kubelet/rkt: Add GetContainerLogs() for rkt.

pkg/kubelet/rkt/log.go

@@ -0,0 +1,50 @@
+/*
+Copyright 2015 Google Inc. All rights reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package rkt
+
+import (
+	"io"
+	"os/exec"
+	"strconv"
+
+	kubecontainer "github.com/GoogleCloudPlatform/kubernetes/pkg/kubelet/container"
+)
+
+// GetContainerLogs uses journalctl to get the logs of the container.
+// By default, it returns a snapshot of the container log. Set |follow| to true to
+// stream the log. Set |follow| to false and specify the number of lines (e.g.
+// "100" or "all") to tail the log.
+// TODO(yifan): Currently, it fetches all the containers' log within a pod. We will
+// be able to fetch individual container's log once https://github.com/coreos/rkt/pull/841
+// landed.
+func (r *Runtime) GetContainerLogs(pod kubecontainer.Pod, tail string, follow bool, stdout, stderr io.Writer) error {
+	unitName := makePodServiceFileName(pod.ID)
+	cmd := exec.Command("journalctl", "-u", unitName)
+	if follow {
+		cmd.Args = append(cmd.Args, "-f")
+	}
+	if tail == "all" {
+		cmd.Args = append(cmd.Args, "-a")
+	} else {
+		_, err := strconv.Atoi(tail)
+		if err == nil {
+			cmd.Args = append(cmd.Args, "-n", tail)
+		}
+	}
+	cmd.Stdout, cmd.Stderr = stdout, stderr
+	return cmd.Start()
+}

pkg/kubelet/rkt/rkt.go

@@ -22,6 +22,7 @@ import (
 	"strings"
 
 	"github.com/GoogleCloudPlatform/kubernetes/pkg/credentialprovider"
+	"github.com/GoogleCloudPlatform/kubernetes/pkg/types"
 	"github.com/coreos/go-systemd/dbus"
 	"github.com/golang/glog"
 )
@@ -142,3 +143,9 @@ func (r *Runtime) runCommand(args ...string) ([]string, error) {
 	}
 	return strings.Split(strings.TrimSpace(string(output)), "\n"), nil
 }
+
+// makePodServiceFileName constructs the unit file name for a pod using its UID.
+func makePodServiceFileName(uid types.UID) string {
+	// TODO(yifan): Revisit this later, decide whether we want to use UID.
+	return fmt.Sprintf("%s_%s.service", kubernetesUnitPrefix, uid)
+}