mirror of https://github.com/kubernetes/kops.git
100 lines
4.3 KiB
Markdown
100 lines
4.3 KiB
Markdown
# Cluster Templating
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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)).
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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)).
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This document details the template language used.
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The file passed as `--template` must be a [go template](https://golang.org/pkg/text/template/). Example:
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```yaml
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# File cluster.tmpl.yaml
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apiVersion: kops/v1alpha2
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kind: InstanceGroup
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metadata:
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labels:
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kops.k8s.io/cluster: {{.clusterName}}.{{.dnsZone}}
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name: nodes
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spec:
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image: coreos.com/CoreOS-stable-1409.6.0-hvm
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kubernetesVersion: {{.kubernetesVersion}
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machineType: m4.large
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maxPrice: "0.5"
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maxSize: 2
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minSize: 15
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role: Node
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rootVolumeSize: 100
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subnets:
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- {{.awsRegion}}a
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- {{.awsRegion}}b
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- {{.awsRegion}}c
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```
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You can pass configuration such as an environment file by using the `--values PATH` command line option. Note `--values` is a slice so can be defined multiple times; the configuration is overridden by each configuration file *(so order is important assuming duplicating values)*; a use-case for this would be a default configuration which upstream clusters can override.
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The file passed as `--values` must contain the variables referenced in the template. Example:
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```yaml
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# File values.yaml
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clusterName: eu1
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kubernetesVersion: 1.7.1
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dnsZone: k8s.example.com
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awsRegion: eu-west-1
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```
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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`.
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Note: when creating a cluster desired configuration template, you can
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- 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 [cluster_spec.md](cluster_spec.md).
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- replace values by placeholders in that file to create the template.
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### Templates
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The `--template` command line option can point to either a specific file or a directory with a collection of templates. An example usage would be;
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```shell
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$ kops toolbox template --values dev.yaml --template cluster.yaml --template instance_group_directory
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```
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The cluster.yaml *(your main cluster spec for example)* would be written first followed by any templates found in the instance_group_directory directory. Note the toolbox will automatically add YAML separators between the documents for you.
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### Snippets
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The toolbox template also supports the reuse or break up of code blocks into snippets directories. By passing a `--snippets PATH` to a directory holding templates;
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```shell
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$ kops toolbox template --values dev.yaml --template cluster.yaml --template instancegroups --snippets snippets
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```
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The example below assumes you have placed the appropriate files i.e. *(nodes.json, master.json etc)* in to the snippets directory. Note, the namespace of the snippets are flat and always the basename() of the file path; so `snippets/components/docker.options` is still referred to as 'docker.options'.
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```YAML
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apiVersion: kops/v1alpha2
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kind: Cluster
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metadata:
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name: {{ .environment }}.{{ .dns_zone }}
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spec:
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docker:
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{{ include "docker" . | indent 4 }}
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additionalPolicies:
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master: |
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{{ include "masters.json" . | indent 6 }}
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node: |
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{{ include "nodes.json" . | indent 6 }}
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```
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### Template Functions
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The entire set of https://github.com/Masterminds/sprig functions are available within the templates for you. Note if you want to use the 'defaults' functions switch off the verification check on the command line by `--fail-on-missing=false`;
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```YAML
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image: {{ default $image $node.image }}
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machineType: {{ default $instance $node.machine_type }}
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maxSize: {{ default "10" $node.max_size }}
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minSize: {{ default "1" $node.min_size }}
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```
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### Formatting
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Formatting in golang templates is a pain! At the start or at the end of a statement can be infuriating to get right, so a `--format-yaml=true` *(defaults to false)* command line option has been added. This will first unmarshal the generated content *(performing a syntax verification)* and then marshal back the content removing all those nasty formatting issues, newlines etc.
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