In certain circumstances an administrator might not want to disconnect
all clients immediately when stopping the broker. In this situation the
broker can be configured to shutdown gracefully using the
graceful-shutdown-enabled boolean configuration parameter.
When the graceful-shutdown-enabled configuration parameter is true
and the broker is shutdown it will first prevent any additional clients
from connecting and then it will wait for any existing connections to
be terminated by the client before completing the shutdown process. The
default value is false.
Of course, it's possible a client could keep a connection to the broker
indefinitely effectively preventing the broker from shutting down
gracefully. To deal with this of situation the
graceful-shutdown-timeout configuration parameter is available. This
tells the broker (in milliseconds) how long to wait for all clients to
disconnect before forcefully disconnecting the clients and proceeding
with the shutdown process. The default value is -1 which means the
broker will wait indefinitely for clients to disconnect.