implement init containers in podman

this is the first pass at implementing init containers for podman pods.
init containersare made popular by k8s as a way to run setup for pods
before the pods standard containers run.

unlike k8s, we support two styles of init containers: always and
oneshot.  always means the container stays in the pod and starts
whenever a pod is started.  this does not apply to pods restarting.
oneshot means the container runs onetime when the pod starts and then is
removed.

Signed-off-by: Brent Baude <bbaude@redhat.com>

3 files changed, 26 insertions, 1 deletions

diff --git a/cmd/podman/common/create_opts.go b/cmd/podman/common/create_opts.go
index 42e0efe5d..61f08b73b 100644
--- a/cmd/podman/common/create_opts.go
+++ b/cmd/podman/common/create_opts.go
@@ -61,6 +61,7 @@ type ContainerCLIOpts struct {
 	HTTPProxy         bool
 	ImageVolume       string
 	Init              bool
+	InitContainerType string
 	InitPath          string
 	Interactive       bool
 	IPC               string
diff --git a/cmd/podman/common/specgen.go b/cmd/podman/common/specgen.go
index 42f515ace..118091855 100644
--- a/cmd/podman/common/specgen.go
+++ b/cmd/podman/common/specgen.go
@@ -659,6 +659,8 @@ func FillOutSpecGen(s *specgen.SpecGenerator, c *ContainerCLIOpts, args []string
 	s.PidFile = c.PidFile
 	s.Volatile = c.Rm
 
+	// Initcontainers
+	s.InitContainerType = c.InitContainerType
 	return nil
 }
 
diff --git a/cmd/podman/containers/create.go b/cmd/podman/containers/create.go
index c63c074f7..895736144 100644
--- a/cmd/podman/containers/create.go
+++ b/cmd/podman/containers/create.go
@@ -7,6 +7,7 @@ import (
 	"strconv"
 	"strings"
 
+	"github.com/containers/common/pkg/completion"
 	"github.com/containers/common/pkg/config"
 	"github.com/containers/image/v5/transports/alltransports"
 	"github.com/containers/podman/v3/cmd/podman/common"
@@ -49,12 +50,20 @@ var (
 )
 
 var (
-	cliVals common.ContainerCLIOpts
+	cliVals           common.ContainerCLIOpts
+	InitContainerType string
 )
 
 func createFlags(cmd *cobra.Command) {
 	flags := cmd.Flags()
 
+	initContainerFlagName := "init-ctr"
+	flags.StringVar(
+		&InitContainerType,
+		initContainerFlagName, "",
+		"Make this a pod init container.",
+	)
+
 	flags.SetInterspersed(false)
 	common.DefineCreateFlags(cmd, &cliVals)
 	common.DefineNetFlags(cmd)
@@ -65,6 +74,8 @@ func createFlags(cmd *cobra.Command) {
 		_ = flags.MarkHidden("conmon-pidfile")
 		_ = flags.MarkHidden("pidfile")
 	}
+
+	_ = cmd.RegisterFlagCompletionFunc(initContainerFlagName, completion.AutocompleteDefault)
 }
 
 func init() {
@@ -89,6 +100,17 @@ func create(cmd *cobra.Command, args []string) error {
 		return err
 	}
 
+	// Check if initctr is used with --pod and the value is correct
+	if initctr := InitContainerType; cmd.Flags().Changed("init-ctr") {
+		if !cmd.Flags().Changed("pod") {
+			return errors.New("must specify pod value with init-ctr")
+		}
+		if !util.StringInSlice(initctr, []string{"always", "oneshot"}) {
+			return errors.New("init-ctr value must be 'always' or 'oneshot'")
+		}
+		cliVals.InitContainerType = initctr
+	}
+
 	if err := createInit(cmd); err != nil {
 		return err
 	}