Merge pull request #39204 from olljanat/fix-hostname-dns-resolution

Add alias for hostname if hostname != container name

daemon/container_operations.go

@@ -674,6 +674,18 @@ func (daemon *Daemon) updateNetworkConfig(container *container.Container, n libn
 		if addShortID {
 			endpointConfig.Aliases = append(endpointConfig.Aliases, shortID)
 		}
+		if container.Name != container.Config.Hostname {
+			addHostname := true
+			for _, alias := range endpointConfig.Aliases {
+				if alias == container.Config.Hostname {
+					addHostname = false
+					break
+				}
+			}
+			if addHostname {
+				endpointConfig.Aliases = append(endpointConfig.Aliases, container.Config.Hostname)
+			}
+		}
 	}
 
 	if err := validateNetworkingConfig(n, endpointConfig); err != nil {

integration/container/run_linux_test.go

@@ -10,6 +10,7 @@ import (
 	containertypes "github.com/docker/docker/api/types/container"
 	"github.com/docker/docker/api/types/versions"
 	"github.com/docker/docker/integration/internal/container"
+	net "github.com/docker/docker/integration/internal/network"
 	"gotest.tools/assert"
 	is "gotest.tools/assert/cmp"
 	"gotest.tools/poll"
@@ -93,3 +94,37 @@ func TestNISDomainname(t *testing.T) {
 	assert.Equal(t, 0, res.ExitCode)
 	assert.Check(t, is.Equal(domainname, strings.TrimSpace(res.Stdout())))
 }
+
+func TestHostnameDnsResolution(t *testing.T) {
+	skip.If(t, testEnv.DaemonInfo.OSType != "linux")
+
+	defer setupTest(t)()
+	client := testEnv.APIClient()
+	ctx := context.Background()
+
+	const (
+		hostname = "foobar"
+	)
+
+	// using user defined network as we want to use internal DNS
+	netName := "foobar-net"
+	net.CreateNoError(t, context.Background(), client, netName, net.WithDriver("bridge"))
+
+	cID := container.Run(t, ctx, client, func(c *container.TestContainerConfig) {
+		c.Config.Hostname = hostname
+		c.HostConfig.NetworkMode = containertypes.NetworkMode(netName)
+	})
+
+	poll.WaitOn(t, container.IsInState(ctx, client, cID, "running"), poll.WithDelay(100*time.Millisecond))
+
+	inspect, err := client.ContainerInspect(ctx, cID)
+	assert.NilError(t, err)
+	assert.Check(t, is.Equal(hostname, inspect.Config.Hostname))
+
+	// Clear hosts file so ping will use DNS for hostname resolution
+	res, err := container.Exec(ctx, client, cID,
+		[]string{"sh", "-c", "echo 127.0.0.1 localhost | tee /etc/hosts && ping -c 1 foobar"})
+	assert.NilError(t, err)
+	assert.Check(t, is.Equal("", res.Stderr()))
+	assert.Equal(t, 0, res.ExitCode)
+}