Add options to LXC builder for influencing for how containers are built and started

via

- create_options: a list of options passed to lxc-create
- start_options: a list of options passed to lxc-start
- attach_options: a list of options passed to lxc-attach

Also extended existing LXC builder BATS tests to exercise the new builder
options, and added website docs.

builder/lxc/communicator.go

@@ -16,6 +16,7 @@ import (
 type LxcAttachCommunicator struct {
 	RootFs        string
 	ContainerName string
+	AttachOptions []string
 	CmdWrapper    CommandWrapper
 }
 
@@ -110,8 +111,13 @@ func (c *LxcAttachCommunicator) DownloadDir(src string, dst string, exclude []st
 
 func (c *LxcAttachCommunicator) Execute(commandString string) (*exec.Cmd, error) {
 	log.Printf("Executing with lxc-attach in container: %s %s %s", c.ContainerName, c.RootFs, commandString)
+
+	attachCommand := []string{"sudo", "lxc-attach"}
+	attachCommand = append(attachCommand, c.AttachOptions...)
+	attachCommand = append(attachCommand, []string{"--name", "%s", "--", "/bin/sh -c \"%s\""}...)
+
 	command, err := c.CmdWrapper(
-		fmt.Sprintf("sudo lxc-attach --name %s -- /bin/sh -c \"%s\"", c.ContainerName, commandString))
+		fmt.Sprintf(strings.Join(attachCommand, " "), c.ContainerName, commandString))
 	if err != nil {
 		return nil, err
 	}

builder/lxc/config.go

@@ -18,6 +18,9 @@ type Config struct {
 	ContainerName       string   `mapstructure:"container_name"`
 	CommandWrapper      string   `mapstructure:"command_wrapper"`
 	RawInitTimeout      string   `mapstructure:"init_timeout"`
+	CreateOptions       []string `mapstructure:"create_options"`
+	StartOptions        []string `mapstructure:"start_options"`
+	AttachOptions       []string `mapstructure:"attach_options"`
 	Name                string   `mapstructure:"template_name"`
 	Parameters          []string `mapstructure:"template_parameters"`
 	EnvVars             []string `mapstructure:"template_environment_vars"`

builder/lxc/step_lxc_create.go

@@ -28,12 +28,15 @@ func (s *stepLxcCreate) Run(state multistep.StateBag) multistep.StepAction {
 	}
 
 	commands := make([][]string, 3)
-	commands[0] = append(config.EnvVars, []string{"lxc-create", "-n", name, "-t", config.Name, "--"}...)
+	commands[0] = append(config.EnvVars, "lxc-create")
+	commands[0] = append(commands[0], config.CreateOptions...)
+	commands[0] = append(commands[0], []string{"-n", name, "-t", config.Name, "--"}...)
 	commands[0] = append(commands[0], config.Parameters...)
 	// prevent tmp from being cleaned on boot, we put provisioning scripts there
 	// todo: wait for init to finish before moving on to provisioning instead of this
 	commands[1] = []string{"touch", filepath.Join(rootfs, "tmp", ".tmpfs")}
-	commands[2] = []string{"lxc-start", "-d", "--name", name}
+	commands[2] = append([]string{"lxc-start"}, config.StartOptions...)
+	commands[2] = append(commands[2], []string{"-d", "--name", name}...)
 
 	ui.Say("Creating container...")
 	for _, command := range commands {

builder/lxc/step_provision.go

@@ -19,6 +19,7 @@ func (s *StepProvision) Run(state multistep.StateBag) multistep.StepAction {
 	// Create our communicator
 	comm := &LxcAttachCommunicator{
 		ContainerName: config.ContainerName,
+		AttachOptions: config.AttachOptions,
 		RootFs:        mountPath,
 		CmdWrapper:    wrappedCommand,
 	}

builder/lxc/step_wait_init.go

@@ -76,6 +76,7 @@ func (s *StepWaitInit) waitForInit(state multistep.StateBag, cancel <-chan struc
 
 		comm := &LxcAttachCommunicator{
 			ContainerName: config.ContainerName,
+			AttachOptions: config.AttachOptions,
 			RootFs:        mountPath,
 			CmdWrapper:    wrappedCommand,
 		}

test/builder_lxc.bats

@@ -1,40 +1,106 @@
 #!/usr/bin/env bats
 #
-# This tests the lxc builder. The teardown function will
+# This tests the lxc builder by creating minimal containers and checking that
-# delete any images in the output-lxc-* folders.
+# custom lxc container configuration files are successfully applied. The
+# teardown function will delete any images in the output-lxc-* folders along
+# with the auto-generated lxc container configuration files and hook scripts.
 
 #load test_helper
 #fixtures builder-lxc
 FIXTURE_ROOT="$BATS_TEST_DIRNAME/fixtures/builder-lxc"
 
+have_command() {
+    command -v "$1" >/dev/null 2>&1
+}
+
 # Required parameters
-command -v lxc-create >/dev/null 2>&1 || {
+have_command lxc-create || {
     echo "'lxc-create' must be installed via the lxc (or lxc1 for ubuntu >=16.04) package" >&2
     exit 1
 }
 
+DESTROY_HOOK_SCRIPT=$FIXTURE_ROOT/destroy-hook.sh
+DESTROY_HOOK_LOG=$FIXTURE_ROOT/destroy-hook.log
+printf > "$DESTROY_HOOK_SCRIPT" '
+echo "$LXC_NAME" > "%s"
+' "$DESTROY_HOOK_LOG"
+chmod +x "$DESTROY_HOOK_SCRIPT"
+
+INIT_CONFIG=$FIXTURE_ROOT/lxc.custom.conf
+printf > "$INIT_CONFIG" '
+lxc.hook.destroy = %s
+' "$DESTROY_HOOK_SCRIPT"
+
 teardown() {
+    for f in "$INIT_CONFIG" "$DESTROY_HOOK_SCRIPT" "$DESTROY_HOOK_LOG"; do
+        [ -e "$f" ] && rm -f "$f"
+    done
+
     rm -rf output-lxc-*
 }
 
-@test "lxc: build centos minimal.json" {
+assert_build() {
-    run packer build -var template_name=centos  $FIXTURE_ROOT/minimal.json
+    local template_name="$1"
-    [ "$status" -eq 0 ]
+    shift
-    [ -f output-lxc-centos/rootfs.tar.gz ]
+
-    [ -f output-lxc-centos/lxc-config ]
+    local build_status=0
+
+    run packer build -var template_name="$template_name"  "$@"
+
+    [ "$status" -eq 0 ] || {
+        echo "${template_name} build exited badly: $status" >&2
+        echo "$output" >&2
+        build_status="$status"
+    }
+
+    for expected in "output-lxc-${template_name}"/{rootfs.tar.gz,lxc-config}; do
+        [ -f "$expected" ] || {
+            echo "missing expected artifact '${expected}'" >&2
+            build_status=1
+        }
+    done
+
+    return $build_status
 }
 
+assert_container_name() {
+    local container_name="$1"
+
+    [ -f "$DESTROY_HOOK_LOG" ] || {
+        echo "missing expected lxc.hook.destroy logfile '$DESTROY_HOOK_LOG'"
+        return 1
+    }
+
+    read -r lxc_name < "$DESTROY_HOOK_LOG"
+
+    [ "$lxc_name" = "$container_name" ]
+}
+
+@test "lxc: build centos minimal.json" {
+    have_command yum || skip "'yum' must be installed to build centos containers"
+    local container_name=packer-lxc-centos
+    assert_build centos -var init_config="$INIT_CONFIG" \
+        -var container_name="$container_name" \
+        $FIXTURE_ROOT/minimal.json
+    assert_container_name "$container_name"
+}
 
 @test "lxc: build trusty minimal.json" {
-    run packer build -var template_name=ubuntu -var template_parameters="SUITE=trusty" $FIXTURE_ROOT/minimal.json
+    have_command debootstrap || skip "'debootstrap' must be installed to build ubuntu containers"
-    [ "$status" -eq 0 ]
+    local container_name=packer-lxc-ubuntu
-    [ -f output-lxc-ubuntu/rootfs.tar.gz ]
+    assert_build ubuntu -var init_config="$INIT_CONFIG" \
-    [ -f output-lxc-ubuntu/lxc-config ]
+        -var container_name="$container_name" \
+        -var template_parameters="SUITE=trusty" \
+        $FIXTURE_ROOT/minimal.json
+    assert_container_name "$container_name"
 }
 
 @test "lxc: build debian minimal.json" {
-    run packer build -var template_name=debian -var template_parameters="SUITE=jessie" $FIXTURE_ROOT/minimal.json
+    have_command debootstrap || skip "'debootstrap' must be installed to build debian containers"
-    [ "$status" -eq 0 ]
+    local container_name=packer-lxc-debian
-    [ -f output-lxc-debian/rootfs.tar.gz ]
+    assert_build debian -var init_config="$INIT_CONFIG" \
-    [ -f output-lxc-debian/lxc-config ]
+        -var container_name="$container_name" \
+        -var template_parameters="SUITE=jessie" \
+        $FIXTURE_ROOT/minimal.json
+    assert_container_name "$container_name"
 }

test/fixtures/builder-lxc/minimal.json

@@ -1,13 +1,29 @@
 {
   "variables": {
     "template_name": "debian",
-    "template_parameters": "SUITE=jessie"
+    "template_parameters": "SUITE=jessie",
+    "container_name": "packer-lxc",
+    "set_var": "hello"
   },
+  "provisioners": [
+    {
+      "type": "shell",
+      "inline": [
+        "if [ \"$SET_VAR\" != \"{{user `set_var`}}\" ]; then",
+        "   echo \"Got unexpected value '$SET_VAR' for SET_VAR\" 1>&2",
+        "   exit 1",
+        "fi"
+      ]
+    }
+  ],
   "builders": [
     {
       "type": "lxc",
       "name": "lxc-{{user `template_name`}}",
       "template_name": "{{user `template_name`}}",
+      "container_name": "{{user `container_name`}}",
+      "create_options": [ "-f", "{{user `init_config`}}" ],
+      "attach_options": [ "--clear-env", "--set-var", "SET_VAR={{user `set_var`}}" ],
       "config_file": "/usr/share/lxc/config/{{user `template_name`}}.common.conf",
       "template_environment_vars": [ "{{user `template_parameters`}}" ]
     }

website/source/docs/builders/lxc.html.md

@@ -110,3 +110,18 @@ Below is a fully functioning example.
    `/usr/share/lxc/templates/lxc-<template_name>`. Note: This gets passed as
    ARGV to the template command. Ensure you have an array of strings, as
    a single string with spaces probably won't work. Defaults to `[]`.
+
+-  `create_options` (array of strings) - Options to pass to `lxc-create`. For
+   instance, you can specify a custom LXC container configuration file with
+   `["-f", "/path/to/lxc.conf"]`. Defaults to `[]`. See `man 1 lxc-create` for
+   available options.
+
+-  `start_options` (array of strings) - Options to pass to `lxc-start`. For
+   instance, you can override parameters from the LXC container configuration
+   file via `["--define", "KEY=VALUE"]`. Defaults to `[]`. See `man 1
+   lxc-start` for available options.
+
+-  `attach_options` (array of strings) - Options to pass to `lxc-attach`. For
+   instance, you can prevent the container from inheriting the host machine's
+   environment by specifying `["--clear-env"]`. Defaults to `[]`. See `man 1
+   lxc-attach` for available options.