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TLS topology in Tectonic

Secure communication in Tectonic is governed by three certificate authorities (CAs) etcd, kube, and ingress for cluster internal and external TLS traffic.

  • etcd: secures the communication from the API server as well as between peer etcd nodes.
  • kube/identity: secures the communication to the API server as well as to the Tectonic Identity grpc communication.
  • ingress: secures the communication to the Tectonic Ingress, effectively also securing access to the Tectonic Console as well as to the Tectonic Identity OIDC endpoint.

The following diagram illustrates which CAs are responsible for which communication paths:

CA topology

The above CA topology is reflected in the the corresponding Terraform modules modules/tls/etcd, modules/tls/identity, modules/tls/ingress, and modules/tls/kube.

Each of the above TLS modules comes in two flavors:

  • self-signed: All necessary certificates (potentially also including the CA certificate/key pair) are self-signed.
  • user-provided: All necessary certificates are provided by the user pointing to file locations of the corresponding certificates and/or keys.

Note that the behavior of the above flavors is "polymorphic". All flavors for a given TLS module have potentially different inputs, but they share the same outputs. The goal of this invariant is to be able to swap out/swap in a flavor of a given TLS module without the necessity to change any of its dependencies.

The following overview lists outputs of all TLS modules and their corresponding function.

etcd

Terraform module: modules/tls/etcd

etcd → etcd peer communication:

Certificate/Key etcd parameter Description
etcd_ca_crt_pem --peer-trusted-ca etcd CA cert
etcd_peer_crt_pem --etcd-certfile etcd peer cert
etcd_peer_key_pem --etcd-keyfile etcd peer key

API → etcd client/server communication:

Certificate/Key API server parameter etcd parameter Description
etcd_ca_crt_pem --etcd-cafile   etcd CA cert
etcd_client_crt_pem --etcd-certfile   API client cert
etcd_client_key_pem --etcd-keyfile   API client key
etcd_server_crt_pem   --cert-file etcd server cert
etcd_server_key_pem   --key-file etcd server key

Note: In contrast to other TLS modules the signed flavor for the etcd TLS module doesn't have the self- prefix, because in contrast to all other TLS modules, an external etcd CA cert/key can be provided which is used to sign certificates and/or keys.

Kube CA (cluster communication)

Terraform module: modules/tls/kube

Control plane → API

Certificate/Key API server parameter Description
ca_cert_pem --tls-ca-file secure access from Admission Controllers
apiserver_cert_pem --tls-cert-file https server cert
apiserver_key_pem --tls-private-key-file https server key

API → Kubelet

Certificate/Key API server parameter kubelet parameter Description
ca_cert_pem   --client-ca-file client cert CA
apiserver_cert_pem --kubelect-client-certificate   kubelect client cert
apiserver_key_pem --kubelet-client-key   kubelet client key

Kube CA (identity communication)

Terraform module: modules/tls/identity

Tectonic Console → Tectonic Identity

Certificate/Key Tectonic Console env var Tectonic Identity config Description
client_cert_pem BRIDGE_DEX_CLIENT_CERT_FILE   grpc client cert
client_key_pem BRIDGE_DEX_CLIENT_KEY_FILE   grpc client key
server_key_pem   grpc.tlsKey grpc server key
server_cert_pem   grpc.tlsCert grpc server cert
ca_cert_pem   grpc.tlsClientCA grpc client CA

Note: ca_cert_pem is sourced from modules/tls/kube. The Tectonic Identity config refers to the tectonic-identity ConfigMap in modules/tectonic/resources/manifests/identity/configmap.yaml.

Ingress CA

Terraform module: modules/tls/ingress

Users -> Identity

Certificate/Key Tectonic Console env var Tectonic Ingress Controller Description
ca_cert_pem BRIDGE_CA_FILE   ingress CA cert
cert_pem   --default-ssl-certificate ingress server cert
key_pem   --default-ssl-certificate ingress server key

API -> Identity

Certificate/Key Tectonic Console env var Description
ca_cert_pem --oidc-ca-file ingress CA cert