Draining, Disabling, or Removing a Node

You might occasionally want to remove one of your back-end nodes from your load-balanced server farm. This could be permanent, or a temporary measure to allow for maintenance or upgrade.

Choose to either "disable" or "drain" the node, such that the Traffic Manager does not send any new requests, or just remove the node completely from the pool:

•Disable a node: Stops the Traffic Manager sending any more connections to the node. The node remains present in the pool configuration, although the Traffic Manager ceases monitoring it. For more details, see Disabling a Node.

•Drain a node: Stops the Traffic Manager sending any more new connections to the node, but honors established sessions. The Traffic Manager continues to actively monitor the node. For more details, see Draining a Node.

•Remove a node: Permanently removes the node from the pool configuration. For more details, see Removing Nodes From a Pool.

To disable, drain, or remove a node from a pool, use the Services > Pools > Edit page. Edit a pool containing the node and change the node status to “Disabled” or “Draining” as required. To remove the node, tick the adjacent Delete checkbox. To save your changes, click Update.

This process only drains, disables, or removes the node for that particular pool. Any other pools using the same node are unaffected.

Using the Node Wizards

To simplify the processes of disabling, draining, reactivating, or removing nodes across a range of your services, the Traffic Manager provides a series of wizards. To access the wizards, use the Wizards menu in the top tool bar:

•Disable a node

•Drain a node

•Reactivate a node

•Remove a node

You specify a node to drain/disable (depending on the wizard chosen), and choose whether to apply this for all services or just those you specify. You can restore the node to active status later using the Reactivate a node wizard. To remove a node completely from one or all of your services, use the Remove a node wizard.

Disabling a Node

Consider disabling a node if you plan to take it out of service temporarily. Existing connections to the node are handled according to the settings discussed in Altering the Behavior of Existing Connections when Disabling or Removing a Node. If the node stops working (for example, because you shut down the server), the Traffic Manager does not report an error. The advantage of disabling a node rather than removing it from the configuration is that a disabled node can easily be re-instated when it is ready to be used.

Draining a Node

Consider draining a node if you are concerned about existing sessions, but bear in mind that if the node stops working, the Traffic Manager reports an error. If the Traffic Manager receives a request and session persistence requires that the node is used, the Traffic Manager continues to use it. If you plan to shut the node down, you should drain it first, waiting until all sessions have completed, then disable it.

To find out whether the node is still handling connections, click Activity > Draining Nodes. This page shows the number of connections the node is still handling, and the time since the last connection. For more details, see Draining Connections. When the node’s existing connections have expired, you can disable it, or use the Remove a Node wizard to remove it cleanly from your cluster.

Removing Nodes From a Pool

If you plan to retire one or more server nodes from the pool permanently, and have no requirement to retain any corresponding configuration, delete the nodes from the pool. Existing connections to the node are handled according to the settings discussed in Altering the Behavior of Existing Connections when Disabling or Removing a Node.

If you attempt to remove all nodes from the pool, the Admin UI issues a warning that no new traffic can be received by the pool, and requires explicit consent before this action is completed. To override the warning, tick the confirmation checkbox adjacent to the Update button and try again.

Altering the Behavior of Existing Connections when Disabling or Removing a Node

The behavior of existing connections to nodes that you either disable or remove is dependent on the value of node_delete_behavior (found in Services > Pools > Edit > Protocol Settings). This setting has two options:

•All connections to the node are closed immediately: the Traffic Manager terminates all connections to the node immediately.

•Allow existing connections to the node to finish before deletion: any node that is disabled or removed while it has existing connections is kept in a "Draining"-like state, until it is automatically disabled or removed at the earliest occurrence of one of the following events:

•its connection count dropping to zero

•the value of node_drain_to_delete_timeout (found in Services > Pools > Edit > Protocol Settings) being reached (if non-zero).

Such draining nodes are included in the list at Activity > Draining Nodes, with "Yes" in the "Autodelete" column.