Add '--sysctl' option to 'network connect'

Equivalent to 'sysctl' in the extended 'run --network' syntax.

Signed-off-by: Rob Murray <rob.murray@docker.com>

Author: robmry

cli/command/network/connect.go

@@ -22,6 +22,7 @@ type connectOptions struct {
 	aliases      []string
 	linklocalips []string
 	driverOpts   []string
+	sysctls      []string
 }
 
 func newConnectCommand(dockerCli command.Cli) *cobra.Command {
@@ -54,13 +55,14 @@ func newConnectCommand(dockerCli command.Cli) *cobra.Command {
 	flags.StringSliceVar(&options.aliases, "alias", []string{}, "Add network-scoped alias for the container")
 	flags.StringSliceVar(&options.linklocalips, "link-local-ip", []string{}, "Add a link-local address for the container")
 	flags.StringSliceVar(&options.driverOpts, "driver-opt", []string{}, "driver options for the network")
+	flags.StringSliceVar(&options.sysctls, "sysctl", []string{}, "short-form interface sysctl: net.X.Y.ethN.Z=V -> X.Y.Z=V")
 	return cmd
 }
 
 func runConnect(ctx context.Context, dockerCli command.Cli, options connectOptions) error {
 	client := dockerCli.Client()
 
-	driverOpts, err := convertDriverOpt(options.driverOpts)
+	driverOpts, err := convertDriverOpt(options.driverOpts, options.sysctls)
 	if err != nil {
 		return err
 	}
@@ -78,7 +80,7 @@ func runConnect(ctx context.Context, dockerCli command.Cli, options connectOptio
 	return client.NetworkConnect(ctx, options.network, options.container, epConfig)
 }
 
-func convertDriverOpt(options []string) (map[string]string, error) {
+func convertDriverOpt(options []string, sysctls []string) (map[string]string, error) {
 	driverOpt := make(map[string]string)
 	for _, opt := range options {
 		k, v, ok := strings.Cut(opt, "=")
@@ -89,5 +91,8 @@ func convertDriverOpt(options []string) (map[string]string, error) {
 		}
 		driverOpt[k] = strings.TrimSpace(v)
 	}
+	if len(sysctls) > 0 {
+		driverOpt[opts.NetlabelEpSysctls] = strings.Join(sysctls, ",")
+	}
 	return driverOpt, nil
 }

cli/command/network/connect_test.go

@@ -6,6 +6,7 @@ import (
 	"testing"
 
 	"github.com/docker/cli/internal/test"
+	"github.com/docker/cli/opts"
 	"github.com/docker/docker/api/types/network"
 	"github.com/pkg/errors"
 	"gotest.tools/v3/assert"
@@ -52,7 +53,8 @@ func TestNetworkConnectWithFlags(t *testing.T) {
 		Links:   []string{"otherctr"},
 		Aliases: []string{"poor-yorick"},
 		DriverOpts: map[string]string{
-			"adriveropt": "anoptval",
+			"adriveropt":           "anoptval",
+			opts.NetlabelEpSysctls: "ipv6.conf.accept_ra=2,ipv6.conf.forwarding=1",
 		},
 	}
 	cli := test.NewFakeCli(&fakeClient{
@@ -72,6 +74,8 @@ func TestNetworkConnectWithFlags(t *testing.T) {
 		{"ip6", "fdef:f401:8da0:1234::5678"},
 		{"link", "otherctr"},
 		{"link-local-ip", "169.254.42.42"},
+		{"sysctl", "ipv6.conf.accept_ra=2"},
+		{"sysctl", "ipv6.conf.forwarding=1"},
 	} {
 		err := cmd.Flags().Set(opt.name, opt.value)
 		assert.Check(t, err)

docs/reference/commandline/network_connect.md

@@ -5,14 +5,15 @@ Connect a container to a network
 
 ### Options
 
-| Name                | Type          | Default | Description                                |
-|:--------------------|:--------------|:--------|:-------------------------------------------|
-| [`--alias`](#alias) | `stringSlice` |         | Add network-scoped alias for the container |
-| `--driver-opt`      | `stringSlice` |         | driver options for the network             |
-| [`--ip`](#ip)       | `string`      |         | IPv4 address (e.g., `172.30.100.104`)      |
-| `--ip6`             | `string`      |         | IPv6 address (e.g., `2001:db8::33`)        |
-| [`--link`](#link)   | `list`        |         | Add link to another container              |
-| `--link-local-ip`   | `stringSlice` |         | Add a link-local address for the container |
+| Name                  | Type          | Default | Description                                              |
+|:----------------------|:--------------|:--------|:---------------------------------------------------------|
+| [`--alias`](#alias)   | `stringSlice` |         | Add network-scoped alias for the container               |
+| `--driver-opt`        | `stringSlice` |         | driver options for the network                           |
+| [`--ip`](#ip)         | `string`      |         | IPv4 address (e.g., `172.30.100.104`)                    |
+| `--ip6`               | `string`      |         | IPv6 address (e.g., `2001:db8::33`)                      |
+| [`--link`](#link)     | `list`        |         | Add link to another container                            |
+| `--link-local-ip`     | `stringSlice` |         | Add a link-local address for the container               |
+| [`--sysctl`](#sysctl) | `stringSlice` |         | short-form interface sysctl: net.X.Y.ethN.Z=V -> X.Y.Z=V |
 
 
 <!---MARKER_GEN_END-->
@@ -23,6 +24,14 @@ Connects a container to a network. You can connect a container by name
 or by ID. Once connected, the container can communicate with other containers in
 the same network.
 
+The `--sysctl` option in `network connect` is restricted to sysctls that start with
+`net.ipv4.` and `net.ipv6.`. The `net.` prefix and the name of the interface must
+not be included. Internally, the sysctl options are added to `DriverOpts` with the
+key `com.docker.network.endpoint.sysctls`, which is where you'll find them in
+`docker inspect` output. Network drivers may restrict the sysctl settings that can
+be modified and, to protect the operation of the network, new restrictions may be
+added in the future.
+
 ## Examples
 
 ### Connect a running container to a network
@@ -64,6 +73,19 @@ being connected to.
 ```console
 $ docker network connect --alias db --alias mysql multi-host-network container2
 ```
+### <a name="sysctl"></a> Set a sysctl for a container's interface (--sysctl)
+
+`--sysctl` sets a network sysctl on the interface created to connect to the
+network, only `net.ipv4.` and `net.ipv6.` settings can be modified. The
+interface name is assigned automatically, so it must be left out along with
+the `net.` prefix.
+
+If the network interface created in the container is called `eth3`, this
+example is equivalent to `net.ipv4.conf.eth3.log_martians=1`.
+
+```console
+$ docker network connect --sysctl ipv4.conf.log_martians=1 multi-host-network container2
+```
 
 ### Network implications of stopping, pausing, or restarting containers