Update default reserved memory calculation to match new calculation u…

…sed in amazon-eks-ami

The reserved memory calculation was recently changed in amazon-eks-ami to be
based on pod density (11*maxPodsPerNode+255) instead of total memory.
See https://github.com/awslabs/amazon-eks-ami/blob/21426e27e3845319dbca92e7df32e5c4b984a1d1/files/bootstrap.sh#L163

This commit introduces a new property on InstanceTypeInfo to store MaxPodsPerNode
and populates it using the already available data that has been generated into
maxpods.go.

Because the image type specs (cpu, memory) come from an API call the the max
number of pods per node comes from a file in amaxon-eks-ami, there is a chance
that an image type is returned by the API for which there is no corresponding
record in maxpods.go. To handle this, I left the original memory calculation
in place as a fallback that will be used if max pods per node cannot be
determined.

Issue eksctl-io#2395

pkg/cfn/builder/api_test.go

@@ -344,7 +344,7 @@ func completeKubeletConfig(kubeletConfigAssetContent []byte, clusterDNS string)
 		"kubeReserved:\n" +
 		"  cpu: 70m\n" +
 		"  ephemeral-storage: 1Gi\n" +
-		"  memory: 1843Mi\n"
+		"  memory: 574Mi\n"
 }
 
 var _ = Describe("CloudFormation template builder API", func() {

pkg/nodebootstrap/reserved.go

@@ -62,6 +62,8 @@ type InstanceTypeInfo struct {
 	Memory int64
 	// CPU count.
 	CPU int64
+	// Max pods per node
+	MaxPodsPerNode int64
 }
 
 // NewInstanceTypeInfo creates a simple version of ec2.InstanceTypeInfo
@@ -80,6 +82,9 @@ func NewInstanceTypeInfo(ec2info *ec2.InstanceTypeInfo) InstanceTypeInfo {
 	if ec2info.VCpuInfo != nil {
 		i.CPU = aws.Int64Value(ec2info.VCpuInfo.DefaultVCpus)
 	}
+	if maxPodsPerNode, exists := maxPodsPerNodeType[*ec2info.InstanceType]; exists {
+		i.MaxPodsPerNode = int64(maxPodsPerNode)
+	}
 	return i
 }
 
@@ -93,17 +98,17 @@ func (i InstanceTypeInfo) DefaultStorageToReserve() string {
 
 // DefaultMemoryToReserve returns how much memory to reserve.
 //
-// See https://github.com/awslabs/amazon-eks-ami/blob/ff690788dfaf399e6919eebb59371ee923617df4/files/bootstrap.sh#L150-L181
-// which takes it form https://cloud.google.com/kubernetes-engine/docs/concepts/cluster-architecture#node_allocatable
-//
-// 255 Mi of memory for machines with less than 1024Mi of memory
-// 25% of the first 4096Mi of memory
-// 20% of the next 4096Mi of memory (up to 8192Mi)
-// 10% of the next 8192Mi of memory (up to 16384Mi)
-// 6% of the next 114688Mi of memory (up to 131072Mi)
-// 2% of any memory above 131072Mi
+// See https://github.com/awslabs/amazon-eks-ami/blob/21426e27e3845319dbca92e7df32e5c4b984a1d1/files/bootstrap.sh#L154-L165
 func (i InstanceTypeInfo) DefaultMemoryToReserve() string {
-	mib := memProgression.calculate(i.Memory, minimumMemoryToReserve)
+	var mib int64
+	if i.MaxPodsPerNode > 0 {
+		mib = 11*i.MaxPodsPerNode + minimumMemoryToReserve
+	} else {
+		// As a fallback, if MaxPodsPerNode is 0, use the original calculation, which is a progressive calculation based on total memory.
+		// See https://github.com/awslabs/amazon-eks-ami/blob/ff690788dfaf399e6919eebb59371ee923617df4/files/bootstrap.sh#L150-L181
+		// which takes it from https://cloud.google.com/kubernetes-engine/docs/concepts/cluster-architecture#node_allocatable
+		mib = memProgression.calculate(i.Memory, minimumMemoryToReserve)
+	}
 	return fmt.Sprintf("%dMi", mib)
 }