feat: client cache for configurable list of gvks#1042
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mblos
marked this pull request as ready for review
July 16, 2026 08:11
mblos
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PhilippMatthes,
auhlig,
juliusclausnitzer,
mblos and
umswmayj
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July 16, 2026 08:11
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Test Coverage ReportTest Coverage 📊: 70.3% |
mblos
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Very nice work :) some first comments (still not completed with reviewing)
| // overlayList merges the overlay entries for the GVK into the informer result, | ||
| // deduplicating by objectKey (overlay wins), dropping tombstones, and filtering | ||
| // overlay-only entries against the list options' label and field selectors. | ||
| func (o *overlay) overlayList(gvk schema.GroupVersionKind, existing []runtime.Object, lo *client.ListOptions) []runtime.Object { |
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If a write changes an indexed field, the inner List filters against the informer (old value), then overlayList silently replaces the object with the new version.
Example: informer has spec.hostName=host-A (RV=5), overlay has spec.hostName=host-B (RV=6). List(MatchingFields{"spec.hostName": "host-A"}) includes the object from the informer, then overlayList swaps in the overlay version.
So you get a host-B object in a host-A query.
Or am I overlooking something?
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| // evictionHandler returns an informer event handler that evicts overlay entries | ||
| // for the GVK when the real object is observed at a >= ResourceVersion. | ||
| func (c *CachingClient) evictionHandler(gvk schema.GroupVersionKind) toolscachek8s.ResourceEventHandler { |
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is DeleteFunc missing here? what if eg someone via kubectl deletes the crd, the informer fires a delete .. but the overlay does not react on it, or?
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| // Delete delegates to the inner client and, on success for a cached GVK, stores | ||
| // a tombstone in the overlay. | ||
| func (c *CachingClient) Delete(ctx context.Context, obj client.Object, opts ...client.DeleteOption) error { |
| } | ||
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| func keyForObject(obj client.Object) objectKey { | ||
| return objectKey{namespace: obj.GetNamespace(), name: obj.GetName()} |
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What if a crd resource has the same name across lh clusters?
PhilippMatthes
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Thank you for incorporating my feedback from #1015 -- especially, the informer-cache idea and reusing metav1.Duration! I've copied over some thoughts and questions and had some new ones along the way. Thanks for considering my feedback.
| hypervisorOvercommitController.Client = multiclusterClient | ||
| if err := hypervisorOvercommitController.SetupWithManager(mgr); err != nil { | ||
| hypervisorOvercommitController.Client = cachingClient | ||
| if err := hypervisorOvercommitController.SetupWithManager(mgr, multiclusterClient); err != nil { |
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Can this cause issues? Inside the SetupWithManager function, aren't there calls that would need to be tunneled by the caching client, such as defining indexes or resource handlers?
Is it possible to wrap it the other way around? Instead of ctrl.Client -> mcl.Client -> clientcache.Client, do ctrl.Client -> clientcache.Client -> mcl.Client? This wouldn't break the pattern here
| clientcache: | ||
| gvks: | ||
| - cortex.cloud/v1alpha1/Reservation | ||
| keystoneSecretRef: |
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Is it expensive to cache resources? If not, why not cache all resources w/o extra configuration?
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| // Inner returns the wrapped client, e.g. for use with a controller Builder that | ||
| // needs the raw client rather than the caching wrapper. | ||
| func (c *CachingClient) Inner() client.Client { return c.Client } |
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CachingClient is not an interface. What purpose does this method have?
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| func (c *CachingClient) Update(ctx context.Context, obj client.Object, opts ...client.UpdateOption) error { | ||
| if err := c.Client.Update(ctx, obj, opts...); err != nil { | ||
| return err | ||
| } | ||
| if gvk, cached := c.gvkFor(obj); cached { | ||
| c.overlay.upsert(gvk, obj) | ||
| } | ||
| return nil | ||
| } |
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What happens when there are two concurrent calls to this function?
Can there be a race condition w.r.t the client update executing in another order than the cache update? Ideally, we should add a globally shared mutex across all CRUD functions so that concurrently reading/writing routines see a consistent state.
| // overlay is the generic, client-independent core of the cache. It stores | ||
| // pending writes keyed by GVK and objectKey and merges them into informer | ||
| // read results until the real object is observed in an informer (eviction). | ||
| type overlay struct { |
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Suggested change
| type overlay struct { | |
| type cache struct { |
| return err | ||
| } | ||
| if gvk, cached := c.gvkFor(obj); cached { | ||
| c.overlay.upsert(gvk, obj) |
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Is it intended that this method call cannot fail when the expected resource has not been created yet? Doesn't this violate the expected controller-runtime client interface protocol?
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| type CachingClient struct { | ||
| client.Client // inner client, used for delegation | ||
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| informers InformerSource | ||
| scheme *runtime.Scheme | ||
| overlay *overlay | ||
| ttl time.Duration | ||
| gvks map[schema.GroupVersionKind]bool | ||
| } |
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I would prefer if we flatten out the caching logic into the client, and not have a separate cache struct.
This would make it easier to understand where the resources stored in the map locally deviate from the resources stored in the controller-runtime client.
For example, the Delete method won't delete the resource from the map immediately -- it will set a deleted flag on the resource. What happens from there, no clue.
| // used for eviction, scheme resolves object GVKs, and conf lists the GVKs to | ||
| // overlay and the TTL. GVK strings are formatted as "<group>/<version>/<Kind>" | ||
| // and are resolved against scheme. | ||
| func New(inner client.Client, informers InformerSource, scheme *runtime.Scheme, conf Config) (*CachingClient, error) { |
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If I see it correctly, you are inputting New(mcl.Client, mcl.Client) into this function in main.go -- what's the purpose of mapping out the InformerSource as an additional interface instead of just taking client.Client?
| return nil, fmt.Errorf("clientcache: object for gvk %s does not implement client.Object", gvk) | ||
| } | ||
| return obj, nil | ||
| } |
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Any specific reason why this code is outside client.go?
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