// listenForNodeChanges listens for changes to node status using change feeds.
// This function will block until the query fails
func (c *Cluster) listenForNodeChanges() error {
// Start listening to changes from a random active node
node, err := c.GetRandomNode()
if err != nil {
return err
}
q, err := newQuery(
DB("rethinkdb").Table("server_status").Changes(),
map[string]interface{}{},
c.opts,
)
if err != nil {
return fmt.Errorf("Error building query %s", err)
}
cursor, err := node.Query(q)
if err != nil {
return err
}
// Keep reading node status updates from changefeed
var result struct {
NewVal nodeStatus `gorethink:"new_val"`
OldVal nodeStatus `gorethink:"old_val"`
}
for cursor.Next(&result) {
addr := fmt.Sprintf("%s:%d", result.NewVal.Network.Hostname, result.NewVal.Network.ReqlPort)
addr = strings.ToLower(addr)
switch result.NewVal.Status {
case "connected":
// Connect to node using exponential backoff (give up after waiting 5s)
// to give the node time to start-up.
b := backoff.NewExponentialBackOff()
b.MaxElapsedTime = time.Second * 5
backoff.Retry(func() error {
node, err := c.connectNodeWithStatus(result.NewVal)
if err == nil {
if !c.nodeExists(node) {
c.addNode(node)
Log.WithFields(logrus.Fields{
"id": node.ID,
"host": node.Host.String(),
}).Debug("Connected to node")
}
}
return err
}, b)
}
}
return cursor.Err()
}
// discover attempts to find new nodes in the cluster using the current nodes
func (c *Cluster) discover() {
// Keep retrying with exponential backoff.
b := backoff.NewExponentialBackOff()
// Never finish retrying (max interval is still 60s)
b.MaxElapsedTime = 0
// Keep trying to discover new nodes
for {
backoff.RetryNotify(func() error {
// If no hosts try seeding nodes
if len(c.GetNodes()) == 0 {
c.connectNodes(c.getSeeds())
}
return c.listenForNodeChanges()
}, b, func(err error, wait time.Duration) {
Log.Debugf("Error discovering hosts %s, waiting %s", err, wait)
})
}
}