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