MVP of templating

[mad01]

MVP implementation of templating to generate cluster.yaml file: related to #2404 implementation is using the text/template

cat > values.yaml <<EOF
clusterName: eu1
kubernetesVersion: 1.7.1
dnsZone: k8s.example.com
awsRegion: eu-west-1
EOF

cat > cluster.tmpl.yaml <<EOF
apiVersion: kops/v1alpha2
kind: InstanceGroup
metadata:
  labels:
	kops.k8s.io/cluster: {{.clusterName}}.{{.dnsZone}}
  name: nodes
spec:
  image: coreos.com/CoreOS-stable-1409.6.0-hvm
  machineType: m4.large
  maxPrice: "0.5"
  maxSize: 2
  minSize: 15
  role: Node
  rootVolumeSize: 100
  subnets:
  - {{.awsRegion}}a
  - {{.awsRegion}}b
  - {{.awsRegion}}c

EOF

running the templating command

  kops toolbox template \
      --values values.yaml \
      --template cluster.tmpl.yaml \
      --output cluster.yaml

output

apiVersion: kops/v1alpha2
kind: InstanceGroup
metadata:
  labels:
	kops.k8s.io/cluster: eu1.k8s.example.com
  name: nodes
spec:
  image: coreos.com/CoreOS-stable-1409.6.0-hvm
  machineType: m4.large
  maxPrice: "0.5"
  maxSize: 2
  minSize: 15
  role: Node
  rootVolumeSize: 100
  subnets:
  - eu-west-1a
  - eu-west-1b
  - eu-west-1c

[k8s-ci-robot]

Hi @mad01. Thanks for your PR.

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[chrislovecnm]

/ok-to-test

[mad01]

/assign @zmerlynn
I think this is good to go

[zmerlynn]

Hey, sorry, I thought I could get to this today but haven't had a chance.
/assign justinsb

[justinsb]

So I would have said that templating is probably out of scope, but the toolbox is where we do things that we think might be out of scope - it doesn't have the same guarantees that we'll continue to support it and doesn't have the same implication that things are core - although in practice things tend to wither rather than being removed :-)

I am wondering if we should force people to specify the style of templating they want to use. i.e. either pass a templatesyntax=go flag or specify the template using gotemplate. But I think we could add this later...

/lgtm

[k8s-github-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: justinsb, mad01

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[k8s-github-robot]

/test all [submit-queue is verifying that this PR is safe to merge]

[k8s-github-robot]

Automatic merge from submit-queue

[stefancocora]

I am wondering if we should force people to specify the style of templating they want to use. i.e. either pass a templatesyntax=go flag or specify the template using gotemplate. But I think we could add this later...

👍
This should be a feature imho.
Having users specify the style of templating makes things a lot clearer and more specific, removes ambiguity. Reduced ambiguity brings clarity and that is a very important point in my book !