AWS: Change master to m3.medium by default

m3.large for > 150 nodes.

t2.micro often runs out of memory.  The t2 class has very
difficult-to-understand behaviour when it runs out of CPU.  The
m3.medium is reasonably affordable, and avoids these problems.

Fix #21151

Issue #18975

cluster/aws/config-default.sh

@@ -33,12 +33,10 @@ fi
 # Dynamically set the master size by the number of nodes, these are guesses
 # TODO: gather some data
 if [[ -z ${MASTER_SIZE} ]]; then
-  if (( ${NUM_NODES} < 50 )); then
+  if (( ${NUM_NODES} < 150 )); then
-    MASTER_SIZE="t2.micro"
+    MASTER_SIZE="m3.medium"
-  elif (( ${NUM_NODES} < 150 )); then
-    MASTER_SIZE="t2.small"
   else
-    MASTER_SIZE="t2.medium"
+    MASTER_SIZE="m3.large"
   fi
 fi
 

cluster/aws/config-test.sh

@@ -34,12 +34,10 @@ fi
 # Dynamically set the master size by the number of nodes, these are guesses
 # TODO: gather some data
 if [[ -z ${MASTER_SIZE} ]]; then
-  if (( ${NUM_NODES} < 50 )); then
+  if (( ${NUM_NODES} < 150 )); then
-    MASTER_SIZE="t2.micro"
+    MASTER_SIZE="m3.medium"
-  elif (( ${NUM_NODES} < 150 )); then
-    MASTER_SIZE="t2.small"
   else
-    MASTER_SIZE="t2.medium"
+    MASTER_SIZE="m3.large"
   fi
 fi
 

docs/getting-started-guides/aws.md

@@ -85,6 +85,7 @@ You can override the variables defined in [config-default.sh](http://releases.k8
 ```bash
 export KUBE_AWS_ZONE=eu-west-1c
 export NUM_NODES=2
+export MASTER_SIZE=m3.medium
 export NODE_SIZE=m3.medium
 export AWS_S3_REGION=eu-west-1
 export AWS_S3_BUCKET=mycompany-kubernetes-artifacts
@@ -92,14 +93,44 @@ export INSTANCE_PREFIX=k8s
 ...
 ```
 
-If you don't specify master and minion sizes, the scripts will attempt to guess the correct size of the master and worker nodes based on `${NUM_NODES}`. In
+If you don't specify master and minion sizes, the scripts will attempt to guess
-particular, for clusters less than 50 nodes it will use a `t2.micro`, for clusters between 50 and 150 nodes it will use a `t2.small` and for clusters with
+the correct size of the master and worker nodes based on `${NUM_NODES}`. In
-greater than 150 nodes it will use a `t2.medium`.
+version 1.2 these default are:
+
+* For the master, for clusters of less than 150 nodes it will use an
+  `m3.medium`, for clusters of greater than 150 nodes it will use an
+  `m3.large`.
+
+* For worker nodes, for clusters less than 50 nodes it will use a `t2.micro`,
+  for clusters between 50 and 150 nodes it will use a `t2.small` and for
+  clusters with greater than 150 nodes it will use a `t2.medium`.
 
 WARNING: beware that `t2` instances receive a limited number of CPU credits per hour and might not be suitable for clusters where the CPU is used
 consistently. As a rough estimation, consider 15 pods/node the absolute limit a `t2.large` instance can handle before it starts exhausting its CPU credits
 steadily, although this number depends heavily on the usage.
 
+In prior versions of kubernetes, we defaulted the master node to a t2-class
+instance, but found that this sometimes gave hard-to-diagnose problems when the
+master ran out of memory or CPU credits.  If you are running a test cluster
+and want to save money, you can specify `export MASTER_SIZE=t2.micro` but if
+your master pauses do check the CPU credits in the AWS console.
+
+For production usage, we recommend at least `export MASTER_SIZE=m3.medium` and
+`export NODE_SIZE=m3.medium`.  And once you get above a handful of nodes, be
+aware that one m3.large instance has more storage than two m3.medium instances,
+for the same price.
+
+We generally recommend the m3 instances over the m4 instances, because the m3
+instances include local instance storage.  Historically local instance storage
+has been more reliable than AWS EBS, and performance should be more consistent.
+The ephemeral nature of this storage is a match for ephemeral container
+workloads also!
+
+If you use an m4 instance, or another instance type which does not have local
+instance storage, you may want to increase the `NODE_ROOT_DISK_SIZE` value,
+although the default value of 32 is probably sufficient for the smaller
+instance types in the m4 family.
+
 The script will also try to create or reuse a keypair called "kubernetes", and IAM profiles called "kubernetes-master" and "kubernetes-minion".
 If these already exist, make sure you want them to be used here.