Service B initiates the connection to Service A in order to receive notifications, and Service B initiates the connection to Service A to query for changed data.
Service A never initiates a connection with Service B. If Service B went offline, Service A would never notice.
Service B initiates the connection to Service A in order to receive notifications, and Service B initiates the connection to Service A to query for changed data.
Service A never initiates a connection with Service B. If Service B went offline, Service A would never notice.