kube

Rust client for Kubernetes with reinterpretations of the Reflector and Informer abstractions from the go client.

This client thus aims cater to the more common controller/operator case, but allows you sticking in dependencies like k8s-openapi for accurate struct representations.

Usage

See the examples directory for how to watch over resources in a simplistic way.

See controller-rs for a full example with actix.

Reflector

The biggest abstraction exposed in this client is Reflector<T, U>. This is effectively a cache of a resource that's meant to "reflect the state in etcd".

It handles the api mechanics for watching kube resources, tracking resourceVersions, and maintaining an internal cache map.

To use it, you just feed in T as a Spec struct and U as a Status struct, which can be as complete or incomplete as you like. Here, using the complete structs via k8s-openapi:

use k8s_openapi::api::core::v1::{PodSpec, PodStatus};
let resource = ResourceType::Pods(Some("kube-system".into()));
let rf : Reflector<PodSpec, PodStatus> = Reflector::new(client.clone(), resource.into())?;

then you can poll() the reflector, and read() to get the current cached state:

rf.poll()?; // blocks and updates state

// read state and use it:
rf.read()?.into_iter().for_each(|(name, p)| {
    println!("Found pod {} ({}) with {:?}",
        name,
        p.status.phase.unwrap(),
        p.spec.containers.into_iter().map(|c| c.name).collect::<Vec<_>>(),
    );
});

The reflector itself is responsible for acquiring the write lock and update the state as long as you call poll() periodically.

Informers

The simplest abstraction exposed from this client. This is a struct with the internal behaviour for watching kube resources, but keeps no internal state except the resourceVersion.

You tell it what type parameters correspond to; T should be a Spec struct, and U should be a Status struct. Again, these can be as complete or incomplete as you like. Here, using the complete structs via k8s-openapi:

use k8s_openapi::api::core::v1::{PodSpec, PodStatus};
let resource = ResourceType::Pods(Some("kube-system".into()));
let inf : Informer<PodSpec, PodStatus> = Informer::new(client.clone(), resource.into())?;

The main difference with Reflector<T, U> is that the only exposed function is .poll() and it returns WatchEvents that you are meant to handle yourself:

let events = inf.poll()?;
reconcile(&client, events)?; // pass them on somewhere

How you handle them is up to you, you could build your own Reflector, or you can do more controllery logic. Here's how such a function would look:

fn reconcile(_c: &APIClient, events: WatchEvents<PodSpec, PodStatus>) -> Result<(), failure::Error> {
    for ev in events {
        // TODO: Use the kube api client here..
        match ev {
            WatchEvent::Added(o) => {
                let containers = o.spec.containers.into_iter().map(|c| c.name).collect::<Vec<_>>();
                info!("Added Pod: {} (containers={:?})", o.metadata.name, containers);
            },
            WatchEvent::Modified(o) => {
                let phase = o.status.phase.unwrap();
                info!("Modified Pod: {} (phase={})", o.metadata.name, phase);
            },
            WatchEvent::Deleted(o) => {
                info!("Deleted Pod: {}", o.metadata.name);
            },
            WatchEvent::Error(e) => {
                warn!("Error event: {:?}", e);
            }
        }
    }
    Ok(())
}

Examples

Examples that show a little common flows. These all have logging of this library set up to trace:

# watch pod events in kube-system
cargo run --example pod_informer

or for the reflectors:

cargo run --example pod_reflector
cargo run --example node_reflector
cargo run --example deployment_reflector

for one based on a CRD, you need to create the CRD first:

kubectl apply -f examples/foo.yaml
cargo run --example crd_reflector

then you can kubectl apply -f crd-baz.yaml -n kube-system, or kubectl delete -f crd-baz.yaml -n kube-system, or kubectl edit foos baz -n kube-system to verify that the events are being picked up.

License