play kube: service container

Add the notion of a "service container" to play kube.  A service
container is started before the pods in play kube and is (reverse)
linked to them.  The service container is stopped/removed *after*
all pods it is associated with are stopped/removed.

In other words, a service container tracks the entire life cycle
of a service started via `podman play kube`.  This is required to
enable `play kube` in a systemd unit file.

The service container is only used when the `--service-container`
flag is set on the CLI.  This flag has been marked as hidden as it
is not meant to be used outside the context of `play kube`.  It is
further not supported on the remote client.

The wiring with systemd will be done in a later commit.

Signed-off-by: Valentin Rothberg <vrothberg@redhat.com>

1 files changed, 9 insertions, 0 deletions

diff --git a/cmd/podman/play/kube.go b/cmd/podman/play/kube.go
index 5fe059139..f5b121009 100644
--- a/cmd/podman/play/kube.go
+++ b/cmd/podman/play/kube.go
@@ -139,6 +139,15 @@ func init() {
 		flags.StringVar(&kubeOptions.ContextDir, contextDirFlagName, "", "Path to top level of context directory")
 		_ = kubeCmd.RegisterFlagCompletionFunc(contextDirFlagName, completion.AutocompleteDefault)
 
+		// NOTE: The service-container flag is marked as hidden as it
+		// is purely designed for running play-kube in systemd units.
+		// It is not something users should need to know or care about.
+		//
+		// Having a flag rather than an env variable is cleaner.
+		serviceFlagName := "service-container"
+		flags.BoolVar(&kubeOptions.ServiceContainer, serviceFlagName, false, "Starts a service container before all pods")
+		_ = flags.MarkHidden("service-container")
+
 		flags.StringVar(&kubeOptions.SignaturePolicy, "signature-policy", "", "`Pathname` of signature policy file (not usually used)")
 
 		_ = flags.MarkHidden("signature-policy")