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Quack

NOTE: this repository is currently UNMAINTAINED and is looking for new owner(s). See #19 for more information.

In-Cluster templating using the Go Template syntax.

Note: This is a proof of concept in the early alpha stage. We are providing no guarantees. We also cannot provide support for Kubernetes configuration, Mutating Webhooks are currently beta and the required configuration is complex. Please see the Installation section for further detail.

Table of contents

Introduction

Client Side templating can be error prone. When running multiple Kubernetes clusters it can be very easy to apply rendered templates to the wrong cluster.

Quack solves this problem by rendering the templates as they are applied to the cluster.

Quack acts as a Mutating Webhook Admission Controller and intercepts requests to create and update Kubernetes resources such as Deployments, Ingresses and ConfigMaps.

Any resource that contains Go Template syntax will be templated (using values from Quack's ConfigMap) before it passes through API validation.

Quack is ideal for templating Cluster-wide environment such as the Cluster Name, Region and Environment (Staging/Production).

Installation

Deploying to Kubernetes

Example Kubernetes manifests are in the deploy folder.

Quack RBAC

Quack uses RBAC to ensure that requests for templating are authorized. If you are running RBAC within your Kubernetes cluster you must ensure that you configure Webhook Authentication in your Kubernetes API server. See the docs.

Once you have configured the API server authentication, ensure you update the API Server ClusterRoleBinding with the appropriate subject.

Certificates

Quack requires a TLS certificate for serving the webhook securely. This certificate must be signed by a CA certificate.

In Kubernetes 1.9, Webhooks must be called over HTTPS and the serving certificate's CA bundle must be configured in the MutatingWebhookConfiguration. This establishes trust between the API server and Quack.

Base64 encode your CA certificate bundle and substitute it for the caBundle field in the MutatingWebhookConfiguration.

The example Daemonset expects a secret containing the certificate in the format as below:

apiVersion: v1
data:
  cert.pem: <BASE64_ENCODED_CERTIFICATE>
  key.pem: <BASE64_ENCODED_PRIVATE_KEY>
kind: Secret
metadata:
  name: quack-certs
  namespace: quack
type: Opaque

Configuration

Quack adopts the standard Kubernetes Generic API server flags (including Authentication and Authorization flags). It loads the In Cluster configuration by default but this can be overridden by the --kubeconfig flag.

Quack takes the following additional flags:

  • --values-configmap (Default: quack-values): Defines the name of the ConfigMap to load cluster level template values from.
  • --values-configmap-namespace (Default: quack): Defines the namespace in which the Values ConfigMap exists.
  • --required-annotation: Filter objects based on the existence of a named annotation before templating them.
  • --ignore-path: Ignore patches for certain paths in when templating files. May be called multiple times. Paths should be specified as RFC6901 JSON Pointers.

Restricting Quack

You should configure Quack to only template the resources you need it to template.

There are three parts to restricting Quack:

Namespace

A Namespace selector in the MutatingWebhookConfiguration must be matched for resources within the Namespace to be templated by Quack.

apiVersion: v1
kind: Namespace
metadata:
  name: kube-system
  labels:
    quack.pusher.com/enabled: "true"
Resource rules

A list of resoucre rules in the MutatingWebhookConfiguration must be matched for resources to be templated by Quack.

Add and remove resources to fit your requirements:

rules:
  - operations: ["CREATE", "UPDATE"]
    apiGroups: ["*"]
    apiVersions: ["*"]
    resources:
      - configmaps
      - daemonsets
      - deployments
      - statefulsets
      - ingresses
      - services
Required annotation

Using the flag --required-annotation, you can tell Quack to skip templating for any resource not annotated appropriately.

For example, if Quack is configured with --required-annotation=quack.pusher.com/template, only resources (matching the Resource rules and Namespace Selector) with an annotation as below will be templated:

---
apiVersion: v1
metadata:
  annotations:
    quack.pusher.com/template: "true" # The value is not checked.

Example Quack Template

In this example, we are defining an Ingress object for the Kubernetes Dashboard.

We suppose that there is an existing Kubernetes cluster known as alpha. We then assume that Quack is configured to watch the Namespace kube-system and that a DNS record for alpha.example.com points to the Ingress Controller on the Kubernetes cluster alpha.

In this case, the Quack installation might have the ConfigMap:

apiVersion: v1
kind: ConfigMap
metadata:
  name: quack-values
  namespace: quack
data:
  ClusterName: alpha

Create the Ingress object as below and apply it to the cluster:

kubectl apply -f ingress.yaml

ingress.yaml:

apiVersion: extensions/v1beta1
kind: Ingress
metadata:
  name: kubernetes-dashboard
  namespace: kube-system
spec:
  tls:
    - hosts:
        - "{{- .ClusterName -}}.example.com"
  rules:
    - host: "{{- .ClusterName -}}.example.com"
      http:
        paths:
          - path: /ui
            backend:
              serviceName: kubernetes-dashboard
              servicePort: 443

Once applied, fetch the Ingress object to see that it has been templated appropriately by Quack:

kubectl get -f ingress.yaml -o yaml
apiVersion: extensions/v1beta1
kind: Ingress
metadata:
  name: kubernetes-dashboard
  namespace: kube-system
spec:
  tls:
    - hosts:
        - "alpha.example.com"
  rules:
    - host: "alpha.example.com"
      http:
        paths:
          - path: /ui
            backend:
              serviceName: kubernetes-dashboard
              servicePort: 443

When creating further Kubernetes clusters, the same template can be applied directly to each cluster and the resulting Kubernetes resources will be correct for their cluster's particular environment.

Custom Delimiters

Each individual Quack template can specify their own delimiters for use against the template.

Add annotations quack.pusher.com/left-delim and quack.pusher.com/right-delim to your template with the desired left and right template delimiters respectively.

---
apiVersion: v1
metadata:
  annotations:
    quack.pusher.com/left-delim: "[["
    quack.pusher.com/right-delim: "]]"
...
spec:
  foo: "[[- .FooValue -]]"

Quack vs Other Systems

  • Quack intercepts the standard flow of kubectl apply. This means there are no extra tools and no additional syntax to learn, bar the Go Templating Syntax.
  • Resources are still created using the main Kubernetes API server. This means that regular syntax validation and Authorization still happen as the object is being created or updated.
  • Cluster specific values are stored in cluster and separate from your templates. Allows you to keep one copy of Kubernetes manifests and reuse them across all clusters without any client side changes.
  • Protects against mistakenly applying manifests cross clusters. (Templates have no specific configuration for each cluster, Quack abstracts this.)

Communication

  • Found a bug? Please open an issue.
  • Have a feature request. Please open an issue.
  • If you want to contribute, please submit a pull request

Contributing

Please see our Contributing guidelines.

License

This project is licensed under Apache 2.0 and a copy of the license is available here.