Remove docker/ prefix from log messages tag.

This fix tries to address the issue raised in #22358 where syslog's
message tag always starts with `docker/` and can not be removed
by changing the log tag templates.

The issue is that syslog driver hardcodes `path.Base(os.Args[0])`
as the prefix, which is the binary file name of the daemon (`dockerd`).
This could be an issue for certain situations (e.g., #22358) where
user may prefer not to have a dedicated prefix in syslog messages.
There is no way to override this behavior in the current verison of
the docker.

This fix tries to address this issue without making changes in the
default behavior of the syslog driver. An additional
`{{.DaemonName}}` has been introduced in the syslog tag. This is
assigned as the `docker` when daemon starts. The default log tag
template has also been changed from
`path.Base(os.Args[0]) + "/{{.ID}}"` to `{{.DaemonName}}/{{.ID}}`.
Therefore, there is no behavior changes when log-tag is not provided.

In order to be consistent, the default log tag for fluentd has been
changed from `docker.{{.ID}}` to `{{DaemonName}}.{{.ID}}` as well.

The documentation for log-tag has been updated to reflect this change.

Additional test cases have been added to cover changes in this fix.

This fix fixes #22358.

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

container/container.go

@@ -315,6 +315,7 @@ func (container *Container) StartLogger(cfg containertypes.LogConfig) (logger.Lo
 		ContainerCreated:    container.Created,
 		ContainerEnv:        container.Config.Env,
 		ContainerLabels:     container.Config.Labels,
+		DaemonName:          "docker",
 	}
 
 	// Set logging file for "json-logger"

daemon/logger/context.go

@@ -20,6 +20,7 @@ type Context struct {
 	ContainerEnv        []string
 	ContainerLabels     map[string]string
 	LogPath             string
+	DaemonName          string
 }
 
 // ExtraAttributes returns the user-defined extra attributes (labels,

daemon/logger/fluentd/fluentd.go

@@ -65,7 +65,7 @@ func New(ctx logger.Context) (logger.Logger, error) {
 		return nil, err
 	}
 
-	tag, err := loggerutils.ParseLogTag(ctx, "docker.{{.ID}}")
+	tag, err := loggerutils.ParseLogTag(ctx, "{{.DaemonName}}.{{.ID}}")
 	if err != nil {
 		return nil, err
 	}

daemon/logger/loggerutils/log_tag_test.go

@@ -18,6 +18,12 @@ func TestParseLogTag(t *testing.T) {
 	assertTag(t, e, tag, "test-image/test-container/container-ab")
 }
 
+func TestParseLogTagEmptyTag(t *testing.T) {
+	ctx := buildContext(map[string]string{})
+	tag, e := ParseLogTag(ctx, "{{.DaemonName}}/{{.ID}}")
+	assertTag(t, e, tag, "test-dockerd/container-ab")
+}
+
 // Helpers
 
 func buildContext(cfg map[string]string) logger.Context {
@@ -27,6 +33,7 @@ func buildContext(cfg map[string]string) logger.Context {
 		ContainerImageID:   "image-abcdefghijklmnopqrstuvwxyz01234567890",
 		ContainerImageName: "test-image",
 		Config:             cfg,
+		DaemonName:         "test-dockerd",
 	}
 }
 

daemon/logger/syslog/syslog.go

@@ -10,7 +10,6 @@ import (
 	"net"
 	"net/url"
 	"os"
-	"path"
 	"strconv"
 	"strings"
 	"time"
@@ -91,7 +90,7 @@ func rfc5424microformatterWithAppNameAsTag(p syslog.Priority, hostname, tag, con
 // the context. Supported context configuration variables are
 // syslog-address, syslog-facility, syslog-format.
 func New(ctx logger.Context) (logger.Logger, error) {
-	tag, err := loggerutils.ParseLogTag(ctx, "{{.ID}}")
+	tag, err := loggerutils.ParseLogTag(ctx, "{{.DaemonName}}/{{.ID}}")
 	if err != nil {
 		return nil, err
 	}
@@ -111,17 +110,15 @@ func New(ctx logger.Context) (logger.Logger, error) {
 		return nil, err
 	}
 
-	logTag := path.Base(os.Args[0]) + "/" + tag
-
 	var log *syslog.Writer
 	if proto == secureProto {
 		tlsConfig, tlsErr := parseTLSConfig(ctx.Config)
 		if tlsErr != nil {
 			return nil, tlsErr
 		}
-		log, err = syslog.DialWithTLSConfig(proto, address, facility, logTag, tlsConfig)
+		log, err = syslog.DialWithTLSConfig(proto, address, facility, tag, tlsConfig)
 	} else {
-		log, err = syslog.Dial(proto, address, facility, logTag)
+		log, err = syslog.Dial(proto, address, facility, tag)
 	}
 
 	if err != nil {

docs/admin/logging/log_tags.md

@@ -30,6 +30,7 @@ Docker supports some special template markup you can use when specifying a tag's
 | `{{.ImageID}}`     | The first 12 characters of the container's image id. |
 | `{{.ImageFullID}}` | The container's full image identifier.               |
 | `{{.ImageName}}`   | The name of the image used by the container.         |
+| `{{.DaemonName}}`  | The name of the docker program (`docker`).           |
 
 For example, specifying a `--log-opt tag="{{.ImageName}}/{{.Name}}/{{.ID}}"` value yields `syslog` log lines like: