Function kube::runtime::reflector

pub fn reflector<K, W>(
    writer: Writer<K>,
    stream: W
) -> impl Stream<Item = <W as Stream>::Item>
where
    K: Lookup + Clone,
    <K as Lookup>::DynamicType: Eq + Hash + Clone,
    W: Stream<Item = Result<Event<K>, Error>>,

Available on crate feature runtime only.

Cache objects from a watcher() stream into a local Store

Observes the raw Stream of watcher::Event objects, and modifies the cache. It passes the raw watcher() stream through unmodified.

Usage

Create a Store through e.g. store::store(). The writer part is not-clonable, and must be moved into the reflector. The reader part is the Store interface that you can send to other parts of your program as state.

The cache contains the last-seen state of objects, which may lag slightly behind the actual state.

Example

Infinite watch of Node resources with a certain label.

The reader part being passed around to a webserver is omitted. For examples see version-rs for integration with axum, or controller-rs for the similar controller integration with actix-web.

use k8s_openapi::api::core::v1::Node;
use kube::runtime::{reflector, watcher, WatchStreamExt, watcher::Config};
use futures::{StreamExt, future::ready};

let nodes: Api<Node> = Api::all(client);
let node_filter = Config::default().labels("kubernetes.io/arch=amd64");
let (reader, writer) = reflector::store();

// Create the infinite reflector stream
let rf = reflector(writer, watcher(nodes, node_filter));

// !!! pass reader to your webserver/manager as state !!!

// Poll the stream (needed to keep the store up-to-date)
let infinite_watch = rf.applied_objects().for_each(|o| { ready(()) });
infinite_watch.await;

Memory Usage

A reflector often constitutes one of the biggest components of a controller’s memory use. Given a ~2000 pods cluster, a reflector saving everything (including injected sidecars, managed fields) can quickly consume a couple of hundred megabytes or more, depending on how much of this you are storing.

While generally acceptable, there are techniques you can leverage to reduce the memory usage depending on your use case.

1. Reflect a PartialObjectMeta<K> stream rather than a stream of K

You can send in a metadata_watcher() for a type rather than a watcher(), and this can drop your memory usage by more than a factor of two, depending on the size of K. 60% reduction seen for Pod. Usage is otherwise identical.

2. Use modify the raw watcher::Event object stream to clear unneeded properties

For instance, managed fields typically constitutes around half the size of ObjectMeta and can often be dropped:

let stream = watcher(api, Default::default()).map_ok(|ev| {
    ev.modify(|pod| {
        pod.managed_fields_mut().clear();
        pod.annotations_mut().clear();
        pod.status = None;
    })
});

The stream can then be passed to reflector causing smaller objects to be written to its store. Note that you cannot drop everything; you minimally need the spec properties your app relies on. Additionally, only labels, annotations and managed_fields are safe to drop from ObjectMeta.

For more information check out: https://kube.rs/controllers/optimization/ for graphs and techniques.