Kubernetes templates made easy.
#keep-it-simple #no-server-component

Features:

• Template flavor of your choice
  • $ ($VAR / ${VAR});
  • go-template (go-template enriched with sprig);
  • template-kind (kind: Template).
• Support for *.env (<VAR>=<VAL>) and YAML / JSON config files.
• Fail-fast defaults (all variables must be given a value (unless explicitly marked optional)).
• ConfigMap/Secret freezing for easier and less error-prone ConfigMap/Secret rollouts
  (something to consider if when you hit kubernetes/kubernetes#22368).
• ConfigMap/Secret "data-from-file" injection when kubectl create configmap ... --from-file=... --from-file=... --from-file=... ... feels like too much typing.
• image:tag -> image@digest pinning with the help of dockry
  (e.g. kubetpl render -s IMAGE=$(dockry digest --fq user/image:master) ... to force redeployment of the new build published under the same tag).

curl -sSL https://github.com/shyiko/kubetpl/releases/download/0.9.0/kubetpl-0.9.0-$(
    bash -c '[[ $OSTYPE == darwin* ]] && echo darwin || echo linux'
  )-amd64 -o kubetpl && chmod a+x kubetpl && sudo mv kubetpl /usr/local/bin/

Verify PGP signature (optional but recommended):

curl -sSL https://github.com/shyiko/kubetpl/releases/download/0.9.0/kubetpl-0.9.0-$(
    bash -c '[[ $OSTYPE == darwin* ]] && echo darwin || echo linux'
  )-amd64.asc -o kubetpl.asc
curl -sS https://keybase.io/shyiko/pgp_keys.asc | gpg --import
gpg --verify kubetpl.asc /usr/local/bin/kubetpl

macOS: gpg can be installed with brew install gnupg

Download executable from the Releases page.

# create template
echo $'
# kubetpl:syntax:$

apiVersion: v1
kind: Pod
metadata:
  name: $NAME-pod
spec:
  containers:
  - name: $NAME-container
    image: $IMAGE
    env:
    - name: ENV_KEY
      value: $ENV_KEY
' > template.yml 

# create config file (.env, .yml/.yaml or .json) (optional)
# (you'll probably have a different config file for each cluster/namespace/etc)
echo $'
NAME=sample-app
ENV_KEY=value
' > staging.env
# you might not need a config file if there are only a handful of variables (like in this case)
# -s/--set key=value might be enough

# render template
kubetpl render template.yml -i staging.env -s IMAGE=nginx 

# to apply, pipe "render"ed output through kubectl    
kubetpl render template.yml -i staging.env -s IMAGE=nginx | 
  kubectl apply -f -
  
# you can also apply remote template(s) 
kubetpl render https://rawgit.com/shyiko/kubetpl/master/example/nginx.sh.yml \
  -s NAME=kubetpl-example-nginx -s MESSAGE="hello $(whoami)" | 
  kubectl apply -f -

(for more examples see Template flavors)

# bash
source <(kubetpl completion bash)

# zsh
source <(kubetpl completion zsh)

When kubetpl render --freeze ... is used, kubetpl rewrites ConfigMap/Secret's name to include hash of the content and then updates all the references (in Pods / DaemonSets / Deployments / Jobs / ReplicaSets / ReplicationControllers / StatefulSets / CronJobs) with a new value.

For example, executing kubetpl render --freeze example/nginx-with-data-from-file.yml -s NAME=app -s MESSAGE=msg should produce example/nginx-with-data-from-file.rendered+frozen.yml.

NOTE: this feature can be used regardless of the Template flavor choice (or lack thereof (i.e. on its own)).

kubetpl@0.5.0+ also supports kubetpl/data-from-env-file.

Optionally, ConfigMap/Secret|s can be extended with kubetpl/data-from-file to load "data" from a list of files (relative to a template unless a different -c/--chroot is specified), e.g.

kind: ConfigMap
kubetpl/data-from-file: 
  - file 
  - path/to/another-file
  - custom-key=yet-another-file
data:
  key: value
...

Upon kubetpl render the content of file, another-file and yet-another-file (using custom-key as a key) will be added to the object's "data" (kubetpl/data-from-file is automatically striped away).

For example, executing kubetpl render --allow-fs-access example/nginx-with-data-from-file.yml -s NAME=app should produce example/nginx-with-data-from-file.rendered.yml.

NOTE #1: for security reasons, kubetpl/data-form-file is not allowed to read files unless --allow-fs-access or -c/--chroot=<root dir> is specified (see kubetpl render --help for more).

NOTE #2: this feature can be used regardless of the Template flavor choice (or lack thereof (i.e. on its own)).

Template syntax is determined by first checking template for # kubetpl:syntax:<$|go-template|template-kind> comment and then, if not found, --syntax=<$|go-template|template-kind> command line option. In the absence of both, kubetpl assumes that template is a regular resource definition file.

A type of template where all instances of $VAR / ${VAR} are replaced with corresponding values. If, for some variable, no value is given - an error will be raised.

Use $$ when you need a literal dollar sign ($$v is interpreted as $v string and not '$' + <value_of_v>).

Let's say we have the following (click to expand):

NAME=sample-app
REPLICAS=1

# kubetpl:syntax:$

apiVersion: v1
kind: Service
metadata:
  name: $NAME-service
spec:
  selector:
    app: $NAME
  ports:
  - protocol: TCP
    port: 80
---
apiVersion: apps/v1beta1
kind: Deployment
metadata:
  name: $NAME-deployment
spec:
  replicas: $REPLICAS
  template: 
    metadata:
      labels:
        app: $NAME
    spec:
      containers:
      - name: nginx
        image: nginx:1.7.9
        ports:
        - containerPort: 80

kubetpl render k8s/template.yml -i k8s/staging.env -s REPLICAS=3 should then yield

apiVersion: v1
kind: Service
metadata:
  name: sample-app-service
spec:
  selector:
    app: sample-app
  ports:
  - protocol: TCP
    port: 80
---
apiVersion: apps/v1beta1
kind: Deployment
metadata:
  name: sample-app-deployment
spec:
  replicas: 3
  template: 
    metadata:
      labels:
        app: sample-app
    spec:
      containers:
      - name: nginx
        image: nginx:1.7.9
        ports:
        - containerPort: 80

kubetpl@0.8.0+ default values can be specified via # kubetpl:set:KEY=VALUE directive(s), e.g.

# kubetpl:syntax:$
# kubetpl:set:NAME=nginx
# kubetpl:set:REPLICAS=1

apiVersion: apps/v1beta1
kind: Deployment
metadata:
  name: $NAME
  annotations:
    version: $VERSION
spec:
  replicas: $REPLICAS
...  

All functions provided by sprig are available
(with the exception of env and expandenv).

A good overview of go-template|s can be found here. You might also want to check official documentation.

Some of the most commonly used expressions:

• {{ .VAR }} - get the value of VAR;
• {{ if isset "VAR" }} ... {{ end }} - render content between }} and {{ only if .VAR is set;
• {{ get "VAR" "default" }} - get the value of VAR, return "default" if not set (e.g. {{ get "REPLICAS" 1 }});
• {{ .VAR | quote }} - quote the value of VAR;
• {{ .VAR | indent 4 }} - indent value of VAR with 4 spaces;
• {{ .VAR | b64enc }} - base64-encode value of VAR.

Let's say we have the following (click to expand):

NAME=sample-app
REPLICAS=1

# kubetpl:syntax:go-template

apiVersion: v1
kind: Service
metadata:
  name: {{ .NAME }}-service
spec:
  selector:
    app: {{ .NAME }}
  ports:
  - protocol: TCP
    port: 80
---
apiVersion: apps/v1beta1
kind: Deployment
metadata:
  name: {{ .NAME }}-deployment
spec:
  replicas: {{ .REPLICAS }}
  template: 
    metadata:
      labels:
        app: {{ .NAME }}
    spec:
      containers:
      - name: nginx
        image: nginx:1.7.9
        ports:
        - containerPort: 80

kubetpl render k8s/template.yml -i k8s/staging.env -s REPLICAS=3 should then yield

apiVersion: v1
kind: Service
metadata:
  name: sample-app-service
spec:
  selector:
    app: sample-app
  ports:
  - protocol: TCP
    port: 80
---
apiVersion: apps/v1beta1
kind: Deployment
metadata:
  name: sample-app-deployment
spec:
  replicas: 3
  template: 
    metadata:
      labels:
        app: sample-app
    spec:
      containers:
      - name: nginx
        image: nginx:1.7.9
        ports:
        - containerPort: 80

aka kind: Template.

As described in Templates + Parameterization proposal.

Let's say we have the following (click to expand):

NAME=sample-app

# kubetpl:syntax:template-kind

kind: Template
apiVersion: v1
metadata:
  name: nginx-template
  annotations:
    description: nginx template
objects:
- apiVersion: v1
  kind: Service
  metadata:
    name: $(NAME)-service
  spec:
    selector:
      app: $(NAME)
    ports:
    - protocol: TCP
      port: 80
- apiVersion: apps/v1beta1
  kind: Deployment
  metadata:
    name: $(NAME)-deployment
  spec:
    replicas: $((REPLICAS))
    template: 
      metadata:
        labels:
          app: $(NAME)
      spec:
        containers:
        - name: nginx
          image: nginx:1.7.9
          ports:
          - containerPort: 80
parameters:
- name: NAME
  description: Application name
  required: true
  parameterType: string
- name: REPLICAS
  description: Number of replicas
  value: 1
  required: true
  parameterType: int

kubetpl render k8s/template.yml -i k8s/staging.env -s REPLICAS=3 should then yield

apiVersion: v1
kind: Service
metadata:
  name: sample-app-service
spec:
  selector:
    app: sample-app
  ports:
  - protocol: TCP
    port: 80
---
apiVersion: apps/v1beta1
kind: Deployment
metadata:
  name: sample-app-deployment
spec:
  replicas: 3
  template: 
    metadata:
      labels:
        app: sample-app
    spec:
      containers:
      - name: nginx
        image: nginx:1.7.9
        ports:
        - containerPort: 80

PREREQUISITE: go1.9+.

git clone https://github.com/shyiko/kubetpl $GOPATH/src/github.com/shyiko/kubetpl 
cd $GOPATH/src/github.com/shyiko/kubetpl
make fetch

go run kubetpl.go

All code, unless specified otherwise, is licensed under the MIT license.
Copyright (c) 2018 Stanley Shyiko.