If more control over the diff behaviour is required, use the CompareOpts or CompareJSONOpts function instead. However, if the webhook is still using the v1.19.x version of the k8s.io/api/core/v1 package that define the Service type, instead of simply ignoring this field, a remove operation will be generated for it. spec.allocateLoadBalancerNodePort in Kubernetes 1.20 to disable allocating a node port for services with Type=LoadBalancer. If your webhook does not have the latest version of the client-go package, or whatever package that contains the types for the resource your manipulating, all fields not known in that version will be deleted.įor example, if your webhook mutate Service resources, a user could set the field. There’s also one other downside to the above example. You can find a detailed description of that problem and its resolution in this GitHub issue. Mutating the original pod object or a copy is up to you, as long as you use the raw bytes of the AdmissionReview object to generate the patch. req is a k8s.io/api/admission/v1.AdmissionRequest object jsondiff. ![]() Comparing between the unmarshaled and copied versions can generate add and change patches below a path not in the original JSON, and the API server will reject your patch.Ī realistic usage would be similar to the following snippet: These will exist when you unmarshal from JSON, because of how Go structs work, but are not in the original JSON. Optional fields being ones that are a struct type, but are not pointers to those structs. ![]() Below is a quote of the original comment: As pointed out by user /u/terinjokes on Reddit, due to the nature of Go structs, the “hydrated” corev1.Pod object may contain “optional fields”, resulting in a patch that state added/changed values that the Kubernetes API server doesn’t know about. Note that the above example is used for simplicity, but in a real-world admission controller, you should create the diff from the raw bytes of the field. The JSON patch can then be used in the response payload of you Kubernetes webhook. Some data types, such as arrays, can be deeply unequal and equivalent at the same time."path ": "/spec/volumes/0/emptyDir/medium " The output is similar to the following: [ Patch, err := jsondiff.Compare(pod, newPod)ī, err := json.MarshalIndent(patch, "", " ") Note that when the Compare or CompareOpts functions are used, the source and target parameters are first marshaled using the encoding/json package in order to obtain their final JSON representation, prior to comparing them. Medium = corev1.StorageMediumDefaultįinally, generate the patch that represents the changes relative to the original value. ![]() Switch storage medium from memory to default. Update the image of the webserver container. Here we modify the image and the storage medium used by the pod's volume shared-data. Secondly, make some changes to the pod spec. Alternatively, if you don't require to keep the original value, you can marshal it to JSON using json.Marshal to store a pre-encoded copy of the document, and mutate the value. The corev1.Pod type defines a DeepCopy method, which is handy, but for other types, a shallow copy is discouraged, instead use a specific library, such as ulule/deepcopier. The first step is to copy the original pod value. Thereby, instead of generating the operations, just copy the source in order to apply the required changes and delegate the patch generation to the library.įor example, given the following corev1.Pod value that represents a Kubernetes demo pod containing a single container: import corev1 "k8s.io/api/core/v1" A concrete application of that would be to generate the patch returned by a Kubernetes dynamic admission controller to mutate a resource. The typical use case within an application is to compare two values of the same type that represents the source and desired target of a JSON document. Example use cases Kubernetes Dynamic Admission Controller :warning: Requires Go1.14+, due to the usage of the package hash/maphash. ![]() Jsondiff is a Go package for computing the diff between two JSON documents as a series of RFC6902 (JSON Patch) operations, which is particularly suitable to create the patch response of a Kubernetes Mutating Webhook for example.įirst, get the latest version of the library using the following command: $ go get /wI2L/
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