kube play: support auto updates and rollbacks

Add auto-update support to `podman kube play`.  Auto-update policies can
be configured for:
 * the entire pod via the `io.containers.autoupdate` annotation
 * a specific container via the `io.containers.autoupdate/$name` annotation

To make use of rollbacks, the `io.containers.sdnotify` policy should be
set to `container` such that the workload running _inside_ the container
can send the READY message via the NOTIFY_SOCKET once ready.  For
further details on auto updates and rollbacks, please refer to the
specific article [1].

Since auto updates and rollbacks bases on Podman's systemd integration,
the k8s YAML must be executed in the `podman-kube@` systemd template.
For further details on how to run k8s YAML in systemd via Podman, please
refer to the specific article [2].

An examplary k8s YAML may look as follows:
```YAML
apiVersion: v1
kind: Pod
metadata:
  annotations:
      io.containers.autoupdate: "local"
      io.containers.autoupdate/b: "registry"
  labels:
    app: test
  name: test_pod
spec:
  containers:
  - command:
    - top
    image: alpine
    name: a
  - command:
    - top
    image: alpine
    name: b
```

[1] https://www.redhat.com/sysadmin/podman-auto-updates-rollbacks
[2] https://www.redhat.com/sysadmin/kubernetes-workloads-podman-systemd

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

1 files changed, 8 insertions, 0 deletions

diff --git a/pkg/specgen/generate/kube/kube.go b/pkg/specgen/generate/kube/kube.go
index 5862d3f1c..9fd0adecf 100644
--- a/pkg/specgen/generate/kube/kube.go
+++ b/pkg/specgen/generate/kube/kube.go
@@ -7,6 +7,7 @@ import (
 	"fmt"
 	"math"
 	"net"
+	"os"
 	"regexp"
 	"runtime"
 	"strconv"
@@ -26,6 +27,7 @@ import (
 	"github.com/containers/podman/v4/pkg/k8s.io/apimachinery/pkg/api/resource"
 	"github.com/containers/podman/v4/pkg/specgen"
 	"github.com/containers/podman/v4/pkg/specgen/generate"
+	systemdDefine "github.com/containers/podman/v4/pkg/systemd/define"
 	"github.com/containers/podman/v4/pkg/util"
 	"github.com/docker/docker/pkg/system"
 	"github.com/docker/go-units"
@@ -445,6 +447,12 @@ func ToSpecGen(ctx context.Context, opts *CtrSpecGenOptions) (*specgen.SpecGener
 		}
 	}
 
+	// Make sure the container runs in a systemd unit which is
+	// stored as a label at container creation.
+	if unit := os.Getenv(systemdDefine.EnvVariable); unit != "" {
+		s.Labels[systemdDefine.EnvVariable] = unit
+	}
+
 	return s, nil
 }