- Background
- SDK CLI installation and app-operator example
- Project Scaffolding Layout
- Example app-operator code layout
- Reference link
Background
Operator concept is introduced to k8s community at 2016,
An Operator is an application-specific controller that extends the Kubernetes API to create, configure, and manage instances of complex stateful applications on behalf of a Kubernetes user. It builds upon the basic Kubernetes resource and controller concepts but includes domain or application-specific knowledge to automate common tasks.
Operator SDK is a framework to make writing operators easier. Which provides:
- High level APIs and abstractions to write the operational logic more intuitively
- Tools for scaffolding and code generation to bootstrap a new project fast
- Extensions to cover common operator use cases
SDK CLI installation and app-operator example
Follow the guide from “Quick Start”: https://github.com/operator-framework/operator-sdk#quick-start
Project Scaffolding Layout
The operator-sdk CLI generates a number of packages for each project. The following table describes a basic rundown of each generated file/directory.
| File/Folders | Purpose |
|---|---|
| cmd | Contains manager/main.go which is the main program of the operator. This instantiates a new manager which registers all custom resource definitions under pkg/apis/... and starts all controllers under pkg/controllers/... . |
| pkg/apis | Contains the directory tree that defines the APIs of the Custom Resource Definitions(CRD). Users are expected to edit the pkg/apis/<group>/<version>/<kind>_types.go files to define the API for each resource type and import these packages in their controllers to watch for these resource types. |
| pkg/controller | This pkg contains the controller implementations. Users are expected to edit the pkg/controller/<kind>/<kind>_controller.go to define the controller’s reconcile logic for handling a resource type of the specified kind. |
| build | Contains the Dockerfile and build scripts used to build the operator. |
| deploy | Contains various YAML manifests for registering CRDs, setting up RBAC, and deploying the operator as a Deployment. |
| (Gopkg.toml Gopkg.lock) or (go.mod go.sum) | The Go mod or Go Dep manifests that describe the external dependencies of this operator, depending on the dependency manager chosen when initializing or migrating a project. |
| vendor | The golang vendor folder that contains the local copies of the external dependencies that satisfy the imports of this project. Go Dep/Go modules manages the vendor directly. |
Example app-operator code layout
The code layout of example “app-operator”
Operator SDK generates lots of files/directories for developers, but most of the generated files/directories are not expected to edit.
Developers should focus on pkg/apis/<group>/<version>/<kind>_types.go and pkg/controller/<kind>/<kind>_controller.go.
Edit pkg/apis/<group>/<version>/<kind>_types.go to define the custom resource type, and edit pkg/controller/<kind>/<kind>_controller.go to define reconcile logic for custom resource.
Note: After modifying the pkg/apis/<group>/<version>/<kind>_types.go, developer should always run the following command to update the generated code for that resource type:
$ operator-sdk generate k8s