cnat

Cloud Native at, runs command at schedule by creating a Pod.

apiVersion: example.kazk.dev/v1alpha1
kind: At
metadata:
  name: example
spec:
  schedule: "2020-12-17T19:21:00Z"
  command: [echo, "will be executed"]

Example Kubernetes controller programming-kubernetes/cnat in Rust using kube.

Changes

• Changed command to an array
• Removed Pending from status.phase. None -> Running -> Done
• Changed to use apiextensions.k8s.io/v1 and added the required schema
  • The schema is generated by kube (clux/kube-rs#348)
  • schedule is validated as date-time

Generated CRD

apiVersion: apiextensions.k8s.io/v1
kind: CustomResourceDefinition
metadata:
  name: ats.example.kazk.dev
spec:
  group: example.kazk.dev
  names:
    kind: At
    plural: ats
    shortNames: []
    singular: at
  scope: Namespaced
  versions:
    - additionalPrinterColumns: []
      name: v1alpha1
      schema:
        openAPIV3Schema:
          description: "Auto-generated derived type for AtSpec via `CustomResource`"
          properties:
            spec:
              description: Spec for custom resource At.
              properties:
                command:
                  items:
                    type: string
                  type: array
                schedule:
                  format: date-time
                  type: string
              required:
                - command
                - schedule
              type: object
            status:
              description: Status for custom resource At.
              nullable: true
              properties:
                phase:
                  description: Describes the status of the scheduled command.
                  enum:
                    - Running
                    - Done
                  type: string
              required:
                - phase
              type: object
          required:
            - spec
          title: At
          type: object
      served: true
      storage: true
      subresources:
        status: {}

Project Structure

.
├── k8s/               CRD and example
└── src/
    ├── bin/           Binaries
    │   ├── cnat.rs    - Run controller (default-run)
    │   └── crd.rs     - Output CRD YAML
    ├── controller.rs  Implements the Controller
    ├── lib.rs
    └── resource.rs    Defines the Custom Resource

Commands

• cargo run: Run controller
• cargo run --bin crd: Output CRD

Running

Locally

# Create CRD
kubectl apply -f k8s/ats.yml
kubectl wait --for=condition=NamesAccepted crd/ats.example.kazk.dev

# Start controller
cargo run

# Create At resource example
kubectl apply -f k8s/example.yml

Inside

# Set up service account
kubectl apply -f k8s/rbac.yml

# Create CRD
kubectl apply -f k8s/ats.yml
kubectl wait --for=condition=NamesAccepted crd/ats.example.kazk.dev

# Deploy controller
kubectl apply -f k8s/deployment.yml

# Create At resource example
kubectl apply -f k8s/example.yml

Comparisons

Binary Size

Building on Arch Linux:

• client-go: 31MB (23MB with -ldflags "-s -w")
• kubebuilder: TBD requires unknown version of KubeBuilder
• operator-sdk: TBD requires unknown version of Operator SDK
• kube: 8.3MB (5.8MB with RUSTFLAGS='-C link-arg=-s')

Lines of Code

Library	Files	Lines	Code	Comments	Blanks
client-go	29	2161	1212	658	291
kubebuilder	16	1013	529	357	127
operator-sdk	13	714	488	134	92
kube	5	257	217	15	25

• client-go: tokei -e cnat-client-go/vendor -e cnat-client-go/hack -t Go cnat-client-go
• kubebuilder: tokei -e cnat-kubebuilder/vendor -e cnat-kubebuilder/hack -t Go cnat-kubebuilder
• operator-sdk: tokei -e cnat-operator/vendor -t Go cnat-operator
• kube: tokei -t Rust

Project Setup and Dependencies

• client-go: Go modules works fine (3 core modules + 1 code geerator + 1 logger). Versioning has improved since programming-kubernetes/cnat was written. A lot of generated code.
• kubebuilder: Requires KubeBuilder tool. Build failed with GOPATH not defined. Uses dep.
• operator-sdk: Requires Operator SDK tool. Haven't tried. Uses dep.
• kube: Standard Rust project. No separate codegen and very straightforward. CRD v1 schema is generated from the spec struct clux/kube-rs#348 :)

References

• ConfigMapGenerator example
• at_controller.go
• h2oai/h2o-kubernetes