fix: make cni logs available via kubectl logs (#4845)

* fix(cni): make cni logs available via kubectl logs

Signed-off-by: slonka <slonka@users.noreply.github.com>

app/cni/pkg/cni/main.go

@@ -5,6 +5,9 @@ import (
 	"encoding/json"
 	"fmt"
 	"net"
+	"os"
+	"path"
+	"strconv"
 	"time"
 
 	"github.com/containernetworking/cni/pkg/skel"
@@ -24,10 +27,13 @@ import (
 const (
 	podRetrievalMaxRetries = 30
 	podRetrievalInterval   = 1 * time.Second
+	defaultLogLocation     = "/tmp/kuma-cni.log"
+	defaultLogLevel        = 2
+	defaultLogName         = "kuma-cni"
 )
 
 var (
-	log = core.NewLoggerWithRotation(2, "/tmp/kuma-cni.log", 100, 0, 0).WithName("kuma-cni")
+	log = core.NewLoggerWithRotation(defaultLogLevel, defaultLogLocation, 100, 0, 0).WithName(defaultLogName)
 )
 
 // Kubernetes a K8s specific struct to hold config
@@ -85,13 +91,43 @@ func parseConfig(stdin []byte) (*PluginConf, error) {
 	return &conf, nil
 }
 
+func hijackMainProcessStderr() *os.File {
+	file, err := getCniProcessStderr()
+	if err != nil {
+		log.Error(err, "could not hijack main process file - continue logging to "+defaultLogLocation)
+		return nil
+	}
+	log.V(0).Info("successfully hijacked stderr of cni process - logs will be available in 'kubectl logs'")
+	os.Stderr = file
+	log = core.NewLoggerTo(os.Stderr, 2).WithName(defaultLogName)
+	return file
+}
+
+func getCniProcessStderr() (*os.File, error) {
+	pids, err := pidOf("/install-cni")
+	if err != nil {
+		return nil, err
+	}
+	if len(pids) != 1 {
+		return nil, errors.New("more than one process '/install-cni' running on a node, this should not happen")
+	}
+
+	file, err := os.OpenFile(path.Join("/", "proc", strconv.Itoa(pids[0]), "fd", "2"), os.O_WRONLY, 0)
+	return file, err
+}
+
 // cmdAdd is called for ADD requests
 func cmdAdd(args *skel.CmdArgs) error {
 	ctx := context.Background()
 	conf, err := parseConfig(args.StdinData)
 	if err != nil {
 		return errors.Wrap(err, "error parsing kuma-cni cmdAdd config")
 	}
+
+	mainProcessStderr := hijackMainProcessStderr()
+	if mainProcessStderr != nil {
+		defer mainProcessStderr.Close()
+	}
 	logPrevResult(conf)
 
 	// Determine if running under k8s by checking the CNI args

app/cni/pkg/cni/utils.go

@@ -0,0 +1,84 @@
+package cni
+
+import (
+	"bytes"
+	"errors"
+	"io"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"strconv"
+	"strings"
+	"unicode"
+)
+
+// PidOf Find process(es) with a specified name (string match)
+// copied from https://github.com/kubernetes/kubernetes/blob/v1.24.3/pkg/util/procfs/procfs_linux.go#L99
+// with small modifications
+// and return their pid(s)
+func pidOf(name string) ([]int, error) {
+	if len(name) == 0 {
+		return []int{}, errors.New("name should not be empty")
+	}
+	return getPids(name), nil
+}
+
+// we don't need regex so this is changed to "string"
+func getPids(name string) []int {
+	pids := []int{}
+
+	dirFD, err := os.Open("/proc")
+	if err != nil {
+		return nil
+	}
+	defer dirFD.Close()
+
+	for {
+		// Read a small number at a time in case there are many entries, we don't want to
+		// allocate a lot here.
+		ls, err := dirFD.Readdir(10)
+		if err == io.EOF {
+			break
+		}
+		if err != nil {
+			return nil
+		}
+
+		for _, entry := range ls {
+			if !entry.IsDir() {
+				continue
+			}
+
+			// If the directory is not a number (i.e. not a PID), skip it
+			pid, err := strconv.Atoi(entry.Name())
+			if err != nil {
+				continue
+			}
+
+			cmdline, err := ioutil.ReadFile(filepath.Join("/proc", entry.Name(), "cmdline"))
+			if err != nil {
+				continue
+			}
+
+			// The bytes we read have '\0' as a separator for the command line
+			parts := bytes.SplitN(cmdline, []byte{0}, 2)
+			if len(parts) == 0 {
+				continue
+			}
+			// Split the command line itself we are interested in just the first part
+			exe := strings.FieldsFunc(string(parts[0]), func(c rune) bool {
+				return unicode.IsSpace(c) || c == ':'
+			})
+			if len(exe) == 0 {
+				continue
+			}
+			// Check if the name of the executable is what we are looking for
+			if name == exe[0] {
+				// Grab the PID from the directory path
+				pids = append(pids, pid)
+			}
+		}
+	}
+
+	return pids
+}

app/cni/pkg/install/main.go

@@ -28,7 +28,7 @@ const (
 )
 
 var (
-	log = core.NewLoggerWithRotation(2, "/tmp/install-cni.log", 100, 0, 0).WithName("install-cni")
+	log = core.NewLoggerTo(os.Stderr, 2).WithName("install-cni")
 )
 
 func removeBinFiles() error {

pkg/core/alias.go

@@ -17,6 +17,7 @@ var (
 	// TODO remove dependency on kubernetes see: https://github.com/kumahq/kuma/issues/2798
 	Log                   = kube_log.Log
 	NewLogger             = kuma_log.NewLogger
+	NewLoggerTo           = kuma_log.NewLoggerTo
 	NewLoggerWithRotation = kuma_log.NewLoggerWithRotation
 	SetLogger             = kube_log.SetLogger
 	Now                   = time.Now