Add kops toolbox template docs

docs/README.md

@@ -45,6 +45,7 @@
 * [Cluster addon manager](addon_manager.md)
 * [Cluster addons](addons.md)
 * [Cluster configuration management](changing_configuration.md)
+* [Cluster desired configuration creation from template](cluster_template.md)
 * [Cluster upgrades and migrations](cluster_upgrades_and_migrations.md)
 * [`etcd` volume encryption setup](etcd_volume_encryption.md)
 * [`etcd` backup setup](etcd_backup.md)

docs/cluster_template.md

@@ -0,0 +1,48 @@
+# 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.