fix: apply the daemon's mtu to job networks (#1270)

Copy the `mtu` of Docker's default bridge network to job networks, since Docker applies the daemon's `mtu` setting only to the default bridge. Docker's default of 1500 is not copied, so `default-network-opts` in the daemon config keeps applying.

Closes https://gitea.com/gitea/runner/issues/232

---------

Co-authored-by: silverwind <2021+silverwind@noreply.gitea.com>
Co-authored-by: silverwind <me@silverwind.io>
Reviewed-on: https://gitea.com/gitea/runner/pulls/1270
Reviewed-by: silverwind <2021+silverwind@noreply.gitea.com>
Co-authored-by: bircni <bircni@icloud.com>

act/container/docker_network.go

@@ -87,45 +87,54 @@ func NewDockerNetworkCreateExecutor(name string, opts NewDockerNetworkCreateExec
 			return err
 		}
 		defer cli.Close()
+		return createDockerNetwork(ctx, cli, name, opts)
+	}
+}
 
-		// Only create the network if it doesn't exist
-		networks, err := cli.NetworkList(ctx, client.NetworkListOptions{})
-		if err != nil {
+func createDockerNetwork(ctx context.Context, cli client.APIClient, name string, opts NewDockerNetworkCreateExecutorInput) error {
+	// Only create the network if it doesn't exist
+	networks, err := cli.NetworkList(ctx, client.NetworkListOptions{})
+	if err != nil {
+		return err
+	}
+	var options map[string]string
+	// For Gitea, reduce log noise
+	// common.Logger(ctx).Debugf("%v", networks)
+	for _, n := range networks.Items {
+		if n.Name == name {
+			common.Logger(ctx).Debugf("Network %v exists", name)
+			return nil
+		}
+		// the daemon's mtu only reaches its default bridge, Docker's default is left out to keep default-network-opts
+		if mtu := n.Options["com.docker.network.driver.mtu"]; n.Name == network.NetworkBridge && mtu != "" && mtu != "1500" {
+			options = map[string]string{"com.docker.network.driver.mtu": mtu}
+		}
+	}
+
+	for i := range networkCreateAttempts {
+		if i > 0 {
+			common.Logger(ctx).Infof("Waiting for a free docker address pool to create network %s", name)
+			select {
+			case <-ctx.Done():
+				return ctx.Err()
+			case <-time.After(time.Duration(i) * networkCreateRetryDelay):
+			}
+		}
+		if _, err = cli.NetworkCreate(ctx, name, client.NetworkCreateOptions{
+			Driver:     "bridge",
+			Scope:      "local",
+			EnableIPv4: opts.EnableIPv4,
+			EnableIPv6: opts.EnableIPv6,
+			Options:    options,
+			Labels:     runnerLabels(opts.RunnerUUID),
+		}); err == nil {
+			return nil
+		}
+		if !isAddressPoolExhausted(err) {
 			return err
 		}
-		// For Gitea, reduce log noise
-		// common.Logger(ctx).Debugf("%v", networks)
-		for _, n := range networks.Items {
-			if n.Name == name {
-				common.Logger(ctx).Debugf("Network %v exists", name)
-				return nil
-			}
-		}
-
-		for i := range networkCreateAttempts {
-			if i > 0 {
-				common.Logger(ctx).Infof("Waiting for a free docker address pool to create network %s", name)
-				select {
-				case <-ctx.Done():
-					return ctx.Err()
-				case <-time.After(time.Duration(i) * networkCreateRetryDelay):
-				}
-			}
-			if _, err = cli.NetworkCreate(ctx, name, client.NetworkCreateOptions{
-				Driver:     "bridge",
-				Scope:      "local",
-				EnableIPv4: opts.EnableIPv4,
-				EnableIPv6: opts.EnableIPv6,
-				Labels:     runnerLabels(opts.RunnerUUID),
-			}); err == nil {
-				return nil
-			}
-			if !isAddressPoolExhausted(err) {
-				return err
-			}
-		}
-		return fmt.Errorf("docker has no address pool left for this job's network, lower runner.capacity or widen default-address-pools in the docker daemon config: %w", err)
 	}
+	return fmt.Errorf("docker has no address pool left for this job's network, lower runner.capacity or widen default-address-pools in the docker daemon config: %w", err)
 }
 
 func runnerLabels(runnerUUID string) map[string]string {

act/container/docker_network_test.go

@@ -57,6 +57,27 @@ func TestIsAddressPoolExhausted(t *testing.T) {
 	assert.False(t, isAddressPoolExhausted(cerrdefs.ErrInvalidArgument.WithMessage("invalid subnet 10.0.0.0/8: it overlaps with an existing network")))
 }
 
+func TestCreateDockerNetworkInheritsDaemonMTU(t *testing.T) {
+	ctx := context.Background()
+	for _, tc := range []struct {
+		bridgeOptions, want map[string]string
+	}{
+		{
+			map[string]string{"com.docker.network.bridge.host_binding_ipv4": "127.0.0.1", "com.docker.network.driver.mtu": "1450"},
+			map[string]string{"com.docker.network.driver.mtu": "1450"},
+		},
+		{map[string]string{"com.docker.network.driver.mtu": "1500"}, nil},
+	} {
+		client := &mockDockerClient{}
+		client.On("NetworkList", ctx, mobyclient.NetworkListOptions{}).
+			Return(mobyclient.NetworkListResult{Items: []network.Summary{{Name: network.NetworkBridge, Options: tc.bridgeOptions}}}, nil)
+		client.On("NetworkCreate", ctx, "job-network", mobyclient.NetworkCreateOptions{Driver: "bridge", Scope: "local", Options: tc.want}).
+			Return(mobyclient.NetworkCreateResult{}, nil)
+		require.NoError(t, createDockerNetwork(ctx, client, "job-network", NewDockerNetworkCreateExecutorInput{}))
+		client.AssertExpectations(t)
+	}
+}
+
 func (m *mockDockerClient) NetworkConnect(ctx context.Context, id string, opts mobyclient.NetworkConnectOptions) (mobyclient.NetworkConnectResult, error) {
 	return mobyclient.NetworkConnectResult{}, m.Called(ctx, id, opts).Error(0)
 }

act/container/docker_run_test.go

@@ -137,6 +137,11 @@ func (m *mockDockerClient) NetworkList(ctx context.Context, opts mobyclient.Netw
 	return args.Get(0).(mobyclient.NetworkListResult), args.Error(1)
 }
 
+func (m *mockDockerClient) NetworkCreate(ctx context.Context, name string, opts mobyclient.NetworkCreateOptions) (mobyclient.NetworkCreateResult, error) {
+	args := m.Called(ctx, name, opts)
+	return args.Get(0).(mobyclient.NetworkCreateResult), args.Error(1)
+}
+
 func (m *mockDockerClient) NetworkInspect(ctx context.Context, id string, opts mobyclient.NetworkInspectOptions) (mobyclient.NetworkInspectResult, error) {
 	args := m.Called(ctx, id, opts)
 	return args.Get(0).(mobyclient.NetworkInspectResult), args.Error(1)

internal/pkg/config/config.example.yaml

@@ -223,6 +223,7 @@ container:
   # created by the runner. Omit the entire block to use Docker's defaults. An auto-created
   # network is labelled com.gitea.runner.uuid=<this runner's uuid>, which is how the idle
   # cleanup tells its own leftovers apart from those of other runners on the same daemon.
+  # It also takes the `mtu` set in the Docker daemon config.
   #network_create_options:
   #  enable_ipv4: true # Omit to use Docker's default (IPv4 enabled). Set false to disable IPv4.
   #  enable_ipv6: false # Omit to use Docker's default (IPv6 disabled). Enabling it requires dockerd started with --ipv6.