Persistent subscriptions are configured on the SR OS node and they are not cleared when the gRPC session terminates. Persistent subscriptions are supported only in dial-out mode.
A persistent subscription associates one or more paths with corresponding destinations via sensor groups.
Every subscription has an associated administrative state as well as an operational state. If a connection is lost, the operational state goes down. If the collector does not receive the data but the SR OS appears to have a connection and the subscription is up, the connection can be reset by setting the administrative state down and then back up.
Destinations are defined in the form of destination groups. A destination group supports up to two destinations, where the destinations are served in a round-robin fashion. SR OS attempts to connect the first destination, and if successful, the telemetry data is sent to that destination. If the connection to the first destination fails (initially or during operation), SR OS attempts to connect or reconnect to the second destination, if it is configured. All configured destinations and local addresses should be reachable in the specified routing instances.
When the SR OS node initiates the gRPC connection via the Publish RPC, it includes the subscription name and the configured system name in the metadata. The collector can use this information to associate individual notification messages with the node and subscription.
Modifying any parameter of the active subscription causes the SR OS node to close the gRPC connection before attempting a reconnection.
When a gRPC connection is lost, the SR OS node continually attempts to establish a new session with the collector.