Add monitor http endpoint

api/agent.go

@@ -1,6 +1,7 @@
 package api
 
 import (
+	"bufio"
 	"fmt"
 )
 
@@ -411,3 +412,37 @@ func (a *Agent) DisableNodeMaintenance() error {
 	resp.Body.Close()
 	return nil
 }
+
+// Monitor returns a channel which will receive streaming logs from the agent
+// Providing a non-nil stopCh can be used to close the connection and stop the
+// log stream
+func (a *Agent) Monitor(loglevel string, stopCh chan struct{}) (chan string, error) {
+	r := a.c.newRequest("GET", "/v1/agent/monitor")
+	if loglevel != "" {
+		r.params.Add("loglevel", loglevel)
+	}
+	_, resp, err := requireOK(a.c.doRequest(r))
+	if err != nil {
+		return nil, err
+	}
+
+	logCh := make(chan string, 64)
+	go func() {
+		defer resp.Body.Close()
+
+		scanner := bufio.NewScanner(resp.Body)
+		for {
+			select {
+			case <-stopCh:
+				close(logCh)
+				return
+			default:
+			}
+			if scanner.Scan() {
+				logCh <- scanner.Text()
+			}
+		}
+	}()
+
+	return logCh, nil
+}

api/agent_test.go

@@ -3,6 +3,7 @@ package api
 import (
 	"strings"
 	"testing"
+	"time"
 )
 
 func TestAgent_Self(t *testing.T) {
@@ -558,6 +559,29 @@ func TestAgent_ForceLeave(t *testing.T) {
 	}
 }
 
+func TestAgent_Monitor(t *testing.T) {
+	t.Parallel()
+	c, s := makeClient(t)
+	defer s.Stop()
+
+	agent := c.Agent()
+
+	logCh, err := agent.Monitor("info", nil)
+	if err != nil {
+		t.Fatalf("err: %v", err)
+	}
+
+	// Wait for the first log message and validate it
+	select {
+	case log := <-logCh:
+		if !strings.Contains(log, "[INFO] raft: Initial configuration") {
+			t.Fatalf("bad: %q", log)
+		}
+	case <-time.After(10 * time.Second):
+		t.Fatalf("failed to get a log message")
+	}
+}
+
 func TestServiceMaintenance(t *testing.T) {
 	t.Parallel()
 	c, s := makeClient(t)

command/agent/agent.go

@@ -19,6 +19,7 @@ import (
 	"github.com/hashicorp/consul/consul/state"
 	"github.com/hashicorp/consul/consul/structs"
 	"github.com/hashicorp/consul/lib"
+	"github.com/hashicorp/consul/logger"
 	"github.com/hashicorp/consul/types"
 	"github.com/hashicorp/go-uuid"
 	"github.com/hashicorp/serf/coordinate"
@@ -66,6 +67,9 @@ type Agent struct {
 	// Output sink for logs
 	logOutput io.Writer
 
+	// Used for streaming logs to
+	logWriter *logger.LogWriter
+
 	// We have one of a client or a server, depending
 	// on our configuration
 	server *consul.Server

command/agent/agent_endpoint.go

@@ -2,12 +2,15 @@ package agent
 
 import (
 	"fmt"
+	"log"
 	"net/http"
 	"strconv"
 	"strings"
 
 	"github.com/hashicorp/consul/consul/structs"
+	"github.com/hashicorp/consul/logger"
 	"github.com/hashicorp/consul/types"
+	"github.com/hashicorp/logutils"
 	"github.com/hashicorp/serf/coordinate"
 	"github.com/hashicorp/serf/serf"
 )
@@ -393,6 +396,61 @@ func (s *HTTPServer) AgentNodeMaintenance(resp http.ResponseWriter, req *http.Re
 	return nil, nil
 }
 
+func (s *HTTPServer) AgentMonitor(resp http.ResponseWriter, req *http.Request) (interface{}, error) {
+	// Only GET supported
+	if req.Method != "GET" {
+		resp.WriteHeader(405)
+		return nil, nil
+	}
+
+	// Get the provided loglevel
+	logLevel := req.URL.Query().Get("loglevel")
+	if logLevel == "" {
+		logLevel = "INFO"
+	}
+
+	// Upper case the log level
+	logLevel = strings.ToUpper(logLevel)
+
+	// Create a level filter
+	filter := logger.LevelFilter()
+	filter.MinLevel = logutils.LogLevel(logLevel)
+	if !logger.ValidateLevelFilter(filter.MinLevel, filter) {
+		resp.WriteHeader(400)
+		resp.Write([]byte(fmt.Sprintf("Unknown log level: %s", filter.MinLevel)))
+		return nil, nil
+	}
+
+	flusher, ok := resp.(http.Flusher)
+	if !ok {
+		return nil, fmt.Errorf("Streaming not supported")
+	}
+
+	// Set up a log handler
+	handler := &httpLogHandler{
+		filter: filter,
+		logCh:  make(chan string, 512),
+		logger: s.logger,
+	}
+	s.agent.logWriter.RegisterHandler(handler)
+	defer s.agent.logWriter.DeregisterHandler(handler)
+
+	notify := resp.(http.CloseNotifier).CloseNotify()
+
+	// Stream logs until the connection is closed
+	for {
+		select {
+		case <-notify:
+			return nil, nil
+		case log := <-handler.logCh:
+			resp.Write([]byte(log + "\n"))
+			flusher.Flush()
+		}
+	}
+
+	return nil, nil
+}
+
 // syncChanges is a helper function which wraps a blocking call to sync
 // services and checks to the server. If the operation fails, we only
 // only warn because the write did succeed and anti-entropy will sync later.
@@ -401,3 +459,27 @@ func (s *HTTPServer) syncChanges() {
 		s.logger.Printf("[ERR] agent: failed to sync changes: %v", err)
 	}
 }
+
+type httpLogHandler struct {
+	filter *logutils.LevelFilter
+	logCh  chan string
+	logger *log.Logger
+}
+
+func (h *httpLogHandler) HandleLog(log string) {
+	// Check the log level
+	if !h.filter.Check([]byte(log)) {
+		return
+	}
+
+	// Do a non-blocking send
+	select {
+	case h.logCh <- log:
+	default:
+		// We can't log synchronously, since we are already being invoked
+		// from the logWriter, and a log will need to invoke Write() which
+		// already holds the lock. We must therefor do the log async, so
+		// as to not deadlock
+		go h.logger.Printf("[WARN] Dropping logs to monitor http endpoint")
+	}
+}

command/agent/agent_endpoint_test.go

@@ -1,8 +1,10 @@
 package agent
 
 import (
+	"bytes"
 	"errors"
 	"fmt"
+	"io"
 	"net/http"
 	"net/http/httptest"
 	"os"
@@ -12,6 +14,7 @@ import (
 	"time"
 
 	"github.com/hashicorp/consul/consul/structs"
+	"github.com/hashicorp/consul/logger"
 	"github.com/hashicorp/consul/testutil"
 	"github.com/hashicorp/consul/types"
 	"github.com/hashicorp/serf/serf"
@@ -1019,3 +1022,69 @@ func TestHTTPAgentRegisterServiceCheck(t *testing.T) {
 		t.Fatalf("bad: %#v", result["memcached_check2"])
 	}
 }
+
+func TestHTTPAgent_Monitor(t *testing.T) {
+	logWriter := logger.NewLogWriter(512)
+	expectedLogs := bytes.Buffer{}
+	logger := io.MultiWriter(os.Stdout, &expectedLogs, logWriter)
+
+	dir, srv := makeHTTPServerWithConfigLog(t, nil, logger)
+	srv.agent.logWriter = logWriter
+	defer os.RemoveAll(dir)
+	defer srv.Shutdown()
+	defer srv.agent.Shutdown()
+
+	// Begin streaming logs from the monitor endpoint
+	req, _ := http.NewRequest("GET", "/v1/agent/monitor?loglevel=debug", nil)
+	resp := newClosableRecorder()
+	go func() {
+		if _, err := srv.AgentMonitor(resp, req); err != nil {
+			t.Fatalf("err: %s", err)
+		}
+	}()
+
+	// Write the incoming logs to a channel for reading
+	logCh := make(chan string, 0)
+	go func() {
+		for {
+			line, err := resp.Body.ReadString('\n')
+			if err != nil && err != io.EOF {
+				t.Fatalf("err: %v", err)
+			}
+			if line != "" {
+				logCh <- line
+			}
+		}
+	}()
+
+	// Verify that the first 5 logs we get match the expected stream
+	for i := 0; i < 5; i++ {
+		select {
+		case log := <-logCh:
+			expected, err := expectedLogs.ReadString('\n')
+			if err != nil {
+				t.Fatalf("err: %v", err)
+			}
+			if log != expected {
+				t.Fatalf("bad: %q %q", expected, log)
+			}
+		case <-time.After(10 * time.Second):
+			t.Fatalf("failed to get log within timeout")
+		}
+	}
+}
+
+type closableRecorder struct {
+	*httptest.ResponseRecorder
+	closer chan bool
+}
+
+func newClosableRecorder() *closableRecorder {
+	r := httptest.NewRecorder()
+	closer := make(chan bool)
+	return &closableRecorder{r, closer}
+}
+
+func (r *closableRecorder) CloseNotify() <-chan bool {
+	return r.closer
+}

command/agent/command.go

@@ -471,6 +471,7 @@ func (c *Command) setupAgent(config *Config, logOutput io.Writer, logWriter *log
 		c.Ui.Error(fmt.Sprintf("Error starting agent: %s", err))
 		return err
 	}
+	agent.logWriter = logWriter
 	c.agent = agent
 
 	// Setup the RPC listener

command/agent/http.go

@@ -251,6 +251,7 @@ func (s *HTTPServer) registerHandlers(enableDebug bool) {
 	}
 	s.handleFuncMetrics("/v1/agent/self", s.wrap(s.AgentSelf))
 	s.handleFuncMetrics("/v1/agent/maintenance", s.wrap(s.AgentNodeMaintenance))
+	s.handleFuncMetrics("/v1/agent/monitor", s.wrap(s.AgentMonitor))
 	s.handleFuncMetrics("/v1/agent/services", s.wrap(s.AgentServices))
 	s.handleFuncMetrics("/v1/agent/checks", s.wrap(s.AgentChecks))
 	s.handleFuncMetrics("/v1/agent/members", s.wrap(s.AgentMembers))

command/agent/http_test.go

@@ -28,6 +28,10 @@ func makeHTTPServer(t *testing.T) (string, *HTTPServer) {
 }
 
 func makeHTTPServerWithConfig(t *testing.T, cb func(c *Config)) (string, *HTTPServer) {
+	return makeHTTPServerWithConfigLog(t, cb, nil)
+}
+
+func makeHTTPServerWithConfigLog(t *testing.T, cb func(c *Config), l io.Writer) (string, *HTTPServer) {
 	configTry := 0
 RECONF:
 	configTry += 1
@@ -36,7 +40,7 @@ RECONF:
 		cb(conf)
 	}
 
-	dir, agent := makeAgent(t, conf)
+	dir, agent := makeAgentLog(t, conf, l)
 	servers, err := NewHTTPServers(agent, conf, agent.logOutput)
 	if err != nil {
 		if configTry < 3 {

website/source/docs/agent/http/agent.html.markdown

@@ -21,6 +21,7 @@ The following endpoints are supported:
 * [`/v1/agent/members`](#agent_members) : Returns the members as seen by the local serf agent
 * [`/v1/agent/self`](#agent_self) : Returns the local node configuration
 * [`/v1/agent/maintenance`](#agent_maintenance) : Manages node maintenance mode
+* [`/v1/agent/monitor`](#agent_monitor) : Streams logs from the local agent
 * [`/v1/agent/join/<address>`](#agent_join) : Triggers the local agent to join a node
 * [`/v1/agent/force-leave/<node>`](#agent_force_leave): Forces removal of a node
 * [`/v1/agent/check/register`](#agent_check_register) : Registers a new local check
@@ -211,6 +212,17 @@ to aid human operators. If no reason is provided, a default value will be used i
 
 The return code is 200 on success.
 
+### <a name="agent_monitor"></a> /v1/agent/monitor
+
+Added in Consul 0.7.2, This endpoint is hit with a GET and will stream logs from the
+local agent until the connection is closed.
+
+The `?loglevel` flag is optional.  If provided, its value should be a text string
+containing a log level to filter on, such as `info`. If no loglevel is provided, 
+`info` will be used as a default.
+
+The return code is 200 on success.
+
 ### <a name="agent_join"></a> /v1/agent/join/\<address\>
 
 This endpoint is hit with a GET and is used to instruct the agent to attempt to
@@ -403,7 +415,7 @@ body must look like:
   ],
   "Address": "127.0.0.1",
   "Port": 8000,
-  "EnableTagOverride": false, 
+  "EnableTagOverride": false,
   "Check": {
     "DeregisterCriticalServiceAfter": "90m",
     "Script": "/usr/local/bin/check_redis.py",