Finalizer helper

examples/Cargo.toml

@@ -181,3 +181,7 @@ required-features = ["native-tls", "rustls-tls"]
 [[example]]
 name = "custom_client_trace"
 path = "custom_client_trace.rs"
+
+[[example]]
+name = "secret_syncer"
+path = "secret_syncer.rs"

examples/secret_syncer.rs

@@ -0,0 +1,109 @@
+// Demonstrates a controller some outside resource that it needs to clean up when the owner is deleted
+
+// NOTE: This is designed to demonstrate how to use finalizers, but is not in itself a good use case for them.
+// If you actually want to clean up other Kubernetes objects then you should use `ownerReferences` instead and let
+// k8s garbage collect the children.
+
+use futures::StreamExt;
+use k8s_openapi::api::core::v1::{ConfigMap, Secret};
+use kube::{
+    api::{DeleteParams, ListParams, ObjectMeta, Patch, PatchParams, Resource},
+    error::ErrorResponse,
+    Api,
+};
+use kube_runtime::{
+    controller::{Context, ReconcilerAction},
+    finalizer::{finalizer, Event},
+    Controller,
+};
+use snafu::{OptionExt, ResultExt, Snafu};
+use std::time::Duration;
+
+#[derive(Debug, Snafu)]
+enum Error {
+    NoName,
+    NoNamespace,
+    UpdateSecret { source: kube::Error },
+    DeleteSecret { source: kube::Error },
+}
+type Result<T, E = Error> = std::result::Result<T, E>;
+
+fn secret_name_for_configmap(cm: &ConfigMap) -> Result<String> {
+    Ok(format!("cm---{}", cm.metadata.name.as_deref().context(NoName)?))
+}
+
+async fn apply(cm: ConfigMap, secrets: &kube::Api<Secret>) -> Result<ReconcilerAction> {
+    println!("Reconciling {:?}", cm);
+    let secret_name = secret_name_for_configmap(&cm)?;
+    secrets
+        .patch(
+            &secret_name,
+            &PatchParams::apply("configmap-secret-syncer.nullable.se"),
+            &Patch::Apply(Secret {
+                metadata: ObjectMeta {
+                    name: Some(secret_name.clone()),
+                    ..ObjectMeta::default()
+                },
+                string_data: cm.data,
+                data: cm.binary_data,
+                ..Secret::default()
+            }),
+        )
+        .await
+        .context(UpdateSecret)?;
+    Ok(ReconcilerAction { requeue_after: None })
+}
+
+async fn cleanup(cm: ConfigMap, secrets: &kube::Api<Secret>) -> Result<ReconcilerAction> {
+    println!("Cleaning up {:?}", cm);
+    secrets
+        .delete(&secret_name_for_configmap(&cm)?, &DeleteParams::default())
+        .await
+        .map(|_| ())
+        .or_else(|err| match err {
+            // Object is already deleted
+            kube::Error::Api(ErrorResponse { code: 404, .. }) => Ok(()),
+            err => Err(err),
+        })
+        .context(DeleteSecret)?;
+    Ok(ReconcilerAction { requeue_after: None })
+}
+
+#[tokio::main]
+async fn main() -> color_eyre::Result<()> {
+    env_logger::init();
+    let kube = kube::Client::try_default().await?;
+    let all_cms = kube::Api::<ConfigMap>::all(kube.clone());
+    Controller::new(
+        all_cms,
+        ListParams::default().labels("configmap-secret-syncer.nullable.se/sync=true"),
+    )
+    .run(
+        |cm, _| {
+            let ns = cm.meta().namespace.as_deref().context(NoNamespace).unwrap();
+            let cms: Api<ConfigMap> = Api::namespaced(kube.clone(), ns);
+            let secrets: Api<Secret> = Api::namespaced(kube.clone(), ns);
+            async move {
+                finalizer(
+                    &cms,
+                    "configmap-secret-syncer.nullable.se/cleanup",
+                    cm,
+                    |event| async {
+                        match event {
+                            Event::Apply(cm) => apply(cm, &secrets).await,
+                            Event::Cleanup(cm) => cleanup(cm, &secrets).await,
+                        }
+                    },
+                )
+                .await
+            }
+        },
+        |_err, _| ReconcilerAction {
+            requeue_after: Some(Duration::from_secs(2)),
+        },
+        Context::new(()),
+    )
+    .for_each(|msg| async move { println!("Reconciled: {:?}", msg) })
+    .await;
+    Ok(())
+}

examples/secret_syncer_configmap.yaml

@@ -0,0 +1,9 @@
+apiVersion: v1
+kind: ConfigMap
+metadata:
+  name: secret-syncer-example
+  labels:
+    configmap-secret-syncer.nullable.se/sync: "true"
+data:
+  foo: bar
+  spam: eggs

kube-runtime/Cargo.toml

@@ -14,7 +14,7 @@ edition = "2018"
 
 [dependencies]
 futures = "0.3.8"
-kube = { path = "../kube", version = "^0.57.0", default-features = false, features = ["client"] }
+kube = { path = "../kube", version = "^0.57.0", default-features = false, features = ["jsonpatch", "client"] }
 derivative = "2.1.1"
 serde = "1.0.118"
 smallvec = "1.6.0"
@@ -24,6 +24,8 @@ snafu = { version = "0.6.10", features = ["futures"] }
 dashmap = "4.0.1"
 tokio-util = { version = "0.6.0", features = ["time"] }
 tracing = "0.1.26"
+json-patch = "0.2.6"
+serde_json = "1.0.64"
 
 [dependencies.k8s-openapi]
 version = "0.12.0"

kube-runtime/src/finalizer.rs

@@ -0,0 +1,210 @@
+use crate::controller::ReconcilerAction;
+use futures::{TryFuture, TryFutureExt};
+use json_patch::{AddOperation, PatchOperation, RemoveOperation, TestOperation};
+use kube::{
+    api::{Patch, PatchParams},
+    Api, Resource,
+};
+use serde::{de::DeserializeOwned, Serialize};
+use snafu::{OptionExt, ResultExt, Snafu};
+use std::{error::Error as StdError, fmt::Debug};
+
+#[derive(Debug, Snafu)]
+pub enum Error<ReconcileErr>
+where
+    ReconcileErr: StdError + 'static,
+{
+    #[snafu(display("failed to apply object: {}", source))]
+    ApplyFailed { source: ReconcileErr },
+    #[snafu(display("failed to clean up object: {}", source))]
+    CleanupFailed { source: ReconcileErr },
+    #[snafu(display("failed to add finalizer: {}", source))]
+    AddFinalizer { source: kube::Error },
+    #[snafu(display("failed to remove finalizer: {}", source))]
+    RemoveFinalizer { source: kube::Error },
+    #[snafu(display("object has no name"))]
+    UnnamedObject,
+}
+
+struct FinalizerState {
+    finalizer_index: Option<usize>,
+    is_deleting: bool,
+}
+
+impl FinalizerState {
+    fn for_object<K: Resource>(obj: &K, finalizer_name: &str) -> Self {
+        Self {
+            finalizer_index: obj
+                .meta()
+                .finalizers
+                .iter()
+                .enumerate()
+                .find(|(_, fin)| *fin == finalizer_name)
+                .map(|(i, _)| i),
+            is_deleting: obj.meta().deletion_timestamp.is_some(),
+        }
+    }
+}
+
+/// Reconcile an object in a way that requires cleanup before an object can be deleted. It does this by
+/// managing a [`ObjectMeta::finalizers`] entry, which prevents the object from being deleted before the
+/// cleanup is done.
+///
+/// In typical usage, if you use `finalizer` then it should be the only top-level "action"
+/// in your [`applier`]/[`Controller`]'s `reconcile` function.
+///
+/// # Expected Flow
+///
+/// 1. User creates object
+/// 2. Reconciler sees object
+/// 3. `finalizer` adds `finalizer_name` to [`ObjectMeta::finalizers`]
+/// 4. Reconciler sees updated object
+/// 5. `finalizer` runs [`Event::Apply`]
+/// 6. User updates object
+/// 7. Reconciler sees updated object
+/// 8. `finalizer` runs [`Event::Apply`]
+/// 9. User deletes object
+/// 10. Reconciler sees deleting object
+/// 11. `finalizer` runs [`Event::Cleanup`]
+/// 12. `finalizer` removes `finalizer_name` from [`ObjectMeta::finalizers`]
+/// 13. Kubernetes sees that all [`ObjectMeta::finalizers`] are gone and finally deletes the object
+///
+/// # Guarantees
+///
+/// If [`Event::Apply`] is ever started then [`Event::Cleanup`] must succeed before the Kubernetes object deletion completes.
+///
+/// # Assumptions
+///
+/// `finalizer_name` must be unique among the controllers interacting with the object
+///
+/// [`Event::Apply`] and [`Event::Cleanup`] must both be idempotent, and tolerate being executed several times (even if previously cancelled).
+///
+/// [`Event::Cleanup`] must tolerate [`Event::Apply`] never having ran at all, or never having succeeded. Keep in mind that
+/// even infallible `.await`s are cancellation points.
+///
+/// # Caveats
+///
+/// Object deletes will get stuck while the controller is not running, or if `cleanup` fails for some reason.
+///
+/// `reconcile` should take the object that the [`Event`] contains, rather than trying to reuse `obj`, since it may have been updated.
+///
+/// # Errors
+///
+/// [`Event::Apply`] and [`Event::Cleanup`] are both fallible, their errors are passed through as [`Error::ApplyFailed`]
+/// and [`Error::CleanupFailed`], respectively.
+///
+/// In addition, adding and removing the finalizer itself may fail. In particular, this may be because of
+/// network errors, lacking permissions, or because another `finalizer` was updated in the meantime on the same object.
+pub async fn finalizer<K, ReconcileFut>(
+    api: &Api<K>,
+    finalizer_name: &str,
+    obj: K,
+    reconcile: impl FnOnce(Event<K>) -> ReconcileFut,
+) -> Result<ReconcilerAction, Error<ReconcileFut::Error>>
+where
+    K: Resource + Clone + DeserializeOwned + Serialize + Debug,
+    ReconcileFut: TryFuture<Ok = ReconcilerAction>,
+    ReconcileFut::Error: StdError + 'static,
+{
+    match FinalizerState::for_object(&obj, finalizer_name) {
+        FinalizerState {
+            finalizer_index: Some(_),
+            is_deleting: false,
+        } => reconcile(Event::Apply(obj))
+            .into_future()
+            .await
+            .context(ApplyFailed),
+        FinalizerState {
+            finalizer_index: Some(finalizer_i),
+            is_deleting: true,
+        } => {
+            // Cleanup reconciliation must succeed before it's safe to remove the finalizer
+            let name = obj.meta().name.clone().context(UnnamedObject)?;
+            let action = reconcile(Event::Cleanup(obj))
+                .into_future()
+                .await
+                // Short-circuit, so that we keep the finalizer if cleanup fails
+                .context(CleanupFailed)?;
+            // Cleanup was successful, remove the finalizer so that deletion can continue
+            let finalizer_path = format!("/metadata/finalizers/{}", finalizer_i);
+            api.patch::<K>(
+                &name,
+                &PatchParams::default(),
+                &Patch::Json(json_patch::Patch(vec![
+                    // All finalizers run concurrently and we use an integer index
+                    // `Test` ensures that we fail instead of deleting someone else's finalizer
+                    // (in which case a new `Cleanup` event will be sent)
+                    PatchOperation::Test(TestOperation {
+                        path: finalizer_path.clone(),
+                        value: finalizer_name.into(),
+                    }),
+                    PatchOperation::Remove(RemoveOperation { path: finalizer_path }),
+                ])),
+            )
+            .await
+            .context(RemoveFinalizer)?;
+            Ok(action)
+        }
+        FinalizerState {
+            finalizer_index: None,
+            is_deleting: false,
+        } => {
+            // Finalizer must be added before it's safe to run an `Apply` reconciliation
+            let patch = json_patch::Patch(if obj.meta().finalizers.is_empty() {
+                vec![
+                    PatchOperation::Test(TestOperation {
+                        path: "/metadata/finalizers".to_string(),
+                        value: serde_json::Value::Null,
+                    }),
+                    PatchOperation::Add(AddOperation {
+                        path: "/metadata/finalizers".to_string(),
+                        value: vec![finalizer_name].into(),
+                    }),
+                ]
+            } else {
+                vec![PatchOperation::Add(AddOperation {
+                    path: "/metadata/finalizers/-".to_string(),
+                    value: finalizer_name.into(),
+                })]
+            });
+            api.patch::<K>(
+                obj.meta().name.as_deref().context(UnnamedObject)?,
+                &PatchParams::default(),
+                &Patch::Json(patch),
+            )
+            .await
+            .context(AddFinalizer)?;
+            // No point applying here, since the patch will cause a new reconciliation
+            Ok(ReconcilerAction { requeue_after: None })
+        }
+        FinalizerState {
+            finalizer_index: None,
+            is_deleting: true,
+        } => {
+            // Our work here is done
+            Ok(ReconcilerAction { requeue_after: None })
+        }
+    }
+}
+
+/// A representation of an action that should be taken by a reconciler.
+pub enum Event<K> {
+    /// The reconciler should ensure that the actual state matches the state desired in the object.
+    ///
+    /// This must be idempotent, since it may be recalled if, for example (this list is non-exhaustive):
+    ///
+    /// - The controller is restarted
+    /// - The object is updated
+    /// - The reconciliation fails
+    /// - The grinch attacks
+    Apply(K),
+    /// The object is being deleted, and the reconciler should remove all resources that it owns.
+    ///
+    /// This must be idempotent, since it may be recalled if, for example (this list is non-exhaustive):
+    ///
+    /// - The controller is restarted while the deletion is in progress
+    /// - The reconciliation fails
+    /// - Another finalizer was removed in the meantime
+    /// - The grinch's heart grows a size or two
+    Cleanup(K),
+}

kube-runtime/src/lib.rs

@@ -18,12 +18,14 @@
 #![allow(clippy::type_repetition_in_bounds)]
 
 pub mod controller;
+pub mod finalizer;
 pub mod reflector;
 pub mod scheduler;
 pub mod utils;
 pub mod watcher;
 
 pub use controller::{applier, Controller};
+pub use finalizer::finalizer;
 pub use reflector::reflector;
 pub use scheduler::scheduler;
 pub use watcher::watcher;