docker-container: wait for BuildKit before dialing

driver/docker-container/driver.go

@@ -330,12 +330,14 @@ func (d *Driver) wait(ctx context.Context, l progress.SubLogger) error {
 		bufStderr := &bytes.Buffer{}
 		if err := d.run(ctx, []string{"buildctl", "debug", "workers"}, bufStdout, bufStderr); err != nil {
 			if try > 15 {
-				d.copyLogs(context.TODO(), l)
-				if bufStdout.Len() != 0 {
-					l.Log(1, bufStdout.Bytes())
-				}
-				if bufStderr.Len() != 0 {
-					l.Log(2, bufStderr.Bytes())
+				if l != nil {
+					d.copyLogs(context.TODO(), l)
+					if bufStdout.Len() != 0 {
+						l.Log(1, bufStdout.Bytes())
+					}
+					if bufStderr.Len() != 0 {
+						l.Log(2, bufStderr.Bytes())
+					}
 				}
 				return err
 			}
@@ -508,6 +510,11 @@ func (d *Driver) Rm(ctx context.Context, force, rmVolume, rmDaemon bool) error {
 }
 
 func (d *Driver) Dial(ctx context.Context) (net.Conn, error) {
+	// Docker marks the container running before buildkitd has necessarily
+	// bound its socket, so verify readiness before opening dial-stdio.
+	if err := d.wait(ctx, nil); err != nil {
+		return nil, err
+	}
 	_, conn, err := d.exec(ctx, []string{"buildctl", "dial-stdio"})
 	if err != nil {
 		return nil, err

driver/manager.go

@@ -127,17 +127,23 @@ func GetFactories(instanceRequired bool) []Factory {
 type DriverHandle struct {
 	Driver
 	client                  *client.Client
-	err                     error
-	once                    sync.Once
+	clientMu                sync.Mutex
 	historyAPISupportedOnce sync.Once
 	historyAPISupported     bool
 }
 
 func (d *DriverHandle) Client(ctx context.Context, opt ...client.ClientOpt) (*client.Client, error) {
-	d.once.Do(func() {
-		d.client, d.err = d.Driver.Client(ctx, append(d.getClientOptions(), opt...)...)
-	})
-	return d.client, d.err
+	d.clientMu.Lock()
+	defer d.clientMu.Unlock()
+	if d.client != nil {
+		return d.client, nil
+	}
+	c, err := d.Driver.Client(ctx, append(d.getClientOptions(), opt...)...)
+	if err != nil {
+		return nil, err
+	}
+	d.client = c
+	return c, nil
 }
 
 func (d *DriverHandle) UncachedClient(ctx context.Context) (*client.Client, error) {

driver/manager_test.go

@@ -0,0 +1,36 @@
+package driver
+
+import (
+	"context"
+	"testing"
+
+	"github.com/moby/buildkit/client"
+	"github.com/stretchr/testify/require"
+)
+
+func TestBootRetriesClientAfterErrNotRunning(t *testing.T) {
+	d := &retryDriver{client: &client.Client{}}
+
+	c, err := Boot(context.Background(), context.Background(), &DriverHandle{Driver: d}, nil)
+	require.NoError(t, err)
+	require.Same(t, d.client, c)
+	require.Equal(t, 2, d.clientCalls)
+}
+
+type retryDriver struct {
+	Driver
+	client      *client.Client
+	clientCalls int
+}
+
+func (d *retryDriver) Info(context.Context) (*Info, error) {
+	return &Info{Status: Running}, nil
+}
+
+func (d *retryDriver) Client(context.Context, ...client.ClientOpt) (*client.Client, error) {
+	d.clientCalls++
+	if d.clientCalls == 1 {
+		return nil, ErrNotRunning{}
+	}
+	return d.client, nil
+}

tests/build.go

@@ -14,12 +14,14 @@ import (
 	"regexp"
 	"strings"
 	"testing"
+	"time"
 
 	"github.com/containerd/containerd/v2/core/content"
 	"github.com/containerd/containerd/v2/plugins/content/local"
 	"github.com/containerd/continuity/fs/fstest"
 	"github.com/containerd/platforms"
 	"github.com/creack/pty"
+	"github.com/docker/buildx/driver"
 	"github.com/docker/buildx/localstate"
 	"github.com/docker/buildx/util/confutil"
 	"github.com/docker/buildx/util/gitutil"
@@ -42,6 +44,7 @@ import (
 	"github.com/pkg/errors"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
+	"golang.org/x/sync/errgroup"
 )
 
 func buildCmd(sb integration.Sandbox, opts ...cmdOpt) (string, error) {
@@ -94,6 +97,7 @@ var buildTests = []func(t *testing.T, sb integration.Sandbox){
 	testBuildCheckCallOutput,
 	testBuildExtraHosts,
 	testBuildIndexAnnotationsLoadDocker,
+	testBuildDockerContainerConcurrentFirstBuild,
 }
 
 func testBuild(t *testing.T, sb integration.Sandbox) {
@@ -1831,6 +1835,64 @@ func testBuildIndexAnnotationsLoadDocker(t *testing.T, sb integration.Sandbox) {
 	require.Contains(t, out, "index annotations not supported for single platform export")
 }
 
+func testBuildDockerContainerConcurrentFirstBuild(t *testing.T, sb integration.Sandbox) {
+	if !isDockerContainerWorker(sb) {
+		t.Skip("only testing with docker-container worker")
+	}
+	integration.SkipOnPlatform(t, "windows")
+
+	dir := tmpdir(t,
+		fstest.CreateFile("Dockerfile", []byte("FROM scratch\nCOPY marker /marker\n"), 0o600),
+		fstest.CreateFile("marker", []byte("hi"), 0o600),
+	)
+
+	builderName := "concurrent-" + identity.NewID()
+	out, err := createCmd(sb, withArgs(
+		"--name", builderName,
+		"--driver", "docker-container",
+	))
+	require.NoError(t, err, out)
+	t.Cleanup(func() {
+		out, err := rmCmd(sb, withArgs("-f", builderName))
+		require.NoError(t, err, out)
+	})
+
+	var eg errgroup.Group
+	var waited bool
+	defer func() {
+		if !waited {
+			require.NoError(t, eg.Wait())
+		}
+	}()
+	startBuild := func(name string) {
+		eg.Go(func() error {
+			cmd := buildxCmd(sb, withArgs("build", "--progress=quiet", "--output=type=cacheonly", dir))
+			cmd.Env = append(cmd.Env, "BUILDX_BUILDER="+builderName)
+			out, err := cmd.CombinedOutput()
+			if err != nil {
+				return errors.Errorf("%s failed: %v\n%s", name, err, string(out))
+			}
+			return nil
+		})
+	}
+
+	startBuild("bootstrap")
+	containerName := fmt.Sprintf("%s0", driver.BuilderName(builderName))
+	require.EventuallyWithT(t, func(c *assert.CollectT) {
+		cmd := dockerCmd(sb, withArgs("inspect", "-f", "{{.State.Running}}", containerName))
+		out, err := cmd.CombinedOutput()
+		assert.NoError(c, err, string(out))
+		assert.Equal(c, "true", strings.TrimSpace(string(out)))
+	}, 60*time.Second, 20*time.Millisecond, "container %s did not report running", containerName)
+
+	for i := range 5 {
+		startBuild(fmt.Sprintf("sibling %d", i+1))
+	}
+	err = eg.Wait()
+	waited = true
+	require.NoError(t, err)
+}
+
 func createTestProject(t *testing.T) string {
 	dockerfile := []byte(`
 FROM busybox:latest AS base