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Update the DOKS admission controller webhook check 

DOKS has improved handling of webhooks such that the only webhooks that
cause problems are those that:

* Have failurePolicy set to Fail,
* Target a service other than the Kubernetes apiserver, and
* Apply kube-system, and
* Applies to the namespace of the targeted service or are in a
  single-node cluster.

Update the webhook check to reflect this improvement.
image-warning-sha256
Adam Wolfe Gordon 2019-09-09 10:32:11 -06:00
parent d80f88e44e
commit af31dfeada
5 changed files with 339 additions and 152 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

30
checks.md
View File

@ -209,7 +209,10 @@ spec:
- Name: `admission-controller-webhook`
- Groups: `doks`
When you configure admission controllers with webhooks that have a `failurePolicy` set to `Fail`, it prevents managed components like Cilium, kube-proxy, and CoreDNS from starting on a new node during an upgrade. This will result in the cluster upgrade failing.
Admission control webhooks can disrupt upgrade and node replacement operations by preventing system components from starting. Specifically, this happens when an admission control webhook:
* has failurePolicy set to Fail,
* targets a service other than the Kubernetes apiserver, and
* applies to both kube-system and the namespace of the targeted service.
### Example
@ -233,7 +236,7 @@ webhooks:
scope: "Namespaced"
clientConfig:
service:
namespace: kube-system
namespace: webhook
name: webhook-server
path: /pods
admissionReviewVersions:
@ -244,8 +247,23 @@ webhooks:
### How to Fix
There are a few options:
1. Use the `Ignore` `failurePolicy`.
2. Use an apiserver extension as your webhook service.
3. Explicitly exclude the kube-system namespace.
4. Explicitly exclude the webhook service's namespace.
```yaml
# Recommended: Exclude objects in the `kube-system` namespace by explicitly specifying a namespaceSelector or objectSelector
# Recommended: Exclude objects in the `webhook` namespace by explicitly specifying a namespaceSelector.
apiVersion: v1
kind: Namespace
metadata:
name: webhook
labels:
skip-webhooks: "yes"
---
apiVersion: admissionregistration.k8s.io/v1beta1
kind: ValidatingWebhookConfiguration
metadata:
@ -264,7 +282,7 @@ webhooks:
scope: "Namespaced"
clientConfig:
service:
namespace: kube-system
namespace: webhook
name: webhook-server
path: /pods
admissionReviewVersions:
@ -273,8 +291,8 @@ webhooks:
failurePolicy: Fail
namespaceSelector:
matchExpressions:
- key: "doks.digitalocean.com/webhook"
operator: "Exists"
- key: "skip-webhooks"
operator: "DoesNotExist"
```
## Pod State

101
checks/doks/admission_controller_webhook.go
View File

@ -17,10 +17,13 @@ limitations under the License.
package doks
import (
"errors"
"github.com/digitalocean/clusterlint/checks"
"github.com/digitalocean/clusterlint/kube"
ar "k8s.io/api/admissionregistration/v1beta1"
corev1 "k8s.io/api/core/v1"
v1 "k8s.io/api/core/v1"
metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
)
@ -43,46 +46,112 @@ func (w *webhookCheck) Groups() []string {
// Description returns a detailed human-readable description of what this check
// does.
func (w *webhookCheck) Description() string {
return "Check for admission controllers that could prevent managed components from starting"
return "Check for admission control webhooks that could cause problems during upgrades"
}
// Run runs this check on a set of Kubernetes objects. It can return warnings
// (low-priority problems) and errors (high-priority problems) as well as an
// error value indicating that the check failed to run.
// Run runs this check on a set of Kubernetes objects.
func (w *webhookCheck) Run(objects *kube.Objects) ([]checks.Diagnostic, error) {
const apiserverServiceName = "kubernetes"
var diagnostics []checks.Diagnostic
for _, config := range objects.ValidatingWebhookConfigurations.Items {
for _, validatingWebhook := range config.Webhooks {
if *validatingWebhook.FailurePolicy == ar.Fail &&
validatingWebhook.ClientConfig.Service != nil &&
selectorMatchesNamespace(validatingWebhook.NamespaceSelector, objects.SystemNamespace) {
for _, wh := range config.Webhooks {
if *wh.FailurePolicy == ar.Ignore {
// Webhooks with failurePolicy: Ignore are fine.
continue
}
if wh.ClientConfig.Service == nil {
// Webhooks whose targets are external to the cluster are fine.
continue
}
if wh.ClientConfig.Service.Namespace == metav1.NamespaceDefault &&
wh.ClientConfig.Service.Name == apiserverServiceName {
// Webhooks that target the kube-apiserver are fine.
continue
}
if !selectorMatchesNamespace(wh.NamespaceSelector, objects.SystemNamespace) {
// Webhooks that don't apply to kube-system are fine.
continue
}
var svcNamespace *v1.Namespace
for _, ns := range objects.Namespaces.Items {
if ns.Name == wh.ClientConfig.Service.Namespace {
svcNamespace = &ns
}
}
if svcNamespace == nil {
return nil, errors.New("webhook refers to service in non-existent namespace")
}
if !selectorMatchesNamespace(wh.NamespaceSelector, svcNamespace) && len(objects.Nodes.Items) > 1 {
// Webhooks that don't apply to their own namespace are fine, as
// long as there's more than one node in the cluster.
continue
}
d := checks.Diagnostic{
Severity: checks.Error,
Message: "Webhook matches objects in the kube-system namespace. This can cause problems when upgrading the cluster.",
Message: "Validating webhook is configured in such a way that it may be problematic during upgrades.",
Kind: checks.ValidatingWebhookConfiguration,
Object: &config.ObjectMeta,
Owners: config.ObjectMeta.GetOwnerReferences(),
}
diagnostics = append(diagnostics, d)
}
// We don't want to produce diagnostics for multiple webhooks in the
// same webhook configuration, so break out of the inner loop if we
// get here.
break
}
}
for _, config := range objects.MutatingWebhookConfigurations.Items {
for _, mutatingWebhook := range config.Webhooks {
if *mutatingWebhook.FailurePolicy == ar.Fail &&
mutatingWebhook.ClientConfig.Service != nil &&
selectorMatchesNamespace(mutatingWebhook.NamespaceSelector, objects.SystemNamespace) {
for _, wh := range config.Webhooks {
if *wh.FailurePolicy == ar.Ignore {
// Webhooks with failurePolicy: Ignore are fine.
continue
}
if wh.ClientConfig.Service == nil {
// Webhooks whose targets are external to the cluster are fine.
continue
}
if wh.ClientConfig.Service.Namespace == metav1.NamespaceDefault &&
wh.ClientConfig.Service.Name == apiserverServiceName {
// Webhooks that target the kube-apiserver are fine.
continue
}
if !selectorMatchesNamespace(wh.NamespaceSelector, objects.SystemNamespace) {
// Webhooks that don't apply to kube-system are fine.
continue
}
var svcNamespace *v1.Namespace
for _, ns := range objects.Namespaces.Items {
if ns.Name == wh.ClientConfig.Service.Namespace {
svcNamespace = &ns
}
}
if svcNamespace == nil {
return nil, errors.New("webhook refers to service in non-existent namespace")
}
if !selectorMatchesNamespace(wh.NamespaceSelector, svcNamespace) && len(objects.Nodes.Items) > 1 {
// Webhooks that don't apply to their own namespace are fine, as
// long as there's more than one node in the cluster.
continue
}
d := checks.Diagnostic{
Severity: checks.Error,
Message: "Webhook matches objects in the kube-system namespace. This can cause problems when upgrading the cluster.",
Message: "Mutating webhook is configured in such a way that it may be problematic during upgrades.",
Kind: checks.MutatingWebhookConfiguration,
Object: &config.ObjectMeta,
Owners: config.ObjectMeta.GetOwnerReferences(),
}
diagnostics = append(diagnostics, d)
}
// We don't want to produce diagnostics for multiple webhooks in the
// same webhook configuration, so break out of the inner loop if we
// get here.
break
}
}
return diagnostics, nil

297
checks/doks/admission_controller_webhook_test.go
View File

@ -27,6 +27,8 @@ import (
metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
)
var webhookURL = "https://example.com/webhook"
func TestWebhookCheckMeta(t *testing.T) {
webhookCheck := webhookCheck{}
assert.Equal(t, "admission-controller-webhook", webhookCheck.Name())
@ -58,69 +60,180 @@ func TestWebhookError(t *testing.T) {
},
{
name: "failure policy is ignore",
objs: initObjects(ar.Ignore),
objs: webhookTestObjects(
ar.Ignore,
&metav1.LabelSelector{},
ar.WebhookClientConfig{
Service: &ar.ServiceReference{
Namespace: "webhook",
Name: "webhook-service",
},
},
2,
),
expected: nil,
},
{
name: "webook does not use service",
objs: webhookURL(),
objs: webhookTestObjects(
ar.Fail,
&metav1.LabelSelector{},
ar.WebhookClientConfig{
URL: &webhookURL,
},
2,
),
expected: nil,
},
{
name: "namespace selector is empty",
objs: initObjects(ar.Fail),
expected: webhookErrors(),
name: "webook service is apiserver",
objs: webhookTestObjects(
ar.Fail,
&metav1.LabelSelector{},
ar.WebhookClientConfig{
Service: &ar.ServiceReference{
Namespace: "default",
Name: "kubernetes",
},
{
name: "namespace selector matches label",
objs: label(map[string]string{"doks_key": "bar"}),
expected: webhookErrors(),
},
{
name: "namespace selector does not match label",
objs: label(map[string]string{"non-existent-label-on-namespace": "bar"}),
2,
),
expected: nil,
},
{
name: "namespace selector matches OpExists expression",
objs: expr("doks_key", []string{}, metav1.LabelSelectorOpExists),
expected: webhookErrors(),
name: "namespace label selector does not match kube-system",
objs: webhookTestObjects(
ar.Fail,
&metav1.LabelSelector{
MatchLabels: map[string]string{"non-existent-label-on-namespace": "bar"},
},
{
name: "namespace selector matches OpDoesNotExist expression",
objs: expr("random", []string{}, metav1.LabelSelectorOpDoesNotExist),
expected: webhookErrors(),
ar.WebhookClientConfig{
Service: &ar.ServiceReference{
Namespace: "webhook",
Name: "webhook-service",
},
{
name: "namespace selector matches OpIn expression",
objs: expr("doks_key", []string{"bar"}, metav1.LabelSelectorOpIn),
expected: webhookErrors(),
},
{
name: "namespace selector matches OpNotIn expression",
objs: expr("doks_key", []string{"non-existent"}, metav1.LabelSelectorOpNotIn),
expected: webhookErrors(),
},
{
name: "namespace selector does not match OpExists expression",
objs: expr("non-existent", []string{}, metav1.LabelSelectorOpExists),
2,
),
expected: nil,
},
{
name: "namespace selector does not match OpDoesNotExist expression",
objs: expr("doks_key", []string{}, metav1.LabelSelectorOpDoesNotExist),
name: "namespace OpExists expression selector does not match kube-system",
objs: webhookTestObjects(
ar.Fail,
&metav1.LabelSelector{
MatchExpressions: expr("non-existent", []string{}, metav1.LabelSelectorOpExists),
},
ar.WebhookClientConfig{
Service: &ar.ServiceReference{
Namespace: "webhook",
Name: "webhook-service",
},
},
2,
),
expected: nil,
},
{
name: "namespace selector does not match OpIn expression",
objs: expr("doks_key", []string{"non-existent"}, metav1.LabelSelectorOpIn),
name: "namespace OpDoesNotExist expression selector does not match kube-system",
objs: webhookTestObjects(
ar.Fail,
&metav1.LabelSelector{
MatchExpressions: expr("doks_key", []string{}, metav1.LabelSelectorOpDoesNotExist),
},
ar.WebhookClientConfig{
Service: &ar.ServiceReference{
Namespace: "webhook",
Name: "webhook-service",
},
},
2,
),
expected: nil,
},
{
name: "namespace selector does not match OpNotIn expression",
objs: expr("doks_key", []string{"bar"}, metav1.LabelSelectorOpNotIn),
name: "namespace OpIn expression selector does not match kube-system",
objs: webhookTestObjects(
ar.Fail,
&metav1.LabelSelector{
MatchExpressions: expr("doks_key", []string{"non-existent"}, metav1.LabelSelectorOpIn),
},
ar.WebhookClientConfig{
Service: &ar.ServiceReference{
Namespace: "webhook",
Name: "webhook-service",
},
},
2,
),
expected: nil,
},
{
name: "namespace OpNotIn expression selector does not match kube-system",
objs: webhookTestObjects(
ar.Fail,
&metav1.LabelSelector{
MatchExpressions: expr("doks_key", []string{"bar"}, metav1.LabelSelectorOpNotIn),
},
ar.WebhookClientConfig{
Service: &ar.ServiceReference{
Namespace: "webhook",
Name: "webhook-service",
},
},
2,
),
expected: nil,
},
{
name: "namespace label selector does not match own namespace",
objs: webhookTestObjects(
ar.Fail,
&metav1.LabelSelector{
MatchLabels: map[string]string{"doks_key": "bar"},
},
ar.WebhookClientConfig{
Service: &ar.ServiceReference{
Namespace: "webhook",
Name: "webhook-service",
},
},
2,
),
expected: nil,
},
{
name: "single-node cluster",
objs: webhookTestObjects(
ar.Fail,
&metav1.LabelSelector{
MatchLabels: map[string]string{"doks_key": "bar"},
},
ar.WebhookClientConfig{
Service: &ar.ServiceReference{
Namespace: "webhook",
Name: "webhook-service",
},
},
1,
),
expected: webhookErrors(),
},
{
name: "webhook applies to its own namespace and kube-system",
objs: webhookTestObjects(
ar.Fail,
&metav1.LabelSelector{},
ar.WebhookClientConfig{
Service: &ar.ServiceReference{
Namespace: "webhook",
Name: "webhook-service",
},
},
2,
),
expected: webhookErrors(),
},
}
webhookCheck := webhookCheck{}
@ -134,13 +247,45 @@ func TestWebhookError(t *testing.T) {
}
}
func initObjects(failurePolicyType ar.FailurePolicyType) *kube.Objects {
func expr(key string, values []string, op metav1.LabelSelectorOperator) []metav1.LabelSelectorRequirement {
return []metav1.LabelSelectorRequirement{{
Key: key,
Operator: op,
Values: values,
}}
}
func webhookTestObjects(
failurePolicyType ar.FailurePolicyType,
nsSelector *metav1.LabelSelector,
clientConfig ar.WebhookClientConfig,
numNodes int,
) *kube.Objects {
objs := &kube.Objects{
SystemNamespace: &corev1.Namespace{
TypeMeta: metav1.TypeMeta{Kind: "Namespace", APIVersion: "v1"},
ObjectMeta: metav1.ObjectMeta{
Name: "kube-system",
Labels: map[string]string{"doks_key": "bar"}},
Labels: map[string]string{"doks_key": "bar"},
},
},
Namespaces: &corev1.NamespaceList{
Items: []corev1.Namespace{
{
TypeMeta: metav1.TypeMeta{Kind: "Namespace", APIVersion: "v1"},
ObjectMeta: metav1.ObjectMeta{
Name: "kube-system",
Labels: map[string]string{"doks_key": "bar"},
},
},
{
TypeMeta: metav1.TypeMeta{Kind: "Namespace", APIVersion: "v1"},
ObjectMeta: metav1.ObjectMeta{
Name: "webhook",
Labels: map[string]string{"doks_key": "xyzzy"},
},
},
},
},
MutatingWebhookConfigurations: &ar.MutatingWebhookConfigurationList{
Items: []ar.MutatingWebhookConfiguration{
@ -153,13 +298,8 @@ func initObjects(failurePolicyType ar.FailurePolicyType) *kube.Objects {
{
Name: "mw_foo",
FailurePolicy: &failurePolicyType,
NamespaceSelector: &metav1.LabelSelector{},
ClientConfig: ar.WebhookClientConfig{
Service: &ar.ServiceReference{
Name: "some-svc",
Namespace: "k8s",
},
},
NamespaceSelector: nsSelector,
ClientConfig: clientConfig,
},
},
},
@ -176,83 +316,38 @@ func initObjects(failurePolicyType ar.FailurePolicyType) *kube.Objects {
{
Name: "vw_foo",
FailurePolicy: &failurePolicyType,
NamespaceSelector: &metav1.LabelSelector{},
ClientConfig: ar.WebhookClientConfig{
Service: &ar.ServiceReference{
Name: "some-svc",
Namespace: "k8s",
NamespaceSelector: nsSelector,
ClientConfig: clientConfig,
},
},
},
},
},
},
},
}
return objs
}
func webhookURL() *kube.Objects {
var url = "https://example.com/webhook/action"
objs := initObjects(ar.Fail)
objs.ValidatingWebhookConfigurations.Items[0].Webhooks[0].ClientConfig = ar.WebhookClientConfig{
URL: &url,
}
objs.MutatingWebhookConfigurations.Items[0].Webhooks[0].ClientConfig = ar.WebhookClientConfig{
URL: &url,
}
return objs
}
func label(label map[string]string) *kube.Objects {
objs := initObjects(ar.Fail)
objs.ValidatingWebhookConfigurations.Items[0].Webhooks[0].NamespaceSelector = &metav1.LabelSelector{
MatchLabels: label,
}
objs.MutatingWebhookConfigurations.Items[0].Webhooks[0].NamespaceSelector = &metav1.LabelSelector{
MatchLabels: label,
}
return objs
}
func expr(key string, values []string, labelOperator metav1.LabelSelectorOperator) *kube.Objects {
objs := initObjects(ar.Fail)
objs.ValidatingWebhookConfigurations.Items[0].Webhooks[0].NamespaceSelector = &metav1.LabelSelector{
MatchExpressions: []metav1.LabelSelectorRequirement{
{
Key: key,
Operator: labelOperator,
Values: values,
},
},
}
objs.MutatingWebhookConfigurations.Items[0].Webhooks[0].NamespaceSelector = &metav1.LabelSelector{
MatchExpressions: []metav1.LabelSelectorRequirement{
{
Key: key,
Operator: labelOperator,
Values: values,
},
},
objs.Nodes = &corev1.NodeList{}
for i := 0; i < numNodes; i++ {
objs.Nodes.Items = append(objs.Nodes.Items, corev1.Node{})
}
return objs
}
func webhookErrors() []checks.Diagnostic {
objs := initObjects(ar.Fail)
objs := webhookTestObjects(ar.Fail, nil, ar.WebhookClientConfig{}, 0)
validatingConfig := objs.ValidatingWebhookConfigurations.Items[0]
mutatingConfig := objs.MutatingWebhookConfigurations.Items[0]
diagnostics := []checks.Diagnostic{
{
Severity: checks.Error,
Message: "Webhook matches objects in the kube-system namespace. This can cause problems when upgrading the cluster.",
Message: "Validating webhook is configured in such a way that it may be problematic during upgrades.",
Kind: checks.ValidatingWebhookConfiguration,
Object: &validatingConfig.ObjectMeta,
Owners: validatingConfig.ObjectMeta.GetOwnerReferences(),
},
{
Severity: checks.Error,
Message: "Webhook matches objects in the kube-system namespace. This can cause problems when upgrading the cluster.",
Message: "Mutating webhook is configured in such a way that it may be problematic during upgrades.",
Kind: checks.MutatingWebhookConfiguration,
Object: &mutatingConfig.ObjectMeta,
Owners: mutatingConfig.ObjectMeta.GetOwnerReferences(),

4
checks/doks/node_name_pod_selector_test.go
View File

@ -56,7 +56,7 @@ func TestNodeNameError(t *testing.T) {
{
name: "node name used in node selector",
objs: invalidPod(),
expected: warnings(invalidPod(), podSelectorCheck.Name()),
expected: expectedWarnings(invalidPod(), podSelectorCheck.Name()),
},
}
@ -89,7 +89,7 @@ func invalidPod() *kube.Objects {
return objs
}
func warnings(objs *kube.Objects, name string) []checks.Diagnostic {
func expectedWarnings(objs *kube.Objects, name string) []checks.Diagnostic {
pod := objs.Pods.Items[0]
diagnostics := []checks.Diagnostic{
{

5
kube/objects.go
View File

@ -54,6 +54,7 @@ type Objects struct {
LimitRanges *corev1.LimitRangeList
MutatingWebhookConfigurations *ar.MutatingWebhookConfigurationList
ValidatingWebhookConfigurations *ar.ValidatingWebhookConfigurationList
Namespaces *corev1.NamespaceList
}
// Client encapsulates a client for a Kubernetes cluster.
@ -131,6 +132,10 @@ func (c *Client) FetchObjects(ctx context.Context) (*Objects, error) {
objects.ValidatingWebhookConfigurations, err = admissionControllerClient.ValidatingWebhookConfigurations().List(opts)
return
})
g.Go(func() (err error) {
objects.Namespaces, err = client.Namespaces().List(opts)
return
})
err := g.Wait()
if err != nil {