::NoValue"
           - InstanceType: !If
             - UseInstanceType4
-            - !Ref InstanceType4
+            - !Select [ "3", !Split [ ",", !Join [ ",", [ !Ref InstanceType, "", "", "" ] ] ] ]
             - !Ref "AWS::NoValue"
       MinSize: !Ref MinSize
       MaxSize: !Ref MaxSize