kTailor

In modern Kubernetes environments, developers often need to inject standard infrastructure components into their applications like monitoring sidecars, proxy configurations, or specific environment variables. In our case we needed to add an initContainer to inject libfaketime into the pods which enables the containers to travel through time.

Instead of cluttering every single Deployment manifest, we built a lightweight Kubernetes Mutating Webhook that centralizes these modifications: kTailor. It's designed to dynamically modify Deployments without altering the original source manifests. The configuration is stored in simple, reusable ConfigMaps, where the essential infrastructure components to inject (like initContainers, sidecars, environment variables and volumes) are defined using the common kubernetes markup.

Key Features

• Adheres to KISS Principle: Designed to keep it smart and simple, ensuring efficient deployment modifications.
• Small & Fast: Built in Go, kTailor utilizes an efficient In-Memory Informer Cache, delivering near-zero latency.
• Targeted Efficiency: Applies changes solely to Deployments with specific trigger labels, ignoring the rest.
• User-Friendly Templates: Templates can be defined using standard Kubernetes-like YAML, eliminating the need for complex programming languages.

When to Use kTailor

kTailor is ideal for scenarios requiring standard modifications, such as adding monitoring sidecars or environment variables. However, it is not suited for complex policy enforcement or validations beyond standard Deployments. For those needs, consider other established policy engines like Kyverno or OPA Gatekeeper.

Template Management and Triggering

Templates in kTailor are managed as standard Kubernetes ConfigMaps. To activate a template, the Deployment must feature the ktailor.dev/fit label pointing to the template name:

kubectl label --overwrite deployment myapp ktailor.dev/fit="local.ktlr-proxy-tmpl"

Practical Examples

1. Insert Environment Variable

Inject an environment variable into an existing container with a simple central template:

apiVersion: v1
kind: ConfigMap
metadata:
  name: ktailor-test
  namespace: ktailor
  labels:
    ktailor.dev/template: "true"
data:
  template: |
    kind: ktailor-template
    modifyContainers:
      insertOrOverwrite:
        env:
          - name: KTAILORTEST
            value: "Env set by central kTailor template."

2. Advanced Time Manipulation

Utilizing libfaketime, kTailor can manipulate system time for a specific container while keeping the actual node time unchanged. This template includes shared volumes and an InitContainer setup:

apiVersion: v1
kind: ConfigMap
metadata:
  name: lft-plus222d
  namespace: ktailor
  labels:
    ktailor.dev/template: "true"
data:
  template: |
    kind: ktailor-template
    modifyContainers:
      insertIfNotExists:
        volumeMounts:
          - name: shared-lft-volume
            mountPath: /lft_volume
      insertOrOverwrite:
        env:
          - name: FAKETIME
            value: "+222d"
      setOrAppend:
        env:
          - name: LD_PRELOAD
            value: "/lft_volume/libfaketime.so.1"

    addInitContainers:
      - name: inject-libfaketime
        image: katalytic/libfaketime_init:1.0
        env:
          - name: LFT_DESTPATH
            value: /lft_volume
        volumeMounts:
        - name: shared-lft-volume
          mountPath: /lft_volume

    addVolumes:
      volumes:
        - name: shared-lft-volume
          emptyDir: {}

Explore kTailor and try it online at killercoda.com. For comprehensive documentation, visit ktailor.dev. This repository enhances the deployment experience within Kubernetes, streamlining the addition of necessary components efficiently.