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43 lines
2.3 KiB
Markdown
43 lines
2.3 KiB
Markdown
# Kubernetes Mutating Webhook for ImagePullSecret injection in ServiceAccounts
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The responsibility of this webhook is to patch all newly created/updated service account and make sure they all contained proper imagepullsecret configuration.
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## Helm description
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The helm chart consists of 2 parts: the certificate generator and the webhook configuration itself.
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Certificate generation part periodically generates certificates signed by kubernetes' CA and passes them to the webhook where they are used as server-side certificates. The flow works roughly like this:
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1. We generate a CSR using openssl and tie the certificate to the webhook's service DNS.
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1. We create a k8s CertificateSigningRequest from the openssl CSR.
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1. We approve this request using our special ServiceAccount with approve permissions. This makes kubernetes issue the certificate
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1. We fetch the certificate from the k8s CSR (at `.status.certificate`) and create a secret from it
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1. We also create a CronJob that does this periodically as k8s only issues certificates for 1 year
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The main part is the deployment and the web hook configuration. The flow is as follows
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1. The MutatingWebhookConfiguration we create instructs k8s to pass all requests for creating/updating all ServiceAccounts to our webhook before finishing the request
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1. We check whether the SA has the correctly defined imagepullsecret configuration. if not, we create a patch for the resource
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1. We also check whether we have the secret we are using in the imagepullsecret in the SA's namespace. If not, we create it based on our source secret
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1. We return the patch to k8s, which applies the changes
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Of note is also a fact that the chart runs a lookup to the connected cluster to fetch the CA bundle for the MutatingWebhook. This means `helm template` won't work.
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## Running locally
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```bash
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kubectl create ns imagepullsecret-injector
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kubectl create secret -n imagepullsecret-injector \
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generic my-cool-secret-source \
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--from-literal=.dockerconfigjson='<your .dockerconfigjson configuration file>'
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make build-image
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helm upgrade -i imagepullsecret-injector \
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--create-namespace -n imagepullsecret-injector \
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helm/imagepullsecret-injector
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```
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To test whether everything works, you can run
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```bash
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kubectl create ns yolo
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kubectl get sa -n yolo default -ojsonpath='{.imagePullSecrets}'
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```
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The get command should display _some_ non-empty result.
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