allow teleport to start when some etcd nodes are unreachable

lib/backend/etcdbk/etcd.go

@@ -28,6 +28,7 @@ import (
 	"sort"
 	"strconv"
 	"strings"
+	"sync"
 	"time"
 
 	"github.com/coreos/go-semver/semver"
@@ -265,6 +266,7 @@ func New(ctx context.Context, params backend.Params, opts ...Option) (*EtcdBacke
 		CleanupInterval: utils.SeventhJitter(time.Minute * 2),
 	})
 	if err != nil {
+		cancel()
 		return nil, trace.Wrap(err)
 	}
 
@@ -285,28 +287,19 @@ func New(ctx context.Context, params backend.Params, opts ...Option) (*EtcdBacke
 	}
 
 	// Check that the etcd nodes are at least the minimum version supported
-	if err = b.reconnect(ctx); err != nil {
+	if err = b.reconnect(b.ctx); err != nil {
+		b.Close()
 		return nil, trace.Wrap(err)
 	}
-	timeout, cancel := context.WithTimeout(ctx, time.Second*3*time.Duration(len(cfg.Nodes)))
-	defer cancel()
-	for _, n := range cfg.Nodes {
-		status, err := b.clients.Next().Status(timeout, n)
-		if err != nil {
-			return nil, trace.Wrap(err)
-		}
-
-		ver := semver.New(status.Version)
-		min := semver.New(teleport.MinimumEtcdVersion)
-		if ver.LessThan(*min) {
-			return nil, trace.BadParameter("unsupported version of etcd %v for node %v, must be %v or greater",
-				status.Version, n, teleport.MinimumEtcdVersion)
-		}
+	if err := b.checkVersion(b.ctx); err != nil {
+		b.Close()
+		return nil, trace.Wrap(err)
 	}
 
 	// Reconnect the etcd client to work around a data race in their code.
 	// Upstream fix: https://github.com/etcd-io/etcd/pull/12992
-	if err = b.reconnect(ctx); err != nil {
+	if err = b.reconnect(b.ctx); err != nil {
+		b.Close()
 		return nil, trace.Wrap(err)
 	}
 	go b.asyncWatch()
@@ -315,6 +308,57 @@ func New(ctx context.Context, params backend.Params, opts ...Option) (*EtcdBacke
 	return b, nil
 }
 
+func (b *EtcdBackend) checkVersion(ctx context.Context) error {
+	// scope version check to one third the default I/O timeout since slowness that is
+	// anywhere near the default timeout is going to cause systemic issues.
+	ctx, cancel := context.WithTimeout(ctx, apidefaults.DefaultIOTimeout/3)
+
+	results := make(chan error, len(b.cfg.Nodes))
+
+	var wg sync.WaitGroup
+	for _, nn := range b.cfg.Nodes {
+		wg.Add(1)
+		go func(n string) (err error) {
+			defer func() {
+				results <- err
+				wg.Done()
+			}()
+			status, err := b.clients.Next().Status(ctx, n)
+			if err != nil {
+				return trace.Wrap(err)
+			}
+
+			ver, err := semver.NewVersion(status.Version)
+			if err != nil {
+				return trace.BadParameter("failed to parse etcd version %q: %v", status.Version, err)
+			}
+
+			min := semver.New(teleport.MinimumEtcdVersion)
+			if ver.LessThan(*min) {
+				return trace.BadParameter("unsupported version of etcd %v for node %v, must be %v or greater",
+					status.Version, n, teleport.MinimumEtcdVersion)
+			}
+
+			return nil
+		}(nn)
+	}
+
+	// wait for results
+	var err error
+	for range b.cfg.Nodes {
+		err = <-results
+		if err == nil {
+			// stop on first success, we don't care about all endpoints
+			// being healthy, just that at least one is.
+			break
+		}
+	}
+
+	cancel()
+	wg.Wait()
+	return trace.Wrap(err)
+}
+
 // Validate checks if all the parameters are present/valid
 func (cfg *Config) Validate() error {
 	if len(cfg.Key) == 0 {