stunnel: sessiond

sessiond allows a cluster of SSL/TLS servers to share their session caches in order to prevent each node of the cluster from negotiating a separate session. SSL/TLS session is basically a set of secret values (symmetric encryption keys, MAC secrets) shared between a client and a server. The use of asymmetric cryptography required to establish new sessions is the main performance bottleneck of the SSL/TLS protocol.

sessiond takes the port number as a parameter. The default port is 54321.

The timeout is currently hardcoded to 200ms. It seems to be a reasonable value to allow uninterrupted operation in case of sessiond server failure or a lost packet.

There is no encryption of sessiond traffic, as the network infrastructure within a cluster is usually trusted.

Security requirements for the infrastructure:
  • sessiond port must not be accessible from untrusted networks
  • network traffic between stunnel and sessiond must only be accessible by trusted personnel

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