fn: introducing docker-syslog driver as default logger (#1189)

* fn: introducing docker-syslog driver as default logger

With this change, fn-agent prefers RFC2454 docker-syslog driver
for logging stdout/stderr from containers. The advantage
of this is to offload it to docker itself instead of
streaming stderr along with stdout, which gets multiplexed
through single connection via docker-API.

The change will need support from FDKs in order to log
correct call-id and supress '\n' that splits syslog lines.

api/agent/agent.go

@@ -5,7 +5,6 @@ import (
 	"context"
 	"errors"
 	"io"
-	"log/syslog"
 	"strings"
 	"sync"
 	"sync/atomic"
@@ -696,7 +695,7 @@ type hotSlot struct {
 	done          chan struct{} // signal we are done with slot
 	errC          <-chan error  // container error
 	container     *container    // TODO mask this
-	maxRespSize   uint64        // TODO boo.
+	cfg           *Config
 	fatalErr      error
 	containerSpan trace.SpanContext
 }
@@ -741,23 +740,10 @@ func (s *hotSlot) exec(ctx context.Context, call *call) error {
 	// NOTE: stderr is limited separately (though line writer is vulnerable to attack?)
 	// limit the bytes allowed to be written to the stdout pipe, which handles any
 	// buffering overflows (json to a string, http to a buffer, etc)
-	stdoutWrite := common.NewClampWriter(stdoutWritePipe, s.maxRespSize, models.ErrFunctionResponseTooBig)
+	stdoutWrite := common.NewClampWriter(stdoutWritePipe, s.cfg.MaxResponseSize, models.ErrFunctionResponseTooBig)
-
-	// get our own syslogger with THIS call id (cheap), using the container's already open syslog conns (expensive)
-	// TODO? we can basically just do this whether there are conns or not, this is relatively cheap (despite appearances)
-	buf1 := bufPool.Get().(*bytes.Buffer)
-	buf2 := bufPool.Get().(*bytes.Buffer)
-	defer bufPool.Put(buf1)
-	defer bufPool.Put(buf2)
-
-	sw := newSyslogWriter(call.ID, call.Path, call.AppName, syslog.LOG_ERR, s.container.syslogConns, buf1)
-	var syslog io.WriteCloser = &nopCloser{sw}
-	syslog = newLineWriterWithBuffer(buf2, syslog)
-	defer syslog.Close()                            // close syslogger from here, but NOT the call log stderr OR conns
-	stderr := multiWriteCloser{call.stderr, syslog} // use multiWriteCloser for its error ignoring properties
 
 	proto := protocol.New(protocol.Protocol(call.Format), stdinWrite, stdoutRead)
-	swapBack := s.container.swap(stdinRead, stdoutWrite, stderr, &call.Stats)
+	swapBack := s.container.swap(stdinRead, stdoutWrite, call.stderr, &call.Stats)
 	defer swapBack() // NOTE: it's important this runs before the pipes are closed.
 
 	errApp := make(chan error, 1)
@@ -815,10 +801,17 @@ func (a *agent) prepCold(ctx context.Context, call *call, tok ResourceToken, ch
 		cpus:    uint64(call.CPUs),
 		fsSize:  a.cfg.MaxFsSize,
 		timeout: time.Duration(call.Timeout) * time.Second, // this is unnecessary, but in case removal fails...
-		stdin:   call.req.Body,
+		logCfg: drivers.LoggerConfig{
-		stdout:  common.NewClampWriter(call.w, a.cfg.MaxResponseSize, models.ErrFunctionResponseTooBig),
+			URL: strings.TrimSpace(call.SyslogURL),
-		stderr:  call.stderr,
+			Tags: []drivers.LoggerTag{
-		stats:   &call.Stats,
+				{Name: "app_name", Value: call.AppName},
+				{Name: "func_name", Value: call.Path},
+			},
+		},
+		stdin:  call.req.Body,
+		stdout: common.NewClampWriter(call.w, a.cfg.MaxResponseSize, models.ErrFunctionResponseTooBig),
+		stderr: call.stderr,
+		stats:  &call.Stats,
 	}
 
 	cookie, err := a.driver.CreateCookie(ctx, container)
@@ -899,7 +892,7 @@ func (a *agent) runHot(ctx context.Context, call *call, tok ResourceToken, state
 				done:          make(chan struct{}),
 				errC:          errC,
 				container:     container,
-				maxRespSize:   a.cfg.MaxResponseSize,
+				cfg:           &a.cfg,
 				containerSpan: trace.FromContext(ctx).SpanContext(),
 			}
 			if !a.runHotReq(ctx, call, state, logger, cookie, slot) {
@@ -1028,11 +1021,11 @@ type container struct {
 	fsSize     uint64
 	tmpFsSize  uint64
 	timeout    time.Duration // cold only (superfluous, but in case)
+	logCfg     drivers.LoggerConfig
 
-	stdin       io.Reader
+	stdin  io.Reader
-	stdout      io.Writer
+	stdout io.Writer
-	stderr      io.Writer
+	stderr io.Writer
-	syslogConns io.WriteCloser
 
 	// swapMu protects the stats swapping
 	swapMu sync.Mutex
@@ -1051,13 +1044,6 @@ func newHotContainer(ctx context.Context, call *call, cfg *Config) (*container,
 	stderr := common.NewGhostWriter()
 	stdout := common.NewGhostWriter()
 
-	// these are only the conns, this doesn't write the syslog format (since it will change between calls)
-	syslogConns, err := syslogConns(ctx, call.SyslogURL)
-	if err != nil {
-		// TODO we could write this to between stderr but between stderr doesn't go to user either. kill me.
-		common.Logger(ctx).WithError(err).WithFields(logrus.Fields{"app_id": call.AppID, "path": call.Path, "image": call.Image, "container_id": id}).Error("error dialing syslog urls")
-	}
-
 	// for use if no freezer (or we ever make up our minds)
 	var bufs []*bytes.Buffer
 
@@ -1070,7 +1056,7 @@ func newHotContainer(ctx context.Context, call *call, cfg *Config) (*container,
 
 		// wrap the syslog and debug loggers in the same (respective) line writer
 		// syslog complete chain for this (from top):
-		// stderr -> line writer -> syslog -> []conns
+		// stderr -> line writer
 
 		// TODO(reed): I guess this is worth it
 		// TODO(reed): there's a bug here where the between writers could have
@@ -1079,39 +1065,38 @@ func newHotContainer(ctx context.Context, call *call, cfg *Config) (*container,
 		// and mostly came to the conclusion that life is meaningless.
 		buf1 := bufPool.Get().(*bytes.Buffer)
 		buf2 := bufPool.Get().(*bytes.Buffer)
-		buf3 := bufPool.Get().(*bytes.Buffer)
+		bufs = []*bytes.Buffer{buf1, buf2}
-		buf4 := bufPool.Get().(*bytes.Buffer)
-		bufs = []*bytes.Buffer{buf1, buf2, buf3, buf4}
 
-		// stdout = LOG_INFO, stderr = LOG_ERR -- ONLY for the between writers, normal stdout is a response
+		soc := &nopCloser{&logWriter{
-		so := newSyslogWriter(call.ID, call.Path, call.AppName, syslog.LOG_INFO, syslogConns, buf1)
-		se := newSyslogWriter(call.ID, call.Path, call.AppName, syslog.LOG_ERR, syslogConns, buf2)
-
-		// use multiWriteCloser since it ignores errors (io.MultiWriter does not)
-		soc := multiWriteCloser{&nopCloser{so}, &nopCloser{&logWriter{
 			logrus.WithFields(logrus.Fields{"tag": "stdout", "app_id": call.AppID, "path": call.Path, "image": call.Image, "container_id": id}),
-		}}}
+		}}
-		sec := multiWriteCloser{&nopCloser{se}, &nopCloser{&logWriter{
+		sec := &nopCloser{&logWriter{
 			logrus.WithFields(logrus.Fields{"tag": "stderr", "app_id": call.AppID, "path": call.Path, "image": call.Image, "container_id": id}),
-		}}}
+		}}
 
-		stdout.Swap(newLineWriterWithBuffer(buf4, soc))
+		stdout.Swap(newLineWriterWithBuffer(buf1, soc))
-		stderr.Swap(newLineWriterWithBuffer(buf3, sec))
+		stderr.Swap(newLineWriterWithBuffer(buf2, sec))
 	}
 
 	return &container{
-			id:          id, // XXX we could just let docker generate ids...
+			id:         id, // XXX we could just let docker generate ids...
-			image:       call.Image,
+			image:      call.Image,
-			env:         map[string]string(call.Config),
+			env:        map[string]string(call.Config),
-			extensions:  call.extensions,
+			extensions: call.extensions,
-			memory:      call.Memory,
+			memory:     call.Memory,
-			cpus:        uint64(call.CPUs),
+			cpus:       uint64(call.CPUs),
-			fsSize:      cfg.MaxFsSize,
+			fsSize:     cfg.MaxFsSize,
-			tmpFsSize:   uint64(call.TmpFsSize),
+			tmpFsSize:  uint64(call.TmpFsSize),
-			stdin:       stdin,
+			logCfg: drivers.LoggerConfig{
-			stdout:      stdout,
+				URL: strings.TrimSpace(call.SyslogURL),
-			stderr:      stderr,
+				Tags: []drivers.LoggerTag{
-			syslogConns: syslogConns,
+					{Name: "app_name", Value: call.AppName},
+					{Name: "func_name", Value: call.Path},
+				},
+			},
+			stdin:  stdin,
+			stdout: stdout,
+			stderr: stderr,
 		}, func() {
 			stdin.Close()
 			stderr.Close()
@@ -1119,7 +1104,6 @@ func newHotContainer(ctx context.Context, call *call, cfg *Config) (*container,
 			for _, b := range bufs {
 				bufPool.Put(b)
 			}
-			syslogConns.Close()
 		}
 }
 
@@ -1144,21 +1128,22 @@ func (c *container) swap(stdin io.Reader, stdout, stderr io.Writer, cs *drivers.
 	}
 }
 
-func (c *container) Id() string                     { return c.id }
+func (c *container) Id() string                         { return c.id }
-func (c *container) Command() string                { return "" }
+func (c *container) Command() string                    { return "" }
-func (c *container) Input() io.Reader               { return c.stdin }
+func (c *container) Input() io.Reader                   { return c.stdin }
-func (c *container) Logger() (io.Writer, io.Writer) { return c.stdout, c.stderr }
+func (c *container) Logger() (io.Writer, io.Writer)     { return c.stdout, c.stderr }
-func (c *container) Volumes() [][2]string           { return nil }
+func (c *container) Volumes() [][2]string               { return nil }
-func (c *container) WorkDir() string                { return "" }
+func (c *container) WorkDir() string                    { return "" }
-func (c *container) Close()                         {}
+func (c *container) Close()                             {}
-func (c *container) Image() string                  { return c.image }
+func (c *container) Image() string                      { return c.image }
-func (c *container) Timeout() time.Duration         { return c.timeout }
+func (c *container) Timeout() time.Duration             { return c.timeout }
-func (c *container) EnvVars() map[string]string     { return c.env }
+func (c *container) EnvVars() map[string]string         { return c.env }
-func (c *container) Memory() uint64                 { return c.memory * 1024 * 1024 } // convert MB
+func (c *container) Memory() uint64                     { return c.memory * 1024 * 1024 } // convert MB
-func (c *container) CPUs() uint64                   { return c.cpus }
+func (c *container) CPUs() uint64                       { return c.cpus }
-func (c *container) FsSize() uint64                 { return c.fsSize }
+func (c *container) FsSize() uint64                     { return c.fsSize }
-func (c *container) TmpFsSize() uint64              { return c.tmpFsSize }
+func (c *container) TmpFsSize() uint64                  { return c.tmpFsSize }
-func (c *container) Extensions() map[string]string  { return c.extensions }
+func (c *container) Extensions() map[string]string      { return c.extensions }
+func (c *container) LoggerConfig() drivers.LoggerConfig { return c.logCfg }
 
 // WriteStat publishes each metric in the specified Stats structure as a histogram metric
 func (c *container) WriteStat(ctx context.Context, stat drivers.Stat) {

api/agent/drivers/docker/cookie.go

@@ -25,6 +25,34 @@ type cookie struct {
 	drv *DockerDriver
 }
 
+func (c *cookie) configureLogger(log logrus.FieldLogger) {
+
+	conf := c.task.LoggerConfig()
+	if conf.URL == "" {
+		c.opts.HostConfig.LogConfig = docker.LogConfig{
+			Type: "none",
+		}
+		return
+	}
+
+	c.opts.HostConfig.LogConfig = docker.LogConfig{
+		Type: "syslog",
+		Config: map[string]string{
+			"syslog-address":  conf.URL,
+			"syslog-facility": "user",
+			"syslog-format":   "rfc5424",
+		},
+	}
+
+	tags := make([]string, 0, len(conf.Tags))
+	for _, pair := range conf.Tags {
+		tags = append(tags, fmt.Sprintf("%s=%s", pair.Name, pair.Value))
+	}
+	if len(tags) > 0 {
+		c.opts.HostConfig.LogConfig.Config["tag"] = strings.Join(tags, ",")
+	}
+}
+
 func (c *cookie) configureMem(log logrus.FieldLogger) {
 	if c.task.Memory() == 0 {
 		return

api/agent/drivers/docker/docker.go

@@ -217,15 +217,11 @@ func (drv *DockerDriver) CreateCookie(ctx context.Context, task drivers.Containe
 			Image:        task.Image(),
 			OpenStdin:    true,
 			AttachStdout: true,
-			AttachStderr: true,
 			AttachStdin:  true,
+			AttachStderr: true,
 			StdinOnce:    true,
 		},
-		// turn off logs since we're collecting them from attach
 		HostConfig: &docker.HostConfig{
-			LogConfig: docker.LogConfig{
-				Type: "none",
-			},
 			ReadonlyRootfs: drv.conf.EnableReadOnlyRootFs,
 		},
 		Context: ctx,
@@ -237,6 +233,7 @@ func (drv *DockerDriver) CreateCookie(ctx context.Context, task drivers.Containe
 		drv:  drv,
 	}
 
+	cookie.configureLogger(log)
 	cookie.configureMem(log)
 	cookie.configureCmd(log)
 	cookie.configureEnv(log)

api/agent/drivers/docker/docker_pool.go

@@ -71,6 +71,7 @@ func (c *poolTask) CPUs() uint64                                     { return 0
 func (c *poolTask) FsSize() uint64                                   { return 0 }
 func (c *poolTask) TmpFsSize() uint64                                { return 0 }
 func (c *poolTask) Extensions() map[string]string                    { return nil }
+func (c *poolTask) LoggerConfig() drivers.LoggerConfig               { return drivers.LoggerConfig{} }
 func (c *poolTask) WriteStat(ctx context.Context, stat drivers.Stat) {}
 
 type dockerPoolItem struct {

api/agent/drivers/docker/docker_test.go

@@ -37,6 +37,7 @@ func (f *taskDockerTest) WorkDir() string                         { return "" }
 func (f *taskDockerTest) Close()                                  {}
 func (f *taskDockerTest) Input() io.Reader                        { return f.input }
 func (f *taskDockerTest) Extensions() map[string]string           { return nil }
+func (f *taskDockerTest) LoggerConfig() drivers.LoggerConfig      { return drivers.LoggerConfig{} }
 
 func TestRunnerDocker(t *testing.T) {
 	dkr := NewDocker(drivers.Config{})

api/agent/drivers/driver.go

@@ -86,6 +86,21 @@ type RunResult interface {
 	Status() string
 }
 
+// Logger Tags for container
+type LoggerTag struct {
+	Name  string
+	Value string
+}
+
+// Logger Configuration for container
+type LoggerConfig struct {
+	// Log Sink URL
+	URL string
+
+	// Log Tag Pairs
+	Tags []LoggerTag
+}
+
 // The ContainerTask interface guides container execution across a wide variety of
 // container oriented runtimes.
 type ContainerTask interface {
@@ -136,6 +151,9 @@ type ContainerTask interface {
 	// leaves it unset.
 	WorkDir() string
 
+	// Logger Config to use in driver
+	LoggerConfig() LoggerConfig
+
 	// Close is used to perform cleanup after task execution.
 	// Close should be safe to call multiple times.
 	Close()

api/agent/syslog.go

@@ -1,145 +0,0 @@
-package agent
-
-import (
-	"bytes"
-	"context"
-	"crypto/tls"
-	"fmt"
-	"io"
-	"log/syslog"
-	"net"
-	"net/url"
-	"strings"
-	"time"
-
-	"github.com/fnproject/fn/api/common"
-	"go.opencensus.io/trace"
-)
-
-// syslogConns may return a non-nil io.WriteCloser and an error simultaneously,
-// the error containing any errors from connecting to any of the syslog URLs, and the
-// io.WriteCloser writing to any syslogURLs that were successfully connected to.
-// the returned io.WriteCloser is a Writer to each conn, it should be wrapped in another
-// writer that writes syslog formatted messages (by line).
-func syslogConns(ctx context.Context, syslogURLs string) (io.WriteCloser, error) {
-	// TODO(reed): we should likely add a trace per conn, need to plumb tagging better
-	ctx, span := trace.StartSpan(ctx, "syslog_conns")
-	defer span.End()
-
-	if len(syslogURLs) == 0 {
-		return nullReadWriter{}, nil
-	}
-
-	// gather all the conns, re-use the line we make in the syslogWriter
-	// to write the same bytes to each of the conns.
-	var conns []io.WriteCloser
-	var errs []error
-
-	sinks := strings.Split(syslogURLs, ",")
-	for _, s := range sinks {
-		conn, err := dialSyslog(ctx, strings.TrimSpace(s))
-		if err != nil {
-			errs = append(errs, fmt.Errorf("failed to setup remote syslog connection to %v: %v", s, err))
-			continue
-		}
-
-		conns = append(conns, conn)
-	}
-
-	// do this before checking length of conns
-	var err error
-	if len(errs) > 0 {
-		for _, e := range errs {
-			err = fmt.Errorf("%v%v, ", err, e)
-		}
-	}
-
-	if len(conns) == 0 {
-		return nullReadWriter{}, err
-	}
-
-	return multiWriteCloser(conns), err
-}
-
-func dialSyslog(ctx context.Context, syslogURL string) (io.WriteCloser, error) {
-	url, err := url.Parse(syslogURL)
-	if err != nil {
-		return nil, err
-	}
-
-	common.Logger(ctx).WithField("syslog_url", url).Debug("dialing syslog url")
-
-	var dialer net.Dialer
-	deadline, ok := ctx.Deadline()
-	if ok {
-		dialer.Deadline = deadline
-	}
-
-	// slice off 'xxx://' and dial it
-	switch url.Scheme {
-	case "udp", "tcp":
-		return dialer.Dial(url.Scheme, syslogURL[6:])
-	case "tls":
-		return tls.DialWithDialer(&dialer, "tcp", syslogURL[6:], nil)
-	default:
-		return nil, fmt.Errorf("Unsupported scheme, please use {tcp|udp|tls}: %s: ", url.Scheme)
-	}
-}
-
-// syslogWriter prepends a syslog format with call-specific details
-// for each data segment provided in Write(). This doesn't use
-// log/syslog pkg because we do not need pid for every line (expensive),
-// and we have a format that is easier to read than hiding in preamble.
-// this writes logfmt formatted syslog with values for call, function, and
-// app, it is up to the user to use logfmt from their functions to get a
-// fully formatted line out.
-// TODO not pressing, but we could support json & other formats, too, upon request.
-type syslogWriter struct {
-	pres  []byte
-	post  []byte
-	b     *bytes.Buffer
-	clock func() time.Time
-
-	// the syslog conns (presumably)
-	io.Writer
-}
-
-const severityMask = 0x07
-const facilityMask = 0xf8
-
-func newSyslogWriter(call, function, appName string, severity syslog.Priority, wc io.Writer, buf *bytes.Buffer) *syslogWriter {
-	// Facility = LOG_USER
-	pr := (syslog.LOG_USER & facilityMask) | (severity & severityMask)
-
-	// <priority>VERSION ISOTIMESTAMP HOSTNAME APPLICATION PID      MESSAGEID STRUCTURED-DATA MSG
-	//
-	// and for us:
-	// <22>2             ISOTIMESTAMP fn       appName       funcName callID    -               MSG
-	// ex:
-	//<11>2 2018-02-31T07:42:21Z Fn - - - -  call_id=123 func_name=rdallman/yodawg app_id=123 loggo hereo
-
-	// TODO we could use json for structured data and do that whole thing. up to whoever.
-	return &syslogWriter{
-		pres:   []byte(fmt.Sprintf(`<%d>2`, pr)),
-		post:   []byte(fmt.Sprintf(`fn - - - - call_id=%s func_name=%s app_name=%s `, call, function, appName)),
-		b:      buf,
-		Writer: wc,
-		clock:  time.Now,
-	}
-}
-
-func (sw *syslogWriter) Write(p []byte) (int, error) {
-	// re-use buffer to write in timestamp hodge podge and reduce writes to
-	// the conn by buffering a whole line here before writing to conn.
-
-	buf := sw.b
-	buf.Reset()
-	buf.Write(sw.pres)
-	buf.WriteString(" ")
-	buf.WriteString(sw.clock().UTC().Format(time.RFC3339))
-	buf.WriteString(" ")
-	buf.Write(sw.post)
-	buf.Write(p)
-	n, err := io.Copy(sw.Writer, buf)
-	return int(n), err
-}

api/agent/syslog_test.go

@@ -1,29 +0,0 @@
-package agent
-
-import (
-	"bytes"
-	"log/syslog"
-	"testing"
-	"time"
-)
-
-func TestSyslogFormat(t *testing.T) {
-	var b1 bytes.Buffer
-	var b2 bytes.Buffer
-
-	call := "12345"
-	fn := "yo/dawg"
-	appName := "myapp"
-	now := time.Date(1982, 6, 25, 12, 0, 0, 0, time.UTC)
-	clock := func() time.Time { return now }
-
-	writer := newSyslogWriter(call, fn, appName, syslog.LOG_ERR, &nopCloser{&b1}, &b2)
-	writer.clock = clock
-	writer.Write([]byte("yo"))
-
-	gold := `<11>2 1982-06-25T12:00:00Z fn - - - - call_id=12345 func_name=yo/dawg app_name=myapp yo`
-
-	if b1.String() != gold {
-		t.Fatal("syslog was not what we expected: ", b1.String())
-	}
-}

api/models/app.go

@@ -85,21 +85,19 @@ func (a *App) Validate() error {
 	}
 
 	if a.SyslogURL != nil && *a.SyslogURL != "" {
-		sinks := strings.Split(*a.SyslogURL, ",")
+		url, err := url.Parse(strings.TrimSpace(*a.SyslogURL))
-		for _, s := range sinks {
+		fail := err != nil
-			url, err := url.Parse(strings.TrimSpace(s))
+		if !fail {
-			fail := err != nil
+			// See: https://docs.docker.com/config/containers/logging/syslog/#options
-			if !fail {
+			switch url.Scheme {
-				switch url.Scheme {
+			case "udp", "tcp", "unix", "unixgram", "tcp+tls":
-				case "udp", "tcp", "tls":
+			default:
-				default:
+				fail = true
-					fail = true
-				}
-			}
-			if fail {
-				return ErrInvalidSyslog(fmt.Sprintf(`invalid syslog url: "%v"`, s))
 			}
 		}
+		if fail {
+			return ErrInvalidSyslog(fmt.Sprintf(`invalid syslog url: "%v"`, *a.SyslogURL))
+		}
 	}
 	return nil
 }

docs/operating/logging.md

@@ -13,41 +13,26 @@ All logs are emitted in [logfmt](https://godoc.org/github.com/kr/logfmt) format
 ## Call ID
 
 Every function call/request is assigned a `call_id`. If you search your logs, you can track all the activity
-for each function call and find errors on a call by call basis. For example, these are the log lines for an aynschronous
+for each function call and find errors on a call by call basis.
-function call:
-
-![async logs](/docs/assets/async-log-full.png)
-
-Note the easily searchable `call_id=x` format.
-
-```sh
-call_id=477949e2-922c-5da9-8633-0b2887b79f6e
-```
 
 ## Remote syslog for functions
 
-You may add a syslog url to any function application and all functions that
+Fn uses [docker syslog driver](https://docs.docker.com/config/containers/logging/syslog/) for remote logging if syslog URL is defined for the application. An example syslog URL is:
-exist under that application will ship all of their logs to it. You may
-provide a comma separated list, if desired. Currently, we support `tcp`,
-`udp`, and `tls`, and this will not work if behind a proxy [yet?] (this is my
-life now). This feature only works for 'hot' functions.
-
-An example syslog url is:
 
 ```
-tls://logs.papertrailapp.com:1
+tcp+tls://logs.papertrailapp.com:1
 ```
 
-We log in a syslog format, with some variables added in logfmt format. If you
+See docker syslog driver [syslog-address](https://docs.docker.com/config/containers/logging/syslog/#options) for supported formats.
-find logfmt format offensive, please open an issue and we will consider adding
-more formats (or open a PR that does it, with tests, and you will receive 1
-free cookie along with the feature you want). The logs from the functions
-themselves are not formatted, only our pre-amble, thus, if you'd like a fully
-logfmt line, you must use a logfmt logger to log from your function.
 
-* All log lines are sent as level error w/ the current time and `fn` as hostname.
+Fn adds `func_name` and `app_name` tags to the container logs using [docker syslog driver tags](https://docs.docker.com/config/containers/logging/syslog/#options):
-* call_id, func_name, and app_id will prefix every log line.
 
 ```
-<11>2 1982-06-25T12:00:00Z fn - - - - call_id=12345 func_name=yo/yo app_id=54321 this is your log line
+Aug 29 19:41:31 fnserver 178 <11>1 2018-08-29T19:41:31Z 59ff8628a941 app_name=fn-http-func,func_name=/fn-http-func 17 app_name=fn-http-func,func_name=/fn-http-func - 2018/08/29 19:41:31 Example log output
+Aug 29 19:41:31 fnserver 154 <14>1 2018-08-29T19:41:31Z 59ff8628a941 app_name=fn-http-func,func_name=/fn-http-func 17 app_name=fn-http-func,func_name=/fn-http-func - HTTP/1.1 200 OK
+Aug 29 19:41:31 fnserver 158 <14>1 2018-08-29T19:41:31Z 59ff8628a941 app_name=fn-http-func,func_name=/fn-http-func 17 app_name=fn-http-func,func_name=/fn-http-func - Content-Length: 11
+Aug 29 19:41:31 fnserver 139 <14>1 2018-08-29T19:41:31Z 59ff8628a941 app_name=fn-http-func,func_name=/fn-http-func 17 app_name=fn-http-func,func_name=/fn-http-func - 
+Aug 29 19:41:31 fnserver 761 <14>1 2018-08-29T19:41:31Z 59ff8628a941 app_name=fn-http-func,func_name=/fn-http-func 17 app_name=fn-http-func,func_name=/fn-http-func - Hello World
 ```
+
+Currently, Fn does not add `call_id` to the log tags and it's user function responsibility to include this. FDKs will add support for this.