Reconnection policies

Reconnection policies allow the DataStax drivers to automatically reestablish a connection to a node that was previously marked as down.

Reconnection policies allow the DataStax drivers to automatically reestablish a connection to a node that was previously marked as down. A node can be marked down by the server's gossip process or as a result of an idle connection timeout. Status changes are passed along the control connection back to the driver.

All of the drivers offer a standard reconnection policy. Some drivers offer additional reconnection policies:

Constant: The driver waits a constant amount of time between each reconnection attempt.
Exponential: The driver waits exponentially longer between each reconnection attempt.
Fixed: The driver waits a different amount of time between each reconnection attempt.

Note: Drivers that offer the exponential reconnection policy use that policy as their default. For other drivers, the constant reconnection policy is the default policy.

Table 1. Reconnection policies for drivers
C/C++	C#	Java	Node.js	PHP	Python	Ruby

Gossip reconnection

The control connection for the drivers listens to push notifications from the DSE server cluster. When a node is marked up, all scheduled reconnections are canceled and a new connection to that node is established.

Idle disconnect and reconnection

To prevent intermediate network devices like routers and firewalls from disconnecting the drivers from a node, an OPTIONS request is sent to a connection at a constant interval, also known as a heartbeat. If the connection becomes idle and the node does not respond to the heartbeat in a given amount of time, the node is marked down. Once this occurs, the driver waits a specified amount of time based on the reconnection policy before attempting to reconnect to the node.