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# Auto restart of pods when secret is rotated | ||
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_This is a suggested implementation which can be used alongside the Secrets Store CSI Driver._ | ||
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When [auto rotation of secrets](./secret-auto-rotation.md) is enabled, workloads which depend upon secrets will need to either | ||
- watch for updates to secrets and reload these in their runtime, or | ||
- be restarted to pick up the latest secrets when they change | ||
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A solution such as [Reloader](https://github.com/stakater/Reloader) could be used to watch for updates to Kubernetes Secrets or ConfigMaps and restart pods when a change is detected. However, if secret values are mounted as volumes in the pods, that solution is not suitable. | ||
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Using custom resources created by the Secrets Store CSI Driver, a Kubernetes Controller can be used to detect when secrets are updated by the driver and to restart affected pods. | ||
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## SecretProviderClassPodStatus custom resource | ||
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The relevant custom resource is [`SecretProviderClassPodStatus`](https://secrets-store-csi-driver.sigs.k8s.io/concepts#secretproviderclasspodstatus). | ||
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Each `SecretProviderClassPodStatus` CR has a one-to-one relationship with a pod which references secrets using the Secrets Store CSI Driver. The CR identifies the pod name, namespace and other attributes. The driver manages the lifecyle of `SecretProviderClassPodStatus` which is linked to the lifecycle of the affected pod. | ||
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```mermaid | ||
stateDiagram-v2 | ||
state "SecretProviderClassPodStatus\nGeneration: 1" as g1 | ||
state "SecretProviderClassPodStatus\nGeneration: n" as gn | ||
[*] --> g1: pod create with secret from csi | ||
g1 --> gn: secret updated in pod | ||
gn --> [*]: pod restart | ||
``` | ||
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When the driver sets a secret value for a new pod, a `SecretProviderClassPodStatus` CR is created with the `Generation` attribute set to `1`. | ||
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Whenever the driver updates the secret value, the value of the `Generation` attribute is incremented. | ||
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If a pod is restarted, the CR is deleted and a new CR created with `Generation: 1`. | ||
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`SecretProviderClassPodStatus` CRs persist across lifetimes of the secrets-store-csi-driver. | ||
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## Outline of Controller function | ||
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1. Reconcile | ||
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The controller reconciles instances of the `SecretProviderClassPodStatus` CR and deletes (to restart) the associated pod if required. | ||
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If a `SecretProviderClassPodStatus` has `Generation: 1`, it is linked to a newly created pod. The pod should not be restarted. | ||
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If a `SecretProviderClassPodStatus` has `Generation` > 1, it is linked to a pod in which the secrets-store-csi-driver has updated a secret. The pod should be restarted (if it has opted-in for automatic restarting). | ||
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1. Rolling restart | ||
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On reconciling a pod which should be updated, check `metadata.ownerReferences` and walk up to a Deployment (or similar) if present. | ||
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If a `Deployment` is found: | ||
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- Do not restart pod | ||
- Update the Deployment to trigger a rolling restart | ||
- If the number of replicas > 1, update the Deployment once only | ||
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To restart a deployment, the controller sets a timestamped annotation in the deployment | ||
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``` | ||
template: | ||
metadata: | ||
annotations: | ||
my.controller/restartedAt: "2024-09-05T14:06:29Z" | ||
``` | ||
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Else: delete pod. | ||
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1. Opt-in to automatic pod restarting | ||
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Automatic restarting of pods when secrets are updated could be an opt-in behaviour. Unless the pod declares its opt-in, it should not be restarted by the controller. | ||
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The opt-in could be indicated via an optional annotation set on the pod: | ||
``` | ||
kind: pod | ||
metadata: | ||
annotations: | ||
my.controller/restartOnChange: true | ||
``` | ||
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## Implementation notes | ||
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The [operator-sdk](https://github.com/operator-framework/operator-sdk) can be used to scaffold an implementation project. | ||
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1. Scaffolding the project | ||
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``` | ||
operator-sdk init --repo=<your repo> | ||
operator-sdk create api --version v1alpha1 --kind SecretProviderClassPodStatus --resource=false --controller=true | ||
``` | ||
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1. Custom resources | ||
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The controller does not manage custom resources of its own. It simply watches a custom resource provided by the Secrets Store CSI Driver. | ||
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1. Permissions required | ||
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The controller requires RBAC permissions to operate on various k8s resources. | ||
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To watch `SecretProviderClassPodStatus` | ||
``` | ||
// +kubebuilder:rbac:groups=secrets-store.csi.x-k8s.io,resources=secretproviderclasspodstatuses,verbs=get;list;watch | ||
``` | ||
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To lookup and if necessary delete `Pod` | ||
``` | ||
// +kubebuilder:rbac:groups="",resources=pods,verbs=get;list;watch;delete | ||
``` | ||
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To lookup possible owner of `Pod` | ||
``` | ||
// +kubebuilder:rbac:groups="apps",resources=daemonsets,verbs=get;list;watch | ||
// +kubebuilder:rbac:groups="apps",resources=replicasets,verbs=get;list;watch | ||
// +kubebuilder:rbac:groups="apps",resources=statefulsets,verbs=get;list;watch | ||
// +kubebuilder:rbac:groups="apps",resources=deployments,verbs=get;list;watch | ||
``` | ||
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To lookup and if necessary trigger update of `Deployment` | ||
``` | ||
// +kubebuilder:rbac:groups="apps",resources=deployments,verbs=get;list;watch;update | ||
``` |