You can extend Kubernetes with your own custom objects, but before you can do that you will need create a Custom Resource Definition so that Kubernetes knows what the object is allowed to look like. In this post I will create a very simple Kubernetes CRD for a Book kind using Rust and kube-rs.

Start by initiating a new Rust package.

cargo init book-crd

Add below dependencies to the cargo.toml file.

kube = { version = "0.83.0", features = ["runtime", "derive"] }
k8s-openapi = { version = "0.18.0", features = ["v1_26"] }
serde = "1.0.155"
serde_derive = "1.0.155"
serde_json = "1.0.94"
serde_yaml = "0.9.19"
schemars = "0.8.12"

Moving on to main.rs, add the nessacary libraries to the top of the file.

#[macro_use]
extern crate serde_derive;
use kube::{CustomResource, CustomResourceExt};
use schemars::JsonSchema;

Create a BookSpec struct with your desired properties. If you are reading this post you are probably already familiar with Kubernetes, I will not go into details with the kube properties, they are pretty self-explanatory.

#[derive(CustomResource, Debug, Serialize, Deserialize, Default, Clone, JsonSchema)]
#[kube(group = "linuxblog.xyz", version = "v1", kind = "Book", namespaced)]
#[kube(status = "BookStatus")]
pub struct BookSpec {
    pub title: String,
    pub authors: Option<Vec<String>>,
    pub isbn: u16,
}

Adding a Status spec is optional.

#[derive(Deserialize, Serialize, Clone, Debug, Default, JsonSchema)]
pub struct BookStatus {
    pub is_ok: bool,
    pub is_synced: bool,
}

In the main function print out the Book CRD.

fn main() {
    println!("{}", serde_yaml::to_string(&Book::crd()).unwrap());
}

That is it. Do a cargo run and it will print out the Custom Resource Definition as YAML.

References

• Kube Derive Custom Resource (opens new window)

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