Chapter 4. MutatingWebhookConfiguration [admissionregistration.k8s.io/v1]

admissionReviewVersions

array (string)

AdmissionReviewVersions is an ordered list of preferred AdmissionReview versions the Webhook expects. API server will try to use first version in the list which it supports. If none of the versions specified in this list supported by API server, validation will fail for this object. If a persisted webhook configuration specifies allowed versions and does not include any versions known to the API Server, calls to the webhook will fail and be subject to the failure policy.

clientConfig

object

WebhookClientConfig contains the information to make a TLS connection with the webhook

failurePolicy

string

FailurePolicy defines how unrecognized errors from the admission endpoint are handled - allowed values are Ignore or Fail. Defaults to Fail.

Possible enum values: - "Fail" means that an error calling the webhook causes the admission to fail. - "Ignore" means that an error calling the webhook is ignored.

matchConditions

array

MatchConditions is a list of conditions that must be met for a request to be sent to this webhook. Match conditions filter requests that have already been matched by the rules, namespaceSelector, and objectSelector. An empty list of matchConditions matches all requests. There are a maximum of 64 match conditions allowed.

The exact matching logic is (in order): 1. If ANY matchCondition evaluates to FALSE, the webhook is skipped. 2. If ALL matchConditions evaluate to TRUE, the webhook is called. 3. If any matchCondition evaluates to an error (but none are FALSE): - If failurePolicy=Fail, reject the request - If failurePolicy=Ignore, the error is ignored and the webhook is skipped

This is a beta feature and managed by the AdmissionWebhookMatchConditions feature gate.

matchConditions[]

object

MatchCondition represents a condition which must by fulfilled for a request to be sent to a webhook.

matchPolicy

string

matchPolicy defines how the "rules" list is used to match incoming requests. Allowed values are "Exact" or "Equivalent".

- Exact: match a request only if it exactly matches a specified rule. For example, if deployments can be modified via apps/v1, apps/v1beta1, and extensions/v1beta1, but "rules" only included apiGroups:["apps"], apiVersions:["v1"], resources: ["deployments"], a request to apps/v1beta1 or extensions/v1beta1 would not be sent to the webhook.

- Equivalent: match a request if modifies a resource listed in rules, even via another API group or version. For example, if deployments can be modified via apps/v1, apps/v1beta1, and extensions/v1beta1, and "rules" only included apiGroups:["apps"], apiVersions:["v1"], resources: ["deployments"], a request to apps/v1beta1 or extensions/v1beta1 would be converted to apps/v1 and sent to the webhook.

Defaults to "Equivalent"

Possible enum values: - "Equivalent" means requests should be sent to the webhook if they modify a resource listed in rules via another API group or version. - "Exact" means requests should only be sent to the webhook if they exactly match a given rule.

name

string

The name of the admission webhook. Name should be fully qualified, e.g., imagepolicy.kubernetes.io, where "imagepolicy" is the name of the webhook, and kubernetes.io is the name of the organization. Required.

namespaceSelector

LabelSelector

NamespaceSelector decides whether to run the webhook on an object based on whether the namespace for that object matches the selector. If the object itself is a namespace, the matching is performed on object.metadata.labels. If the object is another cluster scoped resource, it never skips the webhook.

For example, to run the webhook on any objects whose namespace is not associated with "runlevel" of "0" or "1"; you will set the selector as follows: "namespaceSelector": { "matchExpressions": [ { "key": "runlevel", "operator": "NotIn", "values": [ "0", "1" ] } ] }

If instead you want to only run the webhook on any objects whose namespace is associated with the "environment" of "prod" or "staging"; you will set the selector as follows: "namespaceSelector": { "matchExpressions": [ { "key": "environment", "operator": "In", "values": [ "prod", "staging" ] } ] }

See https://kubernetes.io/docs/concepts/overview/working-with-objects/labels/ for more examples of label selectors.

Default to the empty LabelSelector, which matches everything.

objectSelector

LabelSelector

ObjectSelector decides whether to run the webhook based on if the object has matching labels. objectSelector is evaluated against both the oldObject and newObject that would be sent to the webhook, and is considered to match if either object matches the selector. A null object (oldObject in the case of create, or newObject in the case of delete) or an object that cannot have labels (like a DeploymentRollback or a PodProxyOptions object) is not considered to match. Use the object selector only if the webhook is opt-in, because end users may skip the admission webhook by setting the labels. Default to the empty LabelSelector, which matches everything.

reinvocationPolicy

string

reinvocationPolicy indicates whether this webhook should be called multiple times as part of a single admission evaluation. Allowed values are "Never" and "IfNeeded".

Never: the webhook will not be called more than once in a single admission evaluation.

IfNeeded: the webhook will be called at least one additional time as part of the admission evaluation if the object being admitted is modified by other admission plugins after the initial webhook call. Webhooks that specify this option must be idempotent, able to process objects they previously admitted. Note: * the number of additional invocations is not guaranteed to be exactly one. * if additional invocations result in further modifications to the object, webhooks are not guaranteed to be invoked again. * webhooks that use this option may be reordered to minimize the number of additional invocations. * to validate an object after all mutations are guaranteed complete, use a validating admission webhook instead.

Defaults to "Never".

Possible enum values: - "IfNeeded" indicates that the webhook may be called at least one additional time as part of the admission evaluation if the object being admitted is modified by other admission plugins after the initial webhook call. - "Never" indicates that the webhook must not be called more than once in a single admission evaluation.

rules

array

Rules describes what operations on what resources/subresources the webhook cares about. The webhook cares about an operation if it matches any Rule. However, in order to prevent ValidatingAdmissionWebhooks and MutatingAdmissionWebhooks from putting the cluster in a state which cannot be recovered from without completely disabling the plugin, ValidatingAdmissionWebhooks and MutatingAdmissionWebhooks are never called on admission requests for ValidatingWebhookConfiguration and MutatingWebhookConfiguration objects.

rules[]

object

RuleWithOperations is a tuple of Operations and Resources. It is recommended to make sure that all the tuple expansions are valid.

sideEffects

string

SideEffects states whether this webhook has side effects. Acceptable values are: None, NoneOnDryRun (webhooks created via v1beta1 may also specify Some or Unknown). Webhooks with side effects MUST implement a reconciliation system, since a request may be rejected by a future step in the admission chain and the side effects therefore need to be undone. Requests with the dryRun attribute will be auto-rejected if they match a webhook with sideEffects == Unknown or Some.

Possible enum values: - "None" means that calling the webhook will have no side effects. - "NoneOnDryRun" means that calling the webhook will possibly have side effects, but if the request being reviewed has the dry-run attribute, the side effects will be suppressed. - "Some" means that calling the webhook will possibly have side effects. If a request with the dry-run attribute would trigger a call to this webhook, the request will instead fail. - "Unknown" means that no information is known about the side effects of calling the webhook. If a request with the dry-run attribute would trigger a call to this webhook, the request will instead fail.

timeoutSeconds

integer

TimeoutSeconds specifies the timeout for this webhook. After the timeout passes, the webhook call will be ignored or the API call will fail based on the failure policy. The timeout value must be between 1 and 30 seconds. Default to 10 seconds.

caBundle

string

caBundle is a PEM encoded CA bundle which will be used to validate the webhook’s server certificate. If unspecified, system trust roots on the apiserver are used.

service

object

ServiceReference holds a reference to Service.legacy.k8s.io

url

string

url gives the location of the webhook, in standard URL form (scheme://host:port/path). Exactly one of url or service must be specified.

The host should not refer to a service running in the cluster; use the service field instead. The host might be resolved via external DNS in some apiservers (e.g., kube-apiserver cannot resolve in-cluster DNS as that would be a layering violation). host may also be an IP address.

Please note that using localhost or 127.0.0.1 as a host is risky unless you take great care to run this webhook on all hosts which run an apiserver which might need to make calls to this webhook. Such installs are likely to be non-portable, i.e., not easy to turn up in a new cluster.

The scheme must be "https"; the URL must begin with "https://".

A path is optional, and if present may be any string permissible in a URL. You may use the path to pass an arbitrary string to the webhook, for example, a cluster identifier.

Attempting to use a user or basic auth e.g. "user:password@" is not allowed. Fragments ("#…​") and query parameters ("?…​") are not allowed, either.

name

string

name is the name of the service. Required

namespace

string

namespace is the namespace of the service. Required

path

string

path is an optional URL path which will be sent in any request to this service.

port

integer

If specified, the port on the service that hosting webhook. Default to 443 for backward compatibility. port should be a valid port number (1-65535, inclusive).

expression

string

Expression represents the expression which will be evaluated by CEL. Must evaluate to bool. CEL expressions have access to the contents of the AdmissionRequest and Authorizer, organized into CEL variables:

'object' - The object from the incoming request. The value is null for DELETE requests. 'oldObject' - The existing object. The value is null for CREATE requests. 'request' - Attributes of the admission request(/pkg/apis/admission/types.go#AdmissionRequest). 'authorizer' - A CEL Authorizer. May be used to perform authorization checks for the principal (user or service account) of the request. See https://pkg.go.dev/k8s.io/apiserver/pkg/cel/library#Authz 'authorizer.requestResource' - A CEL ResourceCheck constructed from the 'authorizer' and configured with the request resource. Documentation on CEL: https://kubernetes.io/docs/reference/using-api/cel/

Required.

name

string

Name is an identifier for this match condition, used for strategic merging of MatchConditions, as well as providing an identifier for logging purposes. A good name should be descriptive of the associated expression. Name must be a qualified name consisting of alphanumeric characters, '-', '' or '.', and must start and end with an alphanumeric character (e.g. 'MyName', or 'my.name', or '123-abc', regex used for validation is '([A-Za-z0-9][-A-Za-z0-9.]*)?[A-Za-z0-9]') with an optional DNS subdomain prefix and '/' (e.g. 'example.com/MyName')

Required.

apiGroups

array (string)

APIGroups is the API groups the resources belong to. '' is all groups. If '' is present, the length of the slice must be one. Required.

apiVersions

array (string)

APIVersions is the API versions the resources belong to. '' is all versions. If '' is present, the length of the slice must be one. Required.

operations

array (string)

Operations is the operations the admission hook cares about - CREATE, UPDATE, DELETE, CONNECT or * for all of those operations and any future admission operations that are added. If '*' is present, the length of the slice must be one. Required.

resources

array (string)

Resources is a list of resources this rule applies to.

For example: 'pods' means pods. 'pods/log' means the log subresource of pods. '' means all resources, but not subresources. 'pods/' means all subresources of pods. '/scale' means all scale subresources. '/*' means all resources and their subresources.

If wildcard is present, the validation rule will ensure resources do not overlap with each other.

Depending on the enclosing object, subresources might not be allowed. Required.

scope

string

scope specifies the scope of this rule. Valid values are "Cluster", "Namespaced", and "" "Cluster" means that only cluster-scoped resources will match this rule. Namespace API objects are cluster-scoped. "Namespaced" means that only namespaced resources will match this rule. "" means that there are no scope restrictions. Subresources match the scope of their parent resource. Default is "*".

dryRun

string

When present, indicates that modifications should not be persisted. An invalid or unrecognized dryRun directive will result in an error response and no further processing of the request. Valid values are: - All: all dry run stages will be processed

200 - OK

Status schema

401 - Unauthorized

Empty

200 - OK

MutatingWebhookConfigurationList schema

401 - Unauthorized

Empty

dryRun

string

When present, indicates that modifications should not be persisted. An invalid or unrecognized dryRun directive will result in an error response and no further processing of the request. Valid values are: - All: all dry run stages will be processed

fieldValidation

string

fieldValidation instructs the server on how to handle objects in the request (POST/PUT/PATCH) containing unknown or duplicate fields. Valid values are: - Ignore: This will ignore any unknown fields that are silently dropped from the object, and will ignore all but the last duplicate field that the decoder encounters. This is the default behavior prior to v1.23. - Warn: This will send a warning via the standard warning response header for each unknown field that is dropped from the object, and for each duplicate field that is encountered. The request will still succeed if there are no other errors, and will only persist the last of any duplicate fields. This is the default in v1.23+ - Strict: This will fail the request with a BadRequest error if any unknown fields would be dropped from the object, or if any duplicate fields are present. The error returned from the server will contain all unknown and duplicate fields encountered.

body

MutatingWebhookConfiguration schema

200 - OK

MutatingWebhookConfiguration schema

201 - Created

MutatingWebhookConfiguration schema

202 - Accepted

MutatingWebhookConfiguration schema

401 - Unauthorized

Empty

200 - OK

WatchEvent schema

401 - Unauthorized

Empty

name

string

name of the MutatingWebhookConfiguration

dryRun

string

When present, indicates that modifications should not be persisted. An invalid or unrecognized dryRun directive will result in an error response and no further processing of the request. Valid values are: - All: all dry run stages will be processed

200 - OK

Status schema

202 - Accepted

Status schema

401 - Unauthorized

Empty

200 - OK

MutatingWebhookConfiguration schema

401 - Unauthorized

Empty

dryRun

string

When present, indicates that modifications should not be persisted. An invalid or unrecognized dryRun directive will result in an error response and no further processing of the request. Valid values are: - All: all dry run stages will be processed

fieldValidation

string

fieldValidation instructs the server on how to handle objects in the request (POST/PUT/PATCH) containing unknown or duplicate fields. Valid values are: - Ignore: This will ignore any unknown fields that are silently dropped from the object, and will ignore all but the last duplicate field that the decoder encounters. This is the default behavior prior to v1.23. - Warn: This will send a warning via the standard warning response header for each unknown field that is dropped from the object, and for each duplicate field that is encountered. The request will still succeed if there are no other errors, and will only persist the last of any duplicate fields. This is the default in v1.23+ - Strict: This will fail the request with a BadRequest error if any unknown fields would be dropped from the object, or if any duplicate fields are present. The error returned from the server will contain all unknown and duplicate fields encountered.

200 - OK

MutatingWebhookConfiguration schema

201 - Created

MutatingWebhookConfiguration schema

401 - Unauthorized

Empty

dryRun

string

When present, indicates that modifications should not be persisted. An invalid or unrecognized dryRun directive will result in an error response and no further processing of the request. Valid values are: - All: all dry run stages will be processed

fieldValidation

string

fieldValidation instructs the server on how to handle objects in the request (POST/PUT/PATCH) containing unknown or duplicate fields. Valid values are: - Ignore: This will ignore any unknown fields that are silently dropped from the object, and will ignore all but the last duplicate field that the decoder encounters. This is the default behavior prior to v1.23. - Warn: This will send a warning via the standard warning response header for each unknown field that is dropped from the object, and for each duplicate field that is encountered. The request will still succeed if there are no other errors, and will only persist the last of any duplicate fields. This is the default in v1.23+ - Strict: This will fail the request with a BadRequest error if any unknown fields would be dropped from the object, or if any duplicate fields are present. The error returned from the server will contain all unknown and duplicate fields encountered.

body

MutatingWebhookConfiguration schema

200 - OK

MutatingWebhookConfiguration schema

201 - Created

MutatingWebhookConfiguration schema

401 - Unauthorized

Empty

name

string

name of the MutatingWebhookConfiguration

200 - OK

WatchEvent schema

401 - Unauthorized

Empty