Release 5.6 blog post

docs/content/en/blog/releases/v5-6-release.md

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+---
+title: Version 5.6 Released!
+date: 2026-08-28
+author: >-
+  [Attila Mészáros](https://github.com/csviri)
+---
+
+We're pleased to announce the release of Java Operator SDK v5.6.0! The headline features of this
+minor version are **informer pooling** — informers are now shared between controllers and event
+sources instead of one per event source — and a first-class **event recorder** for writing Kubernetes
+events. There are **no breaking API changes**.
+
+## Key Features
+
+### Informer pooling: shared informers across controllers
+
+Until now every `InformerEventSource` created its own `SharedIndexInformer`. An operator whose
+controllers all watch the same secondary type — `ConfigMap` and `Secret` being the usual suspects —
+opened one watch connection and kept one full cache **per controller** for the very same resources.
+
+Informers are now handed out by an `InformerPool` obtained from the `ConfigurationService`. Event
+sources whose effective informer configuration is equivalent are backed by a single informer, which
+cuts both memory usage and the number of watch connections opened against the API server. Two event
+sources share an informer when they match on all of:
+
+- the `KubernetesClient` they watch through, compared **by instance** (two clients are never
+  considered equivalent even when they point at the same API server — they may differ in
+  credentials, impersonation or TLS material),
+- the resource type, or the group/version/kind for generic resources,
+- the watched namespace,
+- the label, field and shard selectors,
+- the configured item store.
+
+Two things are deliberately *not* part of that identity. The `informerListLimit` is excluded, so
+event sources that disagree only on it still share an informer, keeping the limit of whichever one
+created it and logging a warning. Indexers are excluded because they can be added to a running
+informer: they are registered under a name qualified with the controller and event source that added
+them, so index names stay private to an event source and cannot collide, and they are removed again
+when that event source releases the informer. You keep looking indexes up by the name you
+registered.
+
+The pool is reference counted: the informer is created on first use and stopped only once the last
+event source using it is de-registered (or its controller stops). Registering an event source
+dynamically against an already running shared informer needs no special handling — the cache
+contents are replayed to the newly added handler.
+
+Two strategies ship, and both are selected through the `ConfigurationService`:
+
+```java
+// opt out of sharing, restoring the pre-5.6 behavior of one informer per event source
+Operator operator = new Operator(overrider ->
+    overrider.withInformerPool(new NonSharingInformerPool()));
+```
+
+`DefaultInformerPool` shares as described above and is the default; `NonSharingInformerPool` creates
+a dedicated informer per event source. A custom strategy extends `AbstractInformerPool`, which
+already creates the informers from an `InformerClassifier`, starts them and waits for their caches to
+sync, leaving the subclass only the question of whether and when an informer is shared.
+
+> **Note on stability**: the pooling itself is production ready, but the configuration API around it
+> (`ConfigurationService#informerPool`, `withInformerPool`) is marked `@Experimental` and may still
+> change in a non-backwards-compatible way.
+
+See the [eventing documentation](/docs/documentation/eventing) for details.
+
+### Kubernetes event recorder
+
+JOSDK now knows how to record Kubernetes events, so that a reconciler can surface what it is doing
+where users already look for it — `kubectl describe`. Inside a reconciliation the recorder is
+available from the `Context`, already bound to the primary resource:
+
+```java
+@Override
+public UpdateControl<MyResource> reconcile(MyResource resource, Context<MyResource> context) {
+  context.eventRecorder().normal("Reconciled", "resource reconciled");
+  context.eventRecorder().warn("SomethingIsOff", "this is a warning about the resource");
+  return UpdateControl.noUpdate();
+}
+```
+
+For more control, build an `EventRecord`, which also carries an optional action, reporting component,
+labels and annotations:
+
+```java
+context.eventRecorder().record(EventRecord.builder()
+    .type(EventType.WARNING)
+    .reason("DeploymentFailed")
+    .message("could not scale the deployment")
+    .action("Scaling")
+    .build());
+```
+
+Outside of the reconciliation loop — from a status listener or a background task, or about an object
+other than the primary — use the unbound form from
+`RegisteredController#eventRecorder()`, which is scoped to the controller rather than to a
+reconciliation:
+
+```java
+EventRecorder recorder = registeredController.eventRecorder();
+recorder.record(someOtherResource, EventRecord.normal("Noticed", "something happened"));
+```
+
+Two properties are worth calling out:
+
+- **Recording is best effort.** A failure to write the event is logged and swallowed, and never fails
+  the caller — a controller that fails to reconcile because it could not write an event is strictly
+  worse than one that records nothing.
+- **Repeats are aggregated, not duplicated.** Events are named deterministically, after the object
+  they are about plus a hash of everything that identifies the event. Recording the same event again
+  therefore resolves to the event already recorded and patches its `count` and `lastTimestamp`, which
+  is what makes `kubectl describe` report a repeating event once as `(x12 over 3m)` instead of
+  filling the event list with copies. Use `EventRecord.Builder#key(...)` to control what counts as
+  "the same" event.
+
+Events live in a namespace of their own: that of the object they are about, and for cluster scoped
+objects the namespace configured via `withClusterScopedEventNamespace(...)` or the
+`josdk.events.cluster-scoped-namespace` property, defaulting to `default`.
+
+Recording needs `get`, `create` and `patch` on `events` in the core (`""`) API group — all three,
+since an event is looked up before it is created and patched when it already exists. The generic Helm
+chart's `ClusterRole` grants them out of the box. If you write your own RBAC, note that a namespaced
+`Role` has to grant the permission in *every* namespace events are recorded in, including the
+cluster-scoped event namespace.
+
+Thanks to [Tan Qi](https://github.com/TQJADE) for contributing this feature!
+
+### Detecting dependent resource API version changes (experimental)
+
+When a dependent resource's CRD gains a new API version and the operator is upgraded to target it,
+comparing the actual resource's `apiVersion` with the desired one detects nothing: the API server
+serves a resource under the requested version regardless of how it is stored, so the comparison
+always trivially matches. `KubernetesDependentResource` consequently ignores `apiVersion` when
+matching.
+
+To still force a one-time update after such an upgrade, `@KubernetesDependent` gained an opt-in
+`detectApiVersionChange` flag:
+
+```java
+@KubernetesDependent(detectApiVersionChange = true)
+public class MyDependentResource extends CRUDKubernetesDependentResource<ConfigMap, MyPrimary> {
+  // ...
+}
+```
+
+When enabled, JOSDK records the API version it applies in the
+`javaoperatorsdk.io/last-applied-api-version` annotation, and the matcher reports a mismatch when
+that marker differs from the version currently in use — which also covers resources predating this
+feature and therefore carrying no marker. After the update the marker matches again, so no
+reconciliation loop results. It is disabled by default, and is not a replacement for Kubernetes'
+[StorageVersionMigration](https://kubernetes.io/docs/tasks/manage-kubernetes-objects/storage-version-migration/),
+which addresses the orthogonal concern of migrating the stored representation.
+
+Thanks to [한의준](https://github.com/hej090224) for this contribution!
+
+## Bug Fixes
+
+### Recently written external resources no longer lost from the cache
+
+An update of the whole resource set of a primary — a poll result or a received event — might have
+been created *before* the reconciler wrote a resource, and therefore not contain it yet. Since such
+updates are treated as the full actual state, the write was lost from the cache, and the next
+reconciliation created a duplicate of an already created resource or repeated an already executed
+update.
+
+Writes are now marked as unconfirmed and retained for the next update if that update either does not
+contain the resource at all (the expected case for a create) or still contains a state that a write
+replaced. Every state replaced since the last update is kept, since the reconciler may write the same
+resource several times in between. Any other state is treated as a change made outside of the
+reconciler and accepted as actual, and marks are dropped on the first update, so a resource really
+deleted or changed meanwhile is not retained indefinitely.
+
+For external state bulk dependent resources that take longer to become visible, the recommended
+approach remains to resolve the actual resources from the state resources in
+`BulkDependentResource.getSecondaryResources` — the state resources are managed by an
+`InformerEventSource` and are therefore always up-to-date regarding the operator's own changes. This
+is now documented and shown in the
+[integration test](https://github.com/operator-framework/java-operator-sdk/tree/main/operator-framework/src/test/java/io/javaoperatorsdk/operator/dependent/externalstate/externalstatebulkdependent).
+
+## Additional Improvements
+
+- **Less redundant work on informer event paths**: `Mappers#fromMetadata` no longer resolves the
+  primary `GroupVersionKind` on every secondary event, `SecondaryToPrimaryFromDefaultAnnotation` no
+  longer builds a whole new mapper per invocation, and `InformerEventSource#start` no longer walks
+  the entire informer cache to seed a primary-to-secondary index that is the no-op implementation
+  (i.e. whenever a `primaryToSecondaryMapper` is configured) — that walk was pure startup latency
+  proportional to the number of cached secondaries.
+- **Informer reuse is logged at `INFO`**, making it visible at a glance which informers a running
+  operator actually shares.
+- **The JavaPoet dependency is gone.** It was only used by the annotation processor to turn a
+  resolved `TypeMirror` into its fully qualified name, which the standard annotation processing API
+  does on its own. JavaPoet has not been released since 2024, which made it a problem for users whose
+  organizations do not approve unmaintained dependencies.
+- Internal clean-ups with no API impact: the Kubernetes resource matchers were simplified, the
+  informer target client is resolved without a downcast, `ResourceState` now owns the
+  trigger-on-all-events flag, and the workflow result map is sized from `Workflow#size`.
+- Additional test coverage, including informer retry after a custom resource deserialization problem,
+  and integration tests for informer sharing, dynamic registration and de-registration against both
+  pool strategies.
+- Dependency updates: Micrometer 1.17.1, JUnit BOM 6.1.3, Jetty 12.1.12, Apache Maven 3.9.16,
+  OpenRewrite 8.90.4 and others.
+
+## Migration Notes
+
+There are **no breaking API changes**; existing code compiles and runs unchanged. Two things are
+worth being aware of:
+
+### Informers are shared by default
+
+This is a behavioral change: event sources with equivalent configuration now share one informer and
+one cache. This should be transparent, but if your operator depends on having a dedicated informer
+per event source, opt out with `withInformerPool(new NonSharingInformerPool())`.
+
+### `InformerEventSource(configuration, context)` is deprecated
+
+Since the informer is now created by the pool from the configuration, the `EventSourceContext` is no
+longer needed to resolve the client. The two-argument constructor is deprecated for removal; drop the
+context argument:
+
+```java
+// before
+new InformerEventSource<>(configuration, context);
+
+// after
+new InformerEventSource<>(configuration);
+```
+
+## Getting Started
+
+```xml
+<dependency>
+    <groupId>io.javaoperatorsdk</groupId>
+    <artifactId>operator-framework</artifactId>
+    <version>5.6.0</version>
+</dependency>
+```
+
+## All Changes
+
+See the [comparison view](https://github.com/operator-framework/java-operator-sdk/compare/v5.5.1...v5.6.0)
+for the full list of changes.
+
+## Feedback
+
+Please report issues or suggest improvements on our
+[GitHub repository](https://github.com/operator-framework/java-operator-sdk/issues).
+
+Happy operator building! 🚀