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HNC: How-to

[UPDATE MAY 2021]: HNC has graduated to its own repo! Please visit that repo for the latest version of this user guide.

Part of the HNC User Guide

This document describes common tasks you might want to accomplish using HNC.

Table of contents

Use hierarchical namespaces

Prepare to use hierarchical namespaces as a user

It is possible to interact with hierarchical namespaces purely through Kubernetes tools such as kubectl. However, the kubectl-hns plugin greatly simplifies several tasks. This guide illustrates both methods, but we recommend installing the kubectl-hns plugin.

You can install the plugin by following the instructions for the latest release.

Create a subnamespace

In order to create a subnamespace of another namespace, you must have permissions to create the subnamespaceanchor.hnc.x-k8s.io resource in that namespace. Ask your cluster administrator to give you this permission if you do not have it.

To create a subnamespace “child” underneath parent “parent” using the kubectl plugin:

$ kubectl hns create child -n parent

This creates an object called a subnamespace anchor in the parent namespace. HNC detects that this anchor has been added, and creates the subnamespace for you.

To verify that this worked:

$ kubectl hns tree parent
# Output:
parent
└── child

To create a subnamespace without the plugin, create the following resource:

$ kubectl apply -f - <<EOF
apiVersion: hnc.x-k8s.io/v1alpha2
kind: SubnamespaceAnchor
metadata:
  namespace: parent
  name: child
EOF

To verify that this has worked (see comments):

$ kubectl get ns child
# Output:
NAME   STATUS   AGE
child  Active   1m

$ kubectl get -oyaml -nparent subns child
# Output:
apiVersion: hnc.x-k8s.io/v1alpha2
kind: SubnamespaceAnchor
metadata:
  name: child
  namespace: default
  … < other stuff > …
status:
  status: ok # <--- This will be something other than 'ok' if there's a problem

You can also look inside the new namespace to confirm its set up correctly:

$ kubectl get -oyaml -nchild hierarchyconfiguration hierarchy
# Output:
apiVersion: hnc.x-k8s.io/v1alpha2
kind: HierarchyConfiguration
metadata:
  name: hierarchy
  namespace: child
  … < other stuff > …
spec:
  parent: default # <--- this should be the namespace of the anchor
status: {}

Inspect namespace hierarchies

To get an overview of the hierarchy of your entire cluster, use one of the following variants of the tree command:

kubectl hns tree --all-namespaces
kubectl hns tree -A

You can also limit this display to a single subtree via:

kubectl hns tree ROOT_NAMESPACE

In addition to showing you the structure of your hierarchy, it will also give you high-level information on any problems with the hierarchies, known as conditions.

For detailed information on any one namespace, including:

  • Its children
  • Its conditions
  • Any HNC problems with objects in the namespace

Use the more detailed describe command:

kubectl hns describe NAMESPACE

Propagating policies across namespaces

By default, HNC propagates RBAC Role and RoleBinding objects. If you create objects of these kinds in a parent namespace, it will automatically be copied into any descendant namespaces as well. You cannot modify these propagated copies; HNC’s admission controllers will attempt to stop you from editing them.

Similarly, if you try to create an object in a parent ancestor with the same name as an object in one of its descendants, HNC will stop you from doing so, because this would result in the objects in the descendants being silently overwritten. HNC will also prevent you from changing the parent of a namespace if this would result in objects being overwritten.

However, if you bypass these admission controllers - for example, by updating objects while HNC is being upgraded - HNC will overwrite conflicting objects in descendant namespaces. This is to ensure that if you are able to successfully create a policy in an ancestor namespace, you can be confident that it will be uniformly applied to all descendant namespaces.

HNC can also propagate objects other than RBAC objects, but only cluster administrators can modify this. See here for instructions.

Occasionally, objects might fail to be propagated to descendant namespaces for a variety of reasons - e.g., HNC itself might not have sufficient RBAC permissions. To understand why an object is not being propagated to a namespace, use kubectl hns describe <ns>, where <ns> is either the source (ancestor) or destination (descendant) namespace.

Select namespaces based on their hierarchies

HNC inserts labels onto your namespaces to allow trees (and subtrees) of namespaces to be selected by policies such as NetworkPolicy.

This section is under construction (as of Oct 2020). For now, please see the quickstart.

Delete a subnamespace

In order to delete a subnamespace, you must first have permissions to delete its anchor in its parent namespace. Ask your cluster administrator to give you this permission if you do not have it.

Subnamespaces are always manipulated via their anchors. For example, you cannot delete a subnamespace by deleting it directly:

$ kubectl delete namespace child
# Output:
Error from server (Forbidden): admission webhook "namespaces.x-hnc.k8s.io" denied the request: The namespace "child" is a subnamespace. Please delete the subnamespace anchor from the parent namespace "parent" instead.

Instead, you must delete its anchor (note that subns is a short form of subnamespaceanchor):

$ kubectl delete subns child -n parent

This seems to imply that if you delete a parent namespace, all its subnamespace children (and their descendants) will be deleted as well, since all objects in a namespace (such as anchors) are deleted along with the namespace. However, if you actually try this, you'll get an error:

$ kubectl delete namespace parent
# Output:
Error from server (Forbidden): admission webhook "namespaces.hnc.x-k8s.io" denied the request: Please set allowCascadingDeletion first either in the parent namespace or in all the subnamespaces.
 Subnamespace(s) without allowCascadingDeletion set: [child].

These errors are there for your protection. Deleting namespaces is very dangerous, and deleting subnamespaces can result in entire subtrees of namespaces being deleted as well. Therefore, if deleting a namespace (or subnamespace) would result in the deletion of any namespace other than the one explicitly being deleted, HNC requires that you must specify the allowCascadingDeletion field on either all the namespaces that will be implicitly deleted, or any of their ancestors.

The allowCascadingDeletion field is a bit like rm -rf in a Linux shell.

WARNING: this option is very dangerous, so you should only set it on the lowest possible level of the hierarchy.

WARNING: any subnamespaces of the namespace you are deleting will also be deleted, and so will any subnamespaces of those namespaces, and so on. However, any full namespaces that are descendants of a subnamespace will not be deleted.

To set the allowCascadingDeletion field on a namespace using the plugin:

$ kubectl hns set parent --allowCascadingDeletion
# Output:
Allowing cascading deletion on 'parent'
Succesfully updated 1 property of the hierarchical configuration of parent

$ kubectl delete namespace parent
# Should succeed

To set the allowCascadingDeletion field without the plugin, simply set the spec.allowCascadingDeletion field to true in the namespace's hierarchyconfiguration/hierarchy object - for example, via:

$ kubectl edit -nchild hierarchyconfiguration hierarchy

Organize full namespaces into a hierarchy

Most users will only interact with HNC’s hierarchy through subnamespaces. But you can also organize full namespaces - that is, any Kubernetes namespace that is not a subnamespace - into hierarchies as well. To do this, you need the “update” permission for HierarchyConfiguration objects on various namespaces, as will be described below. If you have the “update” permission of these objects, we call you an administrator of the namespace.

Imagine that ns-bar and ns-foo are two full namespaces that you created via kubectl create namespace, and you’d like ns-foo to be the parent of ns-bar. To do this using the kubectl plugin:

$ kubectl hns set ns-bar --parent ns-foo

To do this without the plugin, in ns-bar, edit the hierarchyconfiguration/hierarchy object and set its .spec.parent field to ns-foo.

In order to make this change, you need to be an administrator of both ns-foo and ns-bar. You need to be an admin for ns-bar since you’re changing its hierarchy, and of ns-foo because your namespace may start to inherit sensitive properties such as secrets from ns-foo.

If you decide that you no longer want ns-bar to be a child of ns-foo, you can do this as follows using the plugin:

$ kubectl hns set ns-bar --root

To do this without the plugin, in ns-bar, edit the hierarchyconfiguration/hierarchy object and delete its .spec.parent field.

In this example, ns-foo and ns-bar were both originally root namespaces - that is, they did not have any ancestors. However, if ns-bar had any ancestors, this changes the permissions you require to change the parent of ns-bar to ns-foo:

  • If ns-bar and ns-foo both have ancestors, but none in common: In effect, you are moving ns-bar out of one tree, and into another one. Put another way, anyone who was an administrator of the old tree will lose access to ns-bar. As a result, you must be an administrator of the “oldest” ancestor of ns-bar - that is, the root namespace that has ns-bar as a descendant. In the new tree, you still only need to be an administrator of ns-foo (the same as before) since you’re still only gaining access to information in that namespace.
  • If ns-bar and ns-foo have an ancestor in common: In this case, you are moving ns-bar around inside the tree containing both ns-bar and ns-foo. In this case, you must be an administrator of the most recent ancestor to both ns-bar and ns-foo.

Similarly, if you want to make ns-bar a root again, you must be an administrator of the root namespace that is an ancestor of ns-bar, since the admins of that namespace will lose access to ns-bar once it becomes a root.

Resolve conditions on a namespace

If the namespace has the following condition:

ActivitiesHalted (ParentMissing): Parent "<namespace>" does not exist

It means that this namespace is orphaned and its parent has been deleted. To fix this, you need to either create the parent, or mark this namespace as a root namespace by using:

$ kubectl hns set --root <namespace>

Limit the propagation of an object to descendant namespaces

To limit the propagation of an object, annotate it with an exception. You can use any of the following annotations:

  • propagate.hnc.x-k8s.io/select: The object will only be propagated to namespaces whose labels match the label selector. The value for this selector has to be a valid Kubernetes label selector.

  • propagate.hnc.x-k8s.io/treeSelect: Use a single namespace name to represent where this object should be propagated, or use a comma-separated list of negated (“!”) namespaces to represent which namespaces not to propagate to (e.g. !child1, !child2 means do not propagate to child1 and child2). For example, this can be used to propagate an object to a child namespace, but not a grand-child namespace, using the value child, !grand-child.

  • propagate.hnc.x-k8s.io/none: Setting none to true (case insensitive) will result in the object not propagating to any descendant namespace. Any other value will be rejected.

For example, consider a case with a parent namespace with three child namespaces, and the parent namespace has a secret called my-secret. To set my-secret propagate to child1 namespace (but nothing else), you can use:

kubectl annotate secret my-secret -n parent propagate.hnc.x-k8s.io/treeSelect=child1
# OR
kubectl annotate secret my-secret -n parent propagate.hnc.x-k8s.io/treeSelect="!child2, !child3"
# OR
kubectl annotate secret my-secret -n parent propagate.hnc.x-k8s.io/select=child1.tree.hnc.x-k8s.io/depth
# OR
kubectl annotate secret my-secret -n parent propagate.hnc.x-k8s.io/select="!child2.tree.hnc.x-k8s.io/depth, !child3.tree.hnc.x-k8s.io/depth"

To set my-secret not to propagate to any namespace, you can use:

kubectl annotate secret my-secret -n parent propagate.hnc.x-k8s.io/none=true

All these are equivalent to creating the object with the selector annotations:

cat << EOF | kubectl create -f -
apiVersion: v1
kind: Secret
metadata:
  annotations:
    propagate.hnc.x-k8s.io/treeSelect: child1
  name: my-secret
  namespace: parent
... other fields ...
EOF

Administer HNC

Install or upgrade HNC on a cluster

HNC requires Kubernetes v1.16 or later, since it relies on APIs (such as CRDs and webhooks) that were only introduced in v1.16.

There is no need to uninstall HNC before upgrading it unless specified in the release notes for that version.

Prerequisite

These prerequisites apply to HNC v0.8 and higher

Prior to installing HNC, add the hnc.x-k8s.io/excluded-namespaces label to your critical system namespaces:

kubectl label ns kube-system hnc.x-k8s.io/excluded-namespace=true
kubectl label ns kube-public hnc.x-k8s.io/excluded-namespace=true
kubectl label ns kube-node-lease hnc.x-k8s.io/excluded-namespace=true

Failure to do so may result in HNC being unable to start, and your cluster's operations being degraded until you delete HNC or apply the labels.

If you wish, you may also exclude additional namespaces from HNC, but be aware that only the three namespaces listed above can be excluded by default.

Install an official release and the kubectl plugin

The most recent official release is v0.8.0. Please see that page for release notes and installation instructions.

Install from source

These instructions assume you are installing on GKE and have a GCR repo. If you'd like to contribute instructions for other clouds, please do so!

# The GCP project of the GCR repo:
export PROJECT_ID=my-gcp-project

# A tag for the image you want to build (default is 'latest')
export HNC_IMG_TAG=test-img

# Build and deploy to the cluster identified by your current kubectl context. This will
# also build the kubectl-hns plugin and install it at # ${GOPATH}/bin/kubectl-hns;
# please ensure this path is in your PATH env var in order to use it.
make deploy

Uninstall HNC from a cluster

To temporarily disable HNC, simply delete its deployment and webhooks:

kubectl -n hnc-system delete deployment hnc-controller-manager
kubectl delete validatingwebhookconfiguration.admissionregistration.k8s.io hnc-validating-webhook-configuration

You may also completely delete HNC, including its CRDs and namespaces. However, this is a destructive process that results in some data loss. In particular, you will lose any cluster-wide configuration in your HNCConfiguration object, as well as any hierarchical relationships between different namespaces, excluding subnamespaces (subnamespace relationships are saved as annotations on the namespaces themselves, and so can be recreated when HNC is reinstalled).

To avoid data loss, consider backing up your HNC objects so they can later be restored.

Note that even though the subnamespace anchors are deleted during this process, the namespaces themselves will not be. HNC distinguishes between anchors that are being deleted "normally" and those that are being deleted because their CRD is being removed.

To completely delete HNC, including all non-subnamespace hierarchical relationships and configuration settings:

# Firstly, delete the CRDs. Some of the objects have finalizers on them, so
# if you delete the deployment first, the finalizers will never be removed
# and you won't be able to delete the objects without explicitly removing
# the finalizers first.
kubectl get crds | grep .hnc.x-k8s.io | awk '{print $1}' | xargs kubectl delete crd

# Delete the rest of HNC.
kubectl delete -f https://github.com/kubernetes-sigs/multi-tenancy/releases/download/hnc-${HNC_VERSION}/hnc-manager.yaml

Excluding namespaces from HNC

The following instructions are only required for HNC v0.8.x and higher

HNC installs a validating webhook on all objects in your cluster. If HNC itself is damaged or inaccessible, this could result in all changes to all objects in your cluster being rejected, making it difficult to repair your cluster or even re-install HNC.

In order to prevent HNC from damaging your cluster, you can exclude certain namespaces from some of HNC's webhooks. Excluded namespace cannot be the parent or child of any other namespace; any attempts to change the hierarchy of an excluded namespace, or create a subnamespace within it, will be rejected by HNC. However, the critical webhooks will not operate in the excluded namespace, protecting your cluster's stability.

In order to exclude namespaces from HNC before installing it:

  1. Add the hnc.x-k8s.io/excluded-namespace label with the value of true to all critical namespaces. At a minimum, this label should be applied to kube-system, kube-public, and kube-node-lease as described in the installation instructions, but you may add additional namespaces if you wish.
  2. Ensure that all the namespaces you have excluded are also listed in the argument list with the option --excluded-namespace. By default, the HNC manifests include all the critical system namespaces listed above, but you can exclude any namespace you like.
  3. Apply the HNC manifest.

To exclude an additional namespace from HNC after it has been installed, follow these steps:

  1. Add the namespace to the list of --excluded-namespace command line args.
  2. Apply the hnc.x-k8s.io/excluded-namespace=true label to the namespace.

If you attempt to apply the hnc.x-k8s.io/excluded-namespace label to any namespace that is not also listed in the command line args, HNC will not allow the change, or will remove the label when it is started. This prevents users with edit access to a single namespace from removing themselves from HNC without permission of the HNC administrator.

Backing up and restoring HNC data

If you need to completely uninstall HNC, but don't want to lose all your hierarchical data (other than your subnamespaces), you can backup the data before uninstalling HNC, and restore it afterwards. However, be warned -- this is a fairly manual and not entirely bulletproof process. As an alternative, you may wish to consider using an external source of truth (such as Git) to store your cluster-wide configuration and any full namespace hierarchical relationships.

To backup your data, export HNC's custom resources as follows:

# Save any nonstandard configuration:
kubectl get hncconfiguration config -oyaml > hncconfig.yaml

# Save any explicit hierarchies (not needed if you only have subnamespaces):
kubectl get hierarchyconfigurations -A -oyaml > structure.yaml

After HNC is reinstalled, it will recreate the HierarchicalConfiguration objects in every namespace, and may automatically create these objects even in some full namespaces as well (for example, in the parents of subnamespaces). In order for your backed-up objects to be restored properly, edit structure.yaml to delete the .metadata.uid and metadata.resourceVersion fields from each object prior to applying the file. It may also be convenient to delete the .metadata.selfLink field, which is alphabetically between the other two fields; this is safe.

Once you are ready, first reapply the cluster-wide configuration via kubectl apply -f hncconfig.yaml, and then the structural relationships via kubectl apply -f structure.yaml.

Finally, resolve any SubnamespaceAnchorMissing conditions. Type kubectl hns tree -A to identify all subnamespaces affected, by this condition, and then recreate recreate the anchors manually by typing kubectl hns create <subns> -n <parent>.

Administer who has access to HNC properties

HNC has three significant objects whose access administrators should carefully control:

  • The HNCConfiguration object. This is a single non-namespaced object (named config) that defines the behaviour of the entire cluster. It should only be modifiable by cluster administrators. In addition, since it may contain information about any namespace in the cluster, it should only be readable by users trusted with this information. This object is automatically created by HNC when it's installed.
  • The HierarchyConfiguration objects. There’s either zero or one of these in each namespace, with the name hierarchy if it exists. Any user with update access to this object is known as an administrator of that namespace and its subtree, and access should be granted carefully as a result.
  • The SubnamespaceAnchor objects. These are used to create subnamespaces. Generally speaking, access to create or read these objects should be granted quite freely to users to have permission to use other objects in a given namespace, since this allows them to use hierarchical namespaces to organize their objects. However, be aware that any ResourceQuota in the parent namespace will not apply to any subnamespaces.

Note: There are various projects underway to allow resource quotas to be applied to trees of namespaces. For example, see the Dec 3 2019 wg-multitenancy meeting. Contact wg-multitenancy if you need this feature.

It is important to note that just because a user created a subnamespace, that does not make them an administrator of that subnamespace. That requires someone to explicitly grant them the update permission for the HierarchyConfiguration object in that namespace. As a result, an unprivileged user who creates a subnamespace generally can’t delete it as well, since this would require them to set the allowCascadingDeletion property of the child namespace.

Modify the resources propagated by HNC

HNC is configured via the HNCConfiguration object. You can inspect this object directly via kubectl get -oyaml hncconfiguration config, or with the HNS plugin via kubectl hns config describe.

The most important type of configuration is the way each object type ("resource") is synchronized across namespace hierarchies. This is known as the "synchronization mode," and has the following options:

  • Propagate: propagates objects from ancestors to descendants and deletes obsolete descendants.
  • Remove: deletes all existing propagated copies, but does not touch source objects.
  • Ignore: stops modifying this resource. New or changed objects will not be propagated, and obsolete objects will not be deleted. The hnc.x-k8s.io/inherited-from label is not removed. Any unknown mode is treated as Ignore. This is the default if a resource is not listed at all in the config, except for RBAC roles and role bindings (see below).

HNC enforces roles and rolebindings RBAC resources to have Propagate mode. Thus they are omitted in the HNCConfiguration spec and only show up in the status. You can also set any Kubernetes resource to any of the propagation modes discussed above. To do so, you need permission to update the HNCConfiguration object.

You can view the current set of resources being propagated, along with statistics, by saying kubectl hns config describe, or alternatively kubectl get -oyaml hncconfiguration config. This object is automatically created for you when HNC is first installed.

To configure an object resource using the kubectl plugin:

# "--group" can be omitted if the resource is a core K8s resource
kubectl hns config set-resource [resource] --group [group] --mode [Propagate|Remove|Ignore]

For example:

kubectl hns config set-resource secrets --mode Propagate

To verify that this worked:

kubectl hns config describe

# Output:
Synchronized types:
* Propagating: roles (rbac.authorization.k8s.io/v1)
* Propagating: rolebindings (rbac.authorization.k8s.io/v1)
* Propagating: secrets (v1) # <<<< This should be added

You can also modify the config directly to include custom configurations via kubectl edit hncconfiguration config:

apiVersion: hnc.x-k8s.io/v1alpha2
kind: HNCConfiguration
metadata:
  name: config
spec:
  resources:
    # Spec for other resources
    ...
    - resource: secrets   <<< This should be added
      mode: Propagate     <<<

Adding a new resource in the Propagate mode is potentially dangerous, since there could be existing objects of that resource type that would be overwritten by objects of the same name from ancestor namespaces. As a result, the HNS plugin will not allow you to add a new resource directly in the Propagate mode. Instead, to do so safely:

  • Add the new resource in the Remove mode. This will remove any propagated copies (of which there should be none) but will force HNC to start synchronizing all known source objects.
  • Wait until kubectl hns config describe looks like it's identified the correct number of objects of the newly added resource in its status.
  • Change the propagation mode from Remove to Propagate. HNC will then check to see if any objects will be overwritten, and will not allow you to change the propagation mode until all such conflicts are resolved.

Alternatively, if you're certain you want to start propagating objects immediately, you can use the --force flag with kubectl hns config set-resource to add a resource directly in the Propagate mode. You can also edit the config object directly, which will bypass this protection.

Gather metrics

HNC makes the following metrics available, and can be monitored via Stackdriver (next section) or Prometheus (experimental - see #433).

Our best practices guide can help you use these metrics to ensure that HNC stays healthy.

Metric Description
hnc/namespace_conditions The number of namespaces affected by conditions, tagged with information about the condition
hnc/reconcilers/hierconfig/total The total number of HierarchyConfiguration (HC) reconciliations happened
hnc/reconcilers/hierconfig/concurrent_peak The peak concurrent HC reconciliations happened in the past 60s, which is also the minimum Stackdriver reporting period and the one we're using
hnc/reconcilers/hierconfig/hierconfig_writes_total The number of HC writes happened during HC reconciliations
hnc/reconcilers/hierconfig/namespace_writes_total The number of namespace writes happened during HC reconciliations
hnc/reconcilers/object/total The total number of object reconciliations happened
hnc/reconcilers/object/concurrent_peak The peak concurrent object reconciliations happened in the past 60s, which is also the minimum Stackdriver reporting period and the one we're using

Use Stackdriver on GKE

To view HNC Metrics in Stackdriver, you will need a GKE cluster with HNC installed and a method to access Cloud APIs, specifically Stackdriver monitoring APIs, from GKE. We recommend using Workload Identity to minimize the permissions required to log metrics. Once it's set up, you can view the metrics in Stackdriver Metrics Explorer by searching the metrics keywords (e.g. namespace_conditions).

In order to monitor metrics via Stackdriver:

  1. Save your some key information as environment variables. You may adjust these values to suit your needs; there's nothing magical about them. 
    GSA_NAME=hnc-metric-writer
PROJECT_ID=my-gcp-project
  2. Enable Workload Identity (WI) on either a new or existing cluster.
  3. Install HNC as described above.
  4. Create a Google service account (GSA): 
    gcloud iam service-accounts create ${GSA_NAME}
  5. Grant “Monitoring Metric Writer” role to the GSA: 
    gcloud projects add-iam-policy-binding ${PROJECT_ID} --member \
  "serviceAccount:${GSA_NAME}@${PROJECT_ID}.iam.gserviceaccount.com" \
  --role "roles/monitoring.metricWriter"
  6. Create an Cloud IAM policy binding between hnc-system/default KSA and the newly created GSA: 
    gcloud iam service-accounts add-iam-policy-binding \
  --role roles/iam.workloadIdentityUser \
  --member "serviceAccount:${PROJECT_ID}.svc.id.goog[hnc-system/default]" \
  ${GSA_NAME}@${PROJECT_ID}.iam.gserviceaccount.com
  7. Add the iam.gke.io/gcp-service-account=${GSA_NAME}@${PROJECT_ID} annotation to the KSA, using the email address of the Google service account: 
    kubectl annotate serviceaccount \
  --namespace hnc-system \
  default \
  iam.gke.io/gcp-service-account=${GSA_NAME}@${PROJECT_ID}.iam.gserviceaccount.com

If everything is working properly, you should start to see metrics in the Stackdriver metrics explorer from HNC. Otherwise, you can inspect the service account configuration by creating a Pod with the Kubernetes service account that runs the cloud-sdk container image, and connecting to it with an interactive session:

kubectl run --rm -it \
  --generator=run-pod/v1 \
  --image google/cloud-sdk:slim \
  --serviceaccount default \
  --namespace hnc-system \
  workload-identity-test

# Inside the new pod:

gcloud auth list

Modify command-line arguments

HNC's default manifest file (available as part of each release with the name hnc-manager.yaml) includes a set of reasonable default command-line arguments for HNC. These parameters are part of the hnc-controller-manager Deployment object in the hnc-system namespace.

To modify these parameters, you may:

  • Modify the manifest file and re-apply it with kubectl apply -f
  • Directly edit the Deployment via kubectl edit -n hnc-system deploy hnc-controller-manager.

Note that these parameters are different from those controlled by HNCConfiguration - they should only be modified extremely rarely, and only with significant caution.

Interesting parameters include:

  • --excluded-namespace=<namespace>: allows you to exclude a namespace from HNC.
  • --unpropagated-annotation=<string>: empty by default, this argument can be specified multiple times, with each parameter representing an annotation name, such as example.com/foo. When HNC propagates objects from ancestor to descendant namespaces, it will strip these annotations out of the metadata of the copy of the object, if it exists. For example, this can be used to remove an annotation on the source object that's has a special meaning to another system, such as GKE Config Sync. If you restart HNC after changing this arg, all existing propagated objects will also be updated.
  • --apiserver-qps-throttle=<integer>: set to 50 by default, this limits how many requests HNC will send to the Kubernetes apiserver per second in the steady state (it may briefly allow up to 50% more than this number). Setting this value too high can overwhelm the apiserver and prevent it from serving requests from other clients. HNC can easily generate a huge number of requests, especially when it's first starting up, as it tries to sync every namespace and every propagated object type on your cluster.
  • --enable-internal-cert-management: present by default. This option uses the ODA cert-controller library to create and distribute the HTTPS certificates used by HNC's webhooks. If you remove this parameter, you can replace it with external cert management, such as Jetstack's cert-manager, which must be separately deployed, configured and maintained.
  • --suppress-object-tags: present by default. If removed, many more tags are included in the metrics produced by HNC, including the names of personally identifiable information (PII) such as the names of the resource types. This can give you more insight into HNC's behaviour at the cost of an increased load on your metrics database (through increased metric cardinality) and also by increasing how carefully you need to guard your metrics against unauthorized viewers.