Add writing to CWAgent's log before a panic

cfg/aws/refreshable_shared_credentials_provider.go

@@ -22,7 +22,7 @@ type Refreshable_shared_credentials_provider struct {
 func (p *Refreshable_shared_credentials_provider) Retrieve() (credentials.Value, error) {
 
 	p.SetExpiration(time.Now().Add(p.ExpiryWindow), 0)
-	creds, e := p.sharedCredentialsProvider.Retrieve()
+	creds, err := p.sharedCredentialsProvider.Retrieve()
 
-	return creds, e
+	return creds, err
 }

cmd/config-downloader/downloader.go

@@ -6,8 +6,8 @@ package main
 import (
 	"flag"
 	"io/ioutil"
+	"log"
 	"os"
-
 	"strings"
 
 	configaws "github.com/aws/amazon-cloudwatch-agent/cfg/aws"
@@ -125,26 +125,24 @@ func main() {
 	if inputConfig != "" {
 		f, err := os.Open(inputConfig)
 		if err != nil {
-			fmt.Printf("E! Failed to open Common Config: %v\n", err)
-			panic(err)
+			log.Panicf("E! Failed to open Common Config: %v", err)
 		}
 
 		if err := cc.Parse(f); err != nil {
-			fmt.Printf("E! Failed to parse Common Config: %v\n", err)
-			panic(err)
+			log.Panicf("E! Failed to open Common Config: %v", err)
 		}
 	}
 	util.SetProxyEnv(cc.ProxyMap())
 	util.SetSSLEnv(cc.SSLMap())
 	var errorMessage string
 	if downloadLocation == "" || outputDir == "" {
-		executable, e := os.Executable()
-		if e == nil {
-			errorMessage = fmt.Sprintf("usage: " + filepath.Base(executable) + " --output-dir <path> --download-source ssm:<parameter-store-name> ")
+		executable, err := os.Executable()
+		if err == nil {
+			errorMessage = fmt.Sprintf("E! usage: " + filepath.Base(executable) + " --output-dir <path> --download-source ssm:<parameter-store-name> ")
 		} else {
-			errorMessage = fmt.Sprintf("usage: --output-dir <path> --download-source ssm:<parameter-store-name> ")
+			errorMessage = fmt.Sprintf("E! usage: --output-dir <path> --download-source ssm:<parameter-store-name> ")
 		}
-		panic(errorMessage)
+		log.Panicf(errorMessage)
 	}
 
 	mode = sdkutil.DetectAgentMode(mode)
@@ -154,12 +152,12 @@ func main() {
 	if region == "" && downloadLocation != locationDefault {
 		fmt.Println("Unable to determine aws-region.")
 		if mode == config.ModeEC2 {
-			errorMessage = fmt.Sprintf("Please check if you can access the metadata service. For exampe, on linux, run 'wget -q -O - http://169.254.169.254/latest/meta-data/instance-id && echo' ")
+			errorMessage = fmt.Sprintf("E! Please check if you can access the metadata service. For example, on linux, run 'wget -q -O - http://169.254.169.254/latest/meta-data/instance-id && echo' ")
 		} else {
-			errorMessage = fmt.Sprintf("Please make sure the credentials and region set correctly on your hosts.\n" +
+			errorMessage = fmt.Sprintf("E! Please make sure the credentials and region set correctly on your hosts.\n" +
 				"Refer to http://docs.aws.amazon.com/cli/latest/userguide/cli-chap-getting-started.html")
 		}
-		panic(errorMessage)
+		log.Panicf(errorMessage)
 	}
 
 	// clean up output dir for tmp files before writing out new tmp file.
@@ -187,7 +185,7 @@ func main() {
 
 	locationArray := strings.SplitN(downloadLocation, locationSeparator, 2)
 	if locationArray == nil || len(locationArray) < 2 && downloadLocation != locationDefault {
-		panic(fmt.Sprintf("downloadLocation %s is malformated.\n", downloadLocation))
+		log.Panicf("E! downloadLocation %s is malformated.", downloadLocation)
 	}
 
 	var config, outputFilePath string
@@ -209,25 +207,25 @@ func main() {
 			config, err = readFromFile(locationArray[1])
 		}
 	default:
-		panic(fmt.Sprintf("location type %s is not supported.", locationArray[0]))
+		log.Panicf("E! Location type %s is not supported.", locationArray[0])
 	}
 
 	if err != nil {
-		panic(fmt.Sprintf("Fail to fetch/remove json config: %v\n", err))
+		log.Panicf("E! Fail to fetch/remove json config: %v", err)
 	}
 
 	if multiConfig != "remove" {
 		outputFilePath = filepath.Join(outputDir, outputFilePath+context.TmpFileSuffix)
 		err = ioutil.WriteFile(outputFilePath, []byte(config), 0644)
 		if err != nil {
-			panic(fmt.Sprintf("Failed to write the json file %v: %v\n", outputFilePath, err))
+			log.Panicf("E! Failed to write the json file %v: %v", outputFilePath, err)
 		} else {
 			fmt.Printf("Successfully fetched the config and saved in %s\n", outputFilePath)
 		}
 	} else {
 		outputFilePath = filepath.Join(outputDir, outputFilePath)
 		if err := os.Remove(outputFilePath); err != nil {
-			panic(fmt.Sprintf("Failed to remove the json file %v: %v", outputFilePath, err))
+			log.Panicf("E! Failed to remove the json file %v: %v", outputFilePath, err)
 		} else {
 			fmt.Printf("Successfully removed the config file %s\n", outputFilePath)
 		}

cmd/config-translator/translator.go

@@ -5,7 +5,6 @@ package main
 
 import (
 	"flag"
-	"fmt"
 	"log"
 	"os"
 	"os/user"
@@ -90,16 +89,16 @@ func main() {
 
 	mergedJsonConfigMap, err := cmdutil.GenerateMergedJsonConfigMap(ctx)
 	if err != nil {
-		panic(fmt.Sprintf("E! Failed to generate merged json config: %v", err))
+		log.Panicf("E! Failed to generate merged json config: %v", err)
 	}
 
 	if !ctx.RunInContainer() {
 		// run as user only applies to non container situation.
-		current, e := user.Current()
-		if e == nil && current.Name == "root" {
+		current, err := user.Current()
+		if err == nil && current.Name == "root" {
 			runAsUser, err := cmdutil.DetectRunAsUser(mergedJsonConfigMap)
 			if err != nil {
-				panic("E! Failed to detectRunAsUser\n")
+				log.Panic("E! Failed to detectRunAsUser")
 			}
 			cmdutil.VerifyCredentials(ctx, runAsUser)
 		}

integration/clean/clean_ami.go

@@ -8,13 +8,14 @@ package main
 
 import (
 	"context"
+	"log"
+	"time"
+
 	"github.com/aws/aws-sdk-go-v2/aws"
 	"github.com/aws/aws-sdk-go-v2/config"
 	"github.com/aws/aws-sdk-go-v2/service/ec2"
 	"github.com/aws/aws-sdk-go-v2/service/ec2/types"
 	smithyTime "github.com/aws/smithy-go/time"
-	"log"
-	"time"
 )
 
 func main() {

integration/test/agent_util.go

@@ -83,7 +83,7 @@ func RunShellScript(path string) {
 }
 
 func ReplaceLocalStackHostName(pathIn string) {
-	out, err := exec.Command("bash", "-c", "sed -i 's/localhost.localstack.cloud/'\"$LOCAL_STACK_HOST_NAME\"'/g' " + pathIn).Output()
+	out, err := exec.Command("bash", "-c", "sed -i 's/localhost.localstack.cloud/'\"$LOCAL_STACK_HOST_NAME\"'/g' "+pathIn).Output()
 
 	if err != nil {
 		log.Fatal(fmt.Sprint(err) + string(out))

integration/test/ca_bundle/ca_bundle_test.go

@@ -50,13 +50,13 @@ func TestBundle(t *testing.T) {
 		log.Printf("resource file location %s find target %t", parameter.dataInput, parameter.findTarget)
 		t.Run(fmt.Sprintf("resource file location %s find target %t", parameter.dataInput, parameter.findTarget), func(t *testing.T) {
 			test.ReplaceLocalStackHostName(parameter.dataInput + configJSON)
-			test.CopyFile(parameter.dataInput + configJSON, configOutputPath)
-			test.CopyFile(parameter.dataInput + commonConfigTOML, commonConfigOutputPath)
-			test.StartAgent(configOutputPath);
-			time.Sleep(agentRuntime);
-			log.Printf("Agent has been running for : %s", agentRuntime.String());
-			test.StopAgent();
-			output := test.ReadAgentOutput(agentRuntime);
+			test.CopyFile(parameter.dataInput+configJSON, configOutputPath)
+			test.CopyFile(parameter.dataInput+commonConfigTOML, commonConfigOutputPath)
+			test.StartAgent(configOutputPath)
+			time.Sleep(agentRuntime)
+			log.Printf("Agent has been running for : %s", agentRuntime.String())
+			test.StopAgent()
+			output := test.ReadAgentOutput(agentRuntime)
 			containsTarget := outputLogContainsTarget(output)
 			if (parameter.findTarget && !containsTarget) || (!parameter.findTarget && containsTarget) {
 				t.Errorf("Find target is %t contains target is %t", parameter.findTarget, containsTarget)

internal/containerinsightscommon/nodeCapacity.go

@@ -18,7 +18,7 @@ type NodeCapacity struct {
 
 func NewNodeCapacity() *NodeCapacity {
 	if _, err := os.Lstat("/rootfs/proc"); os.IsNotExist(err) {
-		panic("/rootfs/proc doesn't exists")
+		log.Panic("E! /rootfs/proc does not exist")
 	}
 	if err := os.Setenv(GoPSUtilProcDirEnv, "/rootfs/proc"); err != nil {
 		log.Printf("E! NodeCapacity cannot set goPSUtilProcDirEnv to /rootfs/proc %v", err)

internal/ecsservicediscovery/containerinstanceprocessor.go

@@ -37,15 +37,15 @@ func NewContainerInstanceProcessor(ecs *ecs.ECS, ec2 *ec2.EC2, s *ProcessorStats
 	// initiate the container instance metadata LRU caching
 	lru, err := simplelru.NewLRU(ec2metadataCacheSize, nil)
 	if err != nil {
-		panic(err)
+		log.Panicf("E! Initial container instance with caching failed because of %v", err)
 	}
 	p.ec2MetaDataCache = lru
 	return p
 }
 
 func splitMapKeys(a map[string]*EC2MetaData, size int) [][]string {
 	if size == 0 {
-		panic("splitMapKeys size cannot be zero.")
+		log.Panic("splitMapKeys size cannot be zero.")
 	}
 
 	result := make([][]string, 0)

internal/ecsservicediscovery/taskdefinitionprocessor.go

@@ -4,6 +4,8 @@
 package ecsservicediscovery
 
 import (
+	"log"
+
 	"github.com/aws/aws-sdk-go/aws"
 	"github.com/aws/aws-sdk-go/service/ecs"
 	"github.com/hashicorp/golang-lru/simplelru"
@@ -31,7 +33,7 @@ func NewTaskDefinitionProcessor(ecs *ecs.ECS, s *ProcessorStats) *TaskDefinition
 	// initiate the caching
 	lru, err := simplelru.NewLRU(taskDefCacheSize, nil)
 	if err != nil {
-		panic(err)
+		log.Panicf("E! Initial task definition with caching failed because of %v", err)
 	}
 	p.taskDefCache = lru
 	return p

internal/publisher/blockingfifoqueue.go

@@ -3,14 +3,18 @@
 
 package publisher
 
+import (
+	"log"
+)
+
 // It is a FIFO queue with the functionality that block the caller if the queue size reaches to the maxSize
 type BlockingFifoQueue struct {
 	queue chan interface{}
 }
 
 func NewBlockingFifoQueue(size int) *BlockingFifoQueue {
 	if size <= 0 {
-		panic("Queue Size should be larger than 0!")
+		log.Panic("E! Queue Size should be larger than 0!")
 	}
 
 	return &BlockingFifoQueue{queue: make(chan interface{}, size)}

internal/publisher/nonblockingfifoqueue.go

@@ -18,7 +18,7 @@ type NonBlockingFifoQueue struct {
 
 func NewNonBlockingFifoQueue(size int) *NonBlockingFifoQueue {
 	if size <= 0 {
-		panic("Queue Size should be larger than 0!")
+		log.Panic("E! Queue Size should be larger than 0!")
 	}
 	return &NonBlockingFifoQueue{
 		queue:   list.New(),

internal/publisher/nonblockinglifoqueue.go

@@ -25,7 +25,7 @@ type node struct {
 
 func NewNonBlockingLifoQueue(size int) *NonBlockingLifoQueue {
 	if size <= 0 {
-		panic("Queue Size should be larger than 0!")
+		log.Panic("E! Queue Size should be larger than 0!")
 	}
 	return &NonBlockingLifoQueue{maxSize: size}
 }

plugins/inputs/cadvisor/cadvisor_linux.go

@@ -86,7 +86,7 @@ func (c *Cadvisor) Gather(acc telegraf.Accumulator) error {
 	var err error
 
 	if c.manager == nil && c.initManager() != nil {
-		panic("Cannot initiate manager")
+		log.Panic("E! Cannot initiate manager")
 	}
 
 	req := &cinfo.ContainerInfoRequest{

plugins/inputs/logfile/logfile_test.go

@@ -404,7 +404,7 @@ func TestLogsFileAutoRemoval(t *testing.T) {
 	}()
 
 	wg.Add(1)
-	
+
 	go func() {
 		defer wg.Done()
 

plugins/inputs/logfile/tail/tail.go

@@ -465,7 +465,7 @@ func (tail *Tail) waitForChanges() error {
 	case <-tail.Dying():
 		return ErrStop
 	}
-	panic("unreachable")
+
 }
 
 func (tail *Tail) openReader() {
@@ -593,7 +593,7 @@ func (tail *Tail) exitOnDeletion() {
 // with the last chunk of variable size.
 func partitionString(s string, chunkSize int) []string {
 	if chunkSize <= 0 {
-		panic("invalid chunkSize")
+		panic("Invalid chunkSize")
 	}
 	length := len(s)
 	chunks := 1 + length/chunkSize

plugins/inputs/logfile/tail/watch/inotify.go

@@ -61,7 +61,6 @@ func (fw *InotifyFileWatcher) BlockUntilExists(t *tomb.Tomb) error {
 			return tomb.ErrDying
 		}
 	}
-	panic("unreachable")
 }
 
 func (fw *InotifyFileWatcher) ChangeEvents(t *tomb.Tomb, pos int64) (*FileChanges, error) {

plugins/inputs/logfile/tail/watch/polling.go

@@ -39,7 +39,6 @@ func (fw *PollingFileWatcher) BlockUntilExists(t *tomb.Tomb) error {
 			return tomb.ErrDying
 		}
 	}
-	panic("unreachable")
 }
 
 func (fw *PollingFileWatcher) ChangeEvents(t *tomb.Tomb, pos int64) (*FileChanges, error) {

plugins/inputs/logfile/tail/winfile/winfile.go

@@ -55,8 +55,8 @@ func Open(path string, mode int, perm uint32) (fd syscall.Handle, err error) {
 	default:
 		createmode = syscall.OPEN_EXISTING
 	}
-	h, e := syscall.CreateFile(pathp, access, sharemode, sa, createmode, syscall.FILE_ATTRIBUTE_NORMAL, 0)
-	return h, e
+	h, err := syscall.CreateFile(pathp, access, sharemode, sa, createmode, syscall.FILE_ATTRIBUTE_NORMAL, 0)
+	return h, err
 }
 
 // https://github.com/jnwhiteh/golang/blob/master/src/pkg/syscall/syscall_windows.go#L211
@@ -69,9 +69,9 @@ func makeInheritSa() *syscall.SecurityAttributes {
 
 // https://github.com/jnwhiteh/golang/blob/master/src/pkg/os/file_windows.go#L133
 func OpenFile(name string, flag int, perm os.FileMode) (file *os.File, err error) {
-	r, e := Open(name, flag|syscall.O_CLOEXEC, syscallMode(perm))
-	if e != nil {
-		return nil, e
+	r, err := Open(name, flag|syscall.O_CLOEXEC, syscallMode(perm))
+	if err != nil {
+		return nil, err
 	}
 	return os.NewFile(uintptr(r), name), nil
 }

plugins/inputs/prometheus_scraper/metrics_receiver_test.go

@@ -20,9 +20,9 @@ func Test_metricAppender_Add_BadMetricName(t *testing.T) {
 		{Name: "name_b", Value: "value_b"},
 	}
 
-	r, e := ma.Add(ls, ts, v)
+	r, err := ma.Add(ls, ts, v)
 	assert.Equal(t, uint64(0), r)
-	assert.Equal(t, "metricName of the times-series is missing", e.Error())
+	assert.Equal(t, "metricName of the times-series is missing", err.Error())
 }
 
 func Test_metricAppender_Add(t *testing.T) {
@@ -35,9 +35,9 @@ func Test_metricAppender_Add(t *testing.T) {
 		{Name: "tag_a", Value: "a"},
 	}
 
-	ref, e := ma.Add(ls, ts, v)
+	ref, err := ma.Add(ls, ts, v)
 	assert.Equal(t, ref, uint64(0))
-	assert.Nil(t, e)
+	assert.Nil(t, err)
 	mac, _ := ma.(*metricAppender)
 	assert.Equal(t, 1, len(mac.batch))
 
@@ -68,9 +68,9 @@ func Test_metricAppender_Rollback(t *testing.T) {
 		{Name: "tag_a", Value: "a"},
 	}
 
-	ref, e := ma.Add(ls, ts, v)
+	ref, err := ma.Add(ls, ts, v)
 	assert.Equal(t, ref, uint64(0))
-	assert.Nil(t, e)
+	assert.Nil(t, err)
 	mac, _ := ma.(*metricAppender)
 	assert.Equal(t, 1, len(mac.batch))
 
@@ -89,12 +89,12 @@ func Test_metricAppender_Commit(t *testing.T) {
 		{Name: "tag_a", Value: "a"},
 	}
 
-	ref, e := ma.Add(ls, ts, v)
+	ref, err := ma.Add(ls, ts, v)
 	assert.Equal(t, ref, uint64(0))
-	assert.Nil(t, e)
+	assert.Nil(t, err)
 	mac, _ := ma.(*metricAppender)
 	assert.Equal(t, 1, len(mac.batch))
-	err := ma.Commit()
+	err = ma.Commit()
 	assert.Equal(t, nil, err)
 
 	pmb := <-mbCh