kops/docs/cluster_template.md

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# Cluster template
The command `kops replace` can replace a cluster desired configuration from the config in a yaml file (see [/cli/kops_replace.md](/cli/kops_replace.md)).
It is possible to generate that yaml file from a template, using the command `kops toolbox template` (see [cli/kops_toolbox_template.md](cli/kops_toolbox_template.md)).
This document details the template language used.
The file passed as `--template` must be a [go template](https://golang.org/pkg/text/template/). Example:
```yaml
# File cluster.tmpl.yaml
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
kubernetesVersion: {{.kubernetesVersion}
machineType: m4.large
maxPrice: "0.5"
maxSize: 2
minSize: 15
role: Node
rootVolumeSize: 100
subnets:
- {{.awsRegion}}a
- {{.awsRegion}}b
- {{.awsRegion}}c
```
The file passed as `--values` must contain the variables referenced in the template. Example:
```yaml
# File values.yaml
clusterName: eu1
kubernetesVersion: 1.7.1
dnsZone: k8s.example.com
awsRegion: eu-west-1
```
Running `kops toolbox template` replaces the placeholders in the template by values and generates the file output.yaml, which can then be used to replace the desired cluster configuration with `kops replace -f cluster.yaml`.
Note:
When creating a cluster desired configuration template, you can
- use `kops get k8s-cluster.example.com -o yaml > cluster-desired-config.yaml` to create the cluster desired configuration file (see [cli/kops_get.md](cli/kops_get.md)). The values in this file are defined in [cli/cluster_spec.md](cli/cluster_spec.md).
- replace values by placeholders in that file to create the template.