Improve etcd load-balancer startup behavior

Prefer the address of the etcd member being joined, and seed the full address list immediately on startup.

Signed-off-by: Brad Davidson <brad.davidson@rancher.com>

pkg/cluster/cluster.go

@@ -43,23 +43,37 @@ func (c *Cluster) Start(ctx context.Context) (<-chan struct{}, error) {
 		ready := make(chan struct{})
 		defer close(ready)
 
-		// try to get /db/info urls first before attempting to use join url
+		// try to get /db/info urls first, for a current list of etcd cluster member client URLs
 		clientURLs, _, err := etcd.ClientURLs(ctx, c.clientAccessInfo, c.config.PrivateIP)
 		if err != nil {
 			return nil, err
 		}
-		if len(clientURLs) < 1 {
+		// If we somehow got no error but also no client URLs, just use the address of the server we're joining
+		if len(clientURLs) == 0 {
 			clientURL, err := url.Parse(c.config.JoinURL)
 			if err != nil {
 				return nil, err
 			}
 			clientURL.Host = clientURL.Hostname() + ":2379"
 			clientURLs = append(clientURLs, clientURL.String())
+			logrus.Warnf("Got empty etcd ClientURL list; using server URL %s", clientURL)
 		}
 		etcdProxy, err := etcd.NewETCDProxy(ctx, c.config.SupervisorPort, c.config.DataDir, clientURLs[0], utilsnet.IsIPv6CIDR(c.config.ServiceIPRanges[0]))
 		if err != nil {
 			return nil, err
 		}
+		// immediately update the load balancer with all etcd addresses
+		// client URLs are a full URI, but the proxy only wants host:port
+		for i, c := range clientURLs {
+			u, err := url.Parse(c)
+			if err != nil {
+				return nil, errors.Wrap(err, "failed to parse etcd ClientURL")
+			}
+			clientURLs[i] = u.Host
+		}
+		etcdProxy.Update(clientURLs)
+
+		// start periodic endpoint sync goroutine
 		c.setupEtcdProxy(ctx, etcdProxy)
 
 		// remove etcd member if it exists

pkg/cluster/managed.go

@@ -17,6 +17,7 @@ import (
 	"github.com/k3s-io/k3s/pkg/version"
 	"github.com/sirupsen/logrus"
 	apierrors "k8s.io/apimachinery/pkg/api/errors"
+	"k8s.io/apimachinery/pkg/util/wait"
 )
 
 // testClusterDB returns a channel that will be closed when the datastore connection is available.
@@ -132,28 +133,25 @@ func (c *Cluster) setupEtcdProxy(ctx context.Context, etcdProxy etcd.Proxy) {
 	if c.managedDB == nil {
 		return
 	}
-	go func() {
-		t := time.NewTicker(30 * time.Second)
-		defer t.Stop()
-		for range t.C {
-			newAddresses, err := c.managedDB.GetMembersClientURLs(ctx)
+	// We use Poll here instead of Until because we want to wait the interval before running the function.
+	go wait.PollUntilWithContext(ctx, 30*time.Second, func(ctx context.Context) (bool, error) {
+		clientURLs, err := c.managedDB.GetMembersClientURLs(ctx)
 		if err != nil {
-				logrus.Warnf("Failed to get etcd client URLs: %v", err)
-				continue
+			logrus.Warnf("Failed to get etcd ClientURLs: %v", err)
+			return false, nil
 		}
 		// client URLs are a full URI, but the proxy only wants host:port
-			var hosts []string
-			for _, address := range newAddresses {
-				u, err := url.Parse(address)
+		for i, c := range clientURLs {
+			u, err := url.Parse(c)
 			if err != nil {
-					logrus.Warnf("Failed to parse etcd client URL: %v", err)
-					continue
+				logrus.Warnf("Failed to parse etcd ClientURL: %v", err)
+				return false, nil
 			}
-				hosts = append(hosts, u.Host)
+			clientURLs[i] = u.Host
 		}
-			etcdProxy.Update(hosts)
-		}
-	}()
+		etcdProxy.Update(clientURLs)
+		return false, nil
+	})
 }
 
 // deleteNodePasswdSecret wipes out the node password secret after restoration

pkg/etcd/etcd.go

@@ -725,7 +725,6 @@ func getClientConfig(ctx context.Context, control *config.Control, endpoints ...
 		DialTimeout:          defaultDialTimeout,
 		DialKeepAliveTime:    defaultKeepAliveTime,
 		DialKeepAliveTimeout: defaultKeepAliveTimeout,
-		AutoSyncInterval:     defaultKeepAliveTimeout,
 		PermitWithoutStream:  true,
 	}
 
@@ -1387,36 +1386,51 @@ func (e *ETCD) defragment(ctx context.Context) error {
 // The list is retrieved from the remote server that is being joined.
 func ClientURLs(ctx context.Context, clientAccessInfo *clientaccess.Info, selfIP string) ([]string, Members, error) {
 	var memberList Members
-	resp, err := clientAccessInfo.Get("/db/info")
-	if err != nil {
-		return nil, memberList, &MemberListError{Err: err}
-	}
 
-	if err := json.Unmarshal(resp, &memberList); err != nil {
-		return nil, memberList, err
-	}
+	// find the address advertised for our own client URL, so that we don't connect to ourselves
 	ip, err := getAdvertiseAddress(selfIP)
 	if err != nil {
 		return nil, memberList, err
 	}
-	var clientURLs []string
-members:
-	for _, member := range memberList.Members {
-		// excluding learner member from the client list
-		if member.IsLearner {
-			continue
-		}
-		for _, clientURL := range member.ClientURLs {
-			u, err := url.Parse(clientURL)
+
+	// find the client URL of the server we're joining, so we can prioritize it
+	joinURL, err := url.Parse(clientAccessInfo.BaseURL)
 	if err != nil {
-				continue
+		return nil, memberList, err
 	}
-			if u.Hostname() == ip {
-				continue members
+
+	// get the full list from the server we're joining
+	resp, err := clientAccessInfo.Get("/db/info")
+	if err != nil {
+		return nil, memberList, &MemberListError{Err: err}
+	}
+	if err := json.Unmarshal(resp, &memberList); err != nil {
+		return nil, memberList, err
+	}
+
+	// Build a list of client URLs. Learners and the current node are excluded;
+	// the server we're joining is listed first if found.
+	var clientURLs []string
+	for _, member := range memberList.Members {
+		var isSelf, isPreferred bool
+		for _, clientURL := range member.ClientURLs {
+			if u, err := url.Parse(clientURL); err == nil {
+				switch u.Hostname() {
+				case ip:
+					isSelf = true
+				case joinURL.Hostname():
+					isPreferred = true
 				}
 			}
+		}
+		if !member.IsLearner && !isSelf {
+			if isPreferred {
+				clientURLs = append(member.ClientURLs, clientURLs...)
+			} else {
 				clientURLs = append(clientURLs, member.ClientURLs...)
 			}
+		}
+	}
 	return clientURLs, memberList, nil
 }
 
@@ -1545,7 +1559,21 @@ func GetAPIServerURLsFromETCD(ctx context.Context, cfg *config.Control) ([]strin
 // GetMembersClientURLs will list through the member lists in etcd and return
 // back a combined list of client urls for each member in the cluster
 func (e *ETCD) GetMembersClientURLs(ctx context.Context) ([]string, error) {
-	return e.client.Endpoints(), nil
+	ctx, cancel := context.WithTimeout(ctx, testTimeout)
+	defer cancel()
+
+	members, err := e.client.MemberList(ctx)
+	if err != nil {
+		return nil, err
+	}
+
+	var clientURLs []string
+	for _, member := range members.Members {
+		if !member.IsLearner {
+			clientURLs = append(clientURLs, member.ClientURLs...)
+		}
+	}
+	return clientURLs, nil
 }
 
 // GetMembersNames will list through the member lists in etcd and return