Fix Docker API compatibility with network alias (#17167)

* Add BaseHostsFile to container configuration
* Do not copy /etc/hosts file from host when creating a container using Docker API

Signed-off-by: Gavin Lam <gavin.oss@tutamail.com>

libpod/container_config.go

@@ -291,6 +291,12 @@ type ContainerNetworkConfig struct {
 	// bind-mounted inside the container.
 	// Conflicts with HostAdd.
 	UseImageHosts bool
+	// BaseHostsFile is the path to a hosts file, the entries from this file
+	// are added to the containers hosts file. As special value "image" is
+	// allowed which uses the /etc/hosts file from within the image and "none"
+	// which uses no base file at all. If it is empty we should default
+	// to the base_hosts_file configuration in containers.conf.
+	BaseHostsFile string `json:"baseHostsFile,omitempty"`
 	// Hosts to add in container
 	// Will be appended to host's host file
 	HostAdd []string `json:"hostsAdd,omitempty"`

libpod/container_internal_common.go

@@ -2267,7 +2267,14 @@ func (c *Container) addHosts() error {
 	if err != nil {
 		return fmt.Errorf("failed to get container ip host entries: %w", err)
 	}
-	baseHostFile, err := etchosts.GetBaseHostFile(c.runtime.config.Containers.BaseHostsFile, c.state.Mountpoint)
+
+	// Consider container level BaseHostsFile configuration first.
+	// If it is empty, fallback to containers.conf level configuration.
+	baseHostsFileConf := c.config.BaseHostsFile
+	if baseHostsFileConf == "" {
+		baseHostsFileConf = c.runtime.config.Containers.BaseHostsFile
+	}
+	baseHostFile, err := etchosts.GetBaseHostFile(baseHostsFileConf, c.state.Mountpoint)
 	if err != nil {
 		return err
 	}

libpod/options.go

@@ -2373,6 +2373,19 @@ func WithGroupEntry(groupEntry string) CtrCreateOption {
 	}
 }
 
+// WithBaseHostsFile sets the option to copy /etc/hosts file.
+func WithBaseHostsFile(baseHostsFile string) CtrCreateOption {
+	return func(ctr *Container) error {
+		if ctr.valid {
+			return define.ErrCtrFinalized
+		}
+
+		ctr.config.BaseHostsFile = baseHostsFile
+
+		return nil
+	}
+}
+
 // WithMountAllDevices sets the option to mount all of a privileged container's
 // host devices
 func WithMountAllDevices() CtrCreateOption {

pkg/api/handlers/compat/containers_create.go

@@ -116,6 +116,8 @@ func CreateContainer(w http.ResponseWriter, r *http.Request) {
 	}
 	// moby always create the working directory
 	sg.CreateWorkingDir = true
+	// moby doesn't inherit /etc/hosts from host
+	sg.BaseHostsFile = "none"
 
 	ic := abi.ContainerEngine{Libpod: runtime}
 	report, err := ic.ContainerCreate(r.Context(), sg)

pkg/specgen/generate/container_create.go

@@ -378,6 +378,9 @@ func createContainerOptions(rt *libpod.Runtime, s *specgen.SpecGenerator, pod *l
 	if s.GroupEntry != "" {
 		options = append(options, libpod.WithGroupEntry(s.GroupEntry))
 	}
+	if s.BaseHostsFile != "" {
+		options = append(options, libpod.WithBaseHostsFile(s.BaseHostsFile))
+	}
 
 	if s.Privileged {
 		options = append(options, libpod.WithMountAllDevices())

pkg/specgen/specgen.go

@@ -507,6 +507,13 @@ type ContainerNetworkConfig struct {
 	// specgen is stable so we can not change this right now.
 	// TODO (5.0): change to pointer
 	UseImageHosts bool `json:"use_image_hosts"`
+	// BaseHostsFile is the path to a hosts file, the entries from this file
+	// are added to the containers hosts file. As special value "image" is
+	// allowed which uses the /etc/hosts file from within the image and "none"
+	// which uses no base file at all. If it is empty we should default
+	// to the base_hosts_file configuration in containers.conf.
+	// Optional.
+	BaseHostsFile string `json:"base_hosts_file,omitempty"`
 	// HostAdd is a set of hosts which will be added to the container's
 	// /etc/hosts file.
 	// Conflicts with UseImageHosts.

test/compose/etc_hosts/README.md

@@ -0,0 +1,10 @@
+etc hosts
+===========
+
+This test mounts a /etc/hosts file in the host containing an entry `foobar`, then create a container with an alias of the same hostname.
+
+Validation
+------------
+
+* No /etc/hosts entries are copied from the host. There should be only one entry of the hostname, which is IP address of the alias.
+* The hostname is resolved to IP address of the alias.

test/compose/etc_hosts/docker-compose.yml

@@ -0,0 +1,19 @@
+version: '3.3'
+
+services:
+  test:
+    image: alpine
+    command: ["top"]
+    hostname: foobar
+    networks:
+      net1:
+        aliases:
+          - foobar
+
+networks:
+  net1:
+    driver: bridge
+    ipam:
+      driver: default
+      config:
+        - subnet: 10.123.0.0/24

test/compose/etc_hosts/hosts

@@ -0,0 +1,2 @@
+127.0.0.1 localhost
+127.0.0.1 foobar

test/compose/etc_hosts/setup.sh

@@ -0,0 +1,5 @@
+if ! is_rootless; then
+    mount --bind $TEST_ROOTDIR/etc_hosts/hosts /etc/hosts
+else
+    $PODMAN_BIN unshare mount --bind $TEST_ROOTDIR/etc_hosts/hosts /etc/hosts
+fi

test/compose/etc_hosts/teardown.sh

@@ -0,0 +1,5 @@
+if ! is_rootless; then
+    umount /etc/hosts
+else
+    $PODMAN_BIN unshare umount /etc/hosts
+fi

test/compose/etc_hosts/tests.sh

@@ -0,0 +1,12 @@
+# -*- bash -*-
+
+ctr_name="etc_hosts_test_1"
+if [ "$TEST_FLAVOR" = "compose_v2" ]; then
+    ctr_name="etc_hosts-test-1"
+fi
+
+podman exec "$ctr_name" sh -c 'grep "foobar" /etc/hosts'
+like "$output" "10\.123\.0\." "$testname : no entries are copied from the host"
+
+podman exec "$ctr_name" sh -c 'getent hosts foobar | awk "{print \$1}"'
+like "$output" "10\.123\.0\." "$testname : hostname is resolved to IP address of the alias"