When a new pod is created (via deployment) the creation is intercepted by a MutationWebhookConfiguration. The actual web server handling webhook requests is the OSM pod itself. A request to create a new pod results in a patch operation adding the Envoy sidecar. The webhook handler server creates a bootstrap configuration for the Envoy proxy with two critical components:
- address of the XDS server (this is the OSM pod itself)
- mTLS certificate to connect to XDS (this certificate is different than the service-to-service certificates issued by OSM)
The webhook server also generates a UUID for the pod and the pod is labeled with it. The UUID is also used in the certificate. This UUID links the pod and the certificate.
The Envoy bootstrap certificate issued has a CN of the following format:
pod-uuid is a UUID generated by the webhook handler. This UUID is added as a label to the pod as well as in the certificate CN. The key for the Pod label is unique to the OSM instance.
When the Envoy proxy connects to xDS it presents the client certificate. OSM / xDS parses the certificate and from the pod UUID and the namespace (obtained from the cert CN) fetches the Kubernetes Pod object. From the Pod object OSM determines ServiceAccount and Service belonging. Based on this context and SMI policies, OSM generates Envoy config.
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