Implement HTTP Watch handler (#3413)

Implement HTTP Watch handler

agent/agent.go

@@ -534,7 +534,13 @@ func (a *Agent) reloadWatches(cfg *config.RuntimeConfig) error {
 	// Compile the watches
 	var watchPlans []*watch.Plan
 	for _, params := range cfg.Watches {
-		// Parse the watches, excluding the handler
+		if handlerType, ok := params["handler_type"]; !ok {
+			params["handler_type"] = "script"
+		} else if handlerType != "http" && handlerType != "script" {
+			return fmt.Errorf("Handler type '%s' not recognized", params["handler_type"])
+		}
+
+		// Parse the watches, excluding 'handler' and 'args'
 		wp, err := watch.ParseExempt(params, []string{"handler", "args"})
 		if err != nil {
 			return fmt.Errorf("Failed to parse watch (%#v): %v", params, err)
@@ -563,11 +569,11 @@ func (a *Agent) reloadWatches(cfg *config.RuntimeConfig) error {
 		} else if hasArgs && !ok {
 			return fmt.Errorf("Watch args must be a list of strings")
 		}
-		if hasHandler && hasArgs {
+		if hasHandler && hasArgs || hasHandler && wp.HandlerType == "http" || hasArgs && wp.HandlerType == "http" {
-			return fmt.Errorf("Cannot define both watch handler and args")
+			return fmt.Errorf("Only one watch handler allowed")
 		}
-		if !hasHandler && !hasArgs {
+		if !hasHandler && !hasArgs && wp.HandlerType != "http" {
-			return fmt.Errorf("Must define either watch handler or args")
+			return fmt.Errorf("Must define a watch handler")
 		}
 
 		// Store the watch plan
@@ -590,13 +596,14 @@ func (a *Agent) reloadWatches(cfg *config.RuntimeConfig) error {
 	for _, wp := range watchPlans {
 		a.watchPlans = append(a.watchPlans, wp)
 		go func(wp *watch.Plan) {
-			var handler interface{}
 			if h, ok := wp.Exempt["handler"]; ok {
-				handler = h
+				wp.Handler = makeWatchHandler(a.LogOutput, h)
+			} else if h, ok := wp.Exempt["args"]; ok {
+				wp.Handler = makeWatchHandler(a.LogOutput, h)
 			} else {
-				handler = wp.Exempt["args"]
+				httpConfig := wp.Exempt["http_handler_config"].(*watch.HttpHandlerConfig)
+				wp.Handler = makeHTTPWatchHandler(a.LogOutput, httpConfig)
 			}
-			wp.Handler = makeWatchHandler(a.LogOutput, handler)
 			wp.LogOutput = a.LogOutput
 			if err := wp.Run(addr); err != nil {
 				a.logger.Printf("[ERR] Failed to run watch: %v", err)

agent/watch_handler.go

@@ -10,8 +10,12 @@ import (
 	"os/exec"
 	"strconv"
 
+	"crypto/tls"
 	"github.com/armon/circbuf"
 	"github.com/hashicorp/consul/watch"
+	"github.com/hashicorp/go-cleanhttp"
+	"golang.org/x/net/context"
+	"net/http"
 )
 
 const (
@@ -87,3 +91,77 @@ func makeWatchHandler(logOutput io.Writer, handler interface{}) watch.HandlerFun
 	}
 	return fn
 }
+
+func makeHTTPWatchHandler(logOutput io.Writer, config *watch.HttpHandlerConfig) watch.HandlerFunc {
+	logger := log.New(logOutput, "", log.LstdFlags)
+
+	fn := func(idx uint64, data interface{}) {
+		trans := cleanhttp.DefaultTransport()
+
+		// Skip SSL certificate verification if TLSSkipVerify is true
+		if trans.TLSClientConfig == nil {
+			trans.TLSClientConfig = &tls.Config{
+				InsecureSkipVerify: config.TLSSkipVerify,
+			}
+		} else {
+			trans.TLSClientConfig.InsecureSkipVerify = config.TLSSkipVerify
+		}
+
+		ctx := context.Background()
+		ctx, cancel := context.WithTimeout(ctx, config.Timeout)
+		defer cancel()
+
+		// Create the HTTP client.
+		httpClient := &http.Client{
+			Transport: trans,
+		}
+
+		// Setup the input
+		var inp bytes.Buffer
+		enc := json.NewEncoder(&inp)
+		if err := enc.Encode(data); err != nil {
+			logger.Printf("[ERR] agent: Failed to encode data for http watch '%s': %v", config.Path, err)
+			return
+		}
+
+		req, err := http.NewRequest(config.Method, config.Path, &inp)
+		if err != nil {
+			logger.Printf("[ERR] agent: Failed to setup http watch: %v", err)
+			return
+		}
+		req = req.WithContext(ctx)
+		req.Header.Add("Content-Type", "application/json")
+		req.Header.Add("X-Consul-Index", strconv.FormatUint(idx, 10))
+		for key, values := range config.Header {
+			for _, val := range values {
+				req.Header.Add(key, val)
+			}
+		}
+		resp, err := httpClient.Do(req)
+		if err != nil {
+			logger.Printf("[ERR] agent: Failed to invoke http watch handler '%s': %v", config.Path, err)
+			return
+		}
+		defer resp.Body.Close()
+
+		// Collect the output
+		output, _ := circbuf.NewBuffer(WatchBufSize)
+		io.Copy(output, resp.Body)
+
+		// Get the output, add a message about truncation
+		outputStr := string(output.Bytes())
+		if output.TotalWritten() > output.Size() {
+			outputStr = fmt.Sprintf("Captured %d of %d bytes\n...\n%s",
+				output.Size(), output.TotalWritten(), outputStr)
+		}
+
+		if resp.StatusCode >= 200 && resp.StatusCode <= 299 {
+			// Log the output
+			logger.Printf("[TRACE] agent: http watch handler '%s' output: %s", config.Path, outputStr)
+		} else {
+			logger.Printf("[ERR] agent: http watch handler '%s' got '%s' with output: %s",
+				config.Path, resp.Status, outputStr)
+		}
+	}
+	return fn
+}

agent/watch_handler_test.go

@@ -1,9 +1,13 @@
 package agent
 
 import (
+	"github.com/hashicorp/consul/watch"
 	"io/ioutil"
+	"net/http"
+	"net/http/httptest"
 	"os"
 	"testing"
+	"time"
 )
 
 func TestMakeWatchHandler(t *testing.T) {
@@ -28,3 +32,34 @@ func TestMakeWatchHandler(t *testing.T) {
 		t.Fatalf("bad: %s", raw)
 	}
 }
+
+func TestMakeHTTPWatchHandler(t *testing.T) {
+	t.Parallel()
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		idx := r.Header.Get("X-Consul-Index")
+		if idx != "100" {
+			t.Fatalf("bad: %s", idx)
+		}
+		// Get the first one
+		customHeader := r.Header.Get("X-Custom")
+		if customHeader != "abc" {
+			t.Fatalf("bad: %s", idx)
+		}
+		body, err := ioutil.ReadAll(r.Body)
+		if err != nil {
+			t.Fatalf("err: %v", err)
+		}
+		if string(body) != "[\"foo\",\"bar\",\"baz\"]\n" {
+			t.Fatalf("bad: %s", body)
+		}
+		w.Write([]byte("Ok, i see"))
+	}))
+	defer server.Close()
+	config := watch.HttpHandlerConfig{
+		Path:    server.URL,
+		Header:  map[string][]string{"X-Custom": {"abc", "def"}},
+		Timeout: time.Minute,
+	}
+	handler := makeHTTPWatchHandler(os.Stderr, &config)
+	handler(100, []string{"foo", "bar", "baz"})
+}

watch/watch.go

@@ -7,8 +7,12 @@ import (
 	"sync"
 
 	consulapi "github.com/hashicorp/consul/api"
+	"github.com/mitchellh/mapstructure"
+	"time"
 )
 
+const DefaultTimeout = 10 * time.Second
+
 // Plan is the parsed version of a watch specification. A watch provides
 // the details of a query, which generates a view into the Consul data store.
 // This view is watched for changes and a handler is invoked to take any
@@ -17,6 +21,7 @@ type Plan struct {
 	Datacenter  string
 	Token       string
 	Type        string
+	HandlerType string
 	Exempt      map[string]interface{}
 
 	Watcher   WatcherFunc
@@ -34,6 +39,15 @@ type Plan struct {
 	cancelFunc context.CancelFunc
 }
 
+type HttpHandlerConfig struct {
+	Path          string              `mapstructure:"path"`
+	Method        string              `mapstructure:"method"`
+	Timeout       time.Duration       `mapstructure:"-"`
+	TimeoutRaw    string              `mapstructure:"timeout"`
+	Header        map[string][]string `mapstructure:"header"`
+	TLSSkipVerify bool                `mapstructure:"tls_skip_verify"`
+}
+
 // WatcherFunc is used to watch for a diff
 type WatcherFunc func(*Plan) (uint64, interface{}, error)
 
@@ -50,6 +64,7 @@ func Parse(params map[string]interface{}) (*Plan, error) {
 func ParseExempt(params map[string]interface{}, exempt []string) (*Plan, error) {
 	plan := &Plan{
 		stopCh: make(chan struct{}),
+		Exempt: make(map[string]interface{}),
 	}
 
 	// Parse the generic parameters
@@ -62,12 +77,31 @@ func ParseExempt(params map[string]interface{}, exempt []string) (*Plan, error)
 	if err := assignValue(params, "type", &plan.Type); err != nil {
 		return nil, err
 	}
-
 	// Ensure there is a watch type
 	if plan.Type == "" {
 		return nil, fmt.Errorf("Watch type must be specified")
 	}
 
+	// Get the specific handler
+	if err := assignValue(params, "handler_type", &plan.HandlerType); err != nil {
+		return nil, err
+	}
+	switch plan.HandlerType {
+	case "http":
+		if _, ok := params["http_handler_config"]; !ok {
+			return nil, fmt.Errorf("Handler type 'http' requires 'http_handler_config' to be set")
+		}
+		config, err := parseHttpHandlerConfig(params["http_handler_config"])
+		if err != nil {
+			return nil, fmt.Errorf(fmt.Sprintf("Failed to parse 'http_handler_config': %v", err))
+		}
+		plan.Exempt["http_handler_config"] = config
+		delete(params, "http_handler_config")
+
+	case "script":
+		// Let the caller check for configuration in exempt parameters
+	}
+
 	// Look for a factory function
 	factory := watchFuncFactory[plan.Type]
 	if factory == nil {
@@ -83,7 +117,6 @@ func ParseExempt(params map[string]interface{}, exempt []string) (*Plan, error)
 
 	// Remove the exempt parameters
 	if len(exempt) > 0 {
-		plan.Exempt = make(map[string]interface{})
 		for _, ex := range exempt {
 			val, ok := params[ex]
 			if ok {
@@ -129,3 +162,27 @@ func assignValueBool(params map[string]interface{}, name string, out *bool) erro
 	}
 	return nil
 }
+
+// Parse the 'http_handler_config' parameters
+func parseHttpHandlerConfig(configParams interface{}) (*HttpHandlerConfig, error) {
+	var config HttpHandlerConfig
+	if err := mapstructure.Decode(configParams, &config); err != nil {
+		return nil, err
+	}
+
+	if config.Path == "" {
+		return nil, fmt.Errorf("Requires 'path' to be set")
+	}
+	if config.Method == "" {
+		config.Method = "POST"
+	}
+	if config.TimeoutRaw == "" {
+		config.Timeout = DefaultTimeout
+	} else if timeout, err := time.ParseDuration(config.TimeoutRaw); err != nil {
+		return nil, fmt.Errorf(fmt.Sprintf("Failed to parse timeout: %v", err))
+	} else {
+		config.Timeout = timeout
+	}
+
+	return &config, nil
+}

website/source/docs/agent/watches.html.md

@@ -10,7 +10,7 @@ description: |-
 
 Watches are a way of specifying a view of data (e.g. list of nodes, KV pairs, health
 checks) which is monitored for updates. When an update is detected, an external handler
-is invoked. A handler can be any executable. As an example, you could watch the status
+is invoked. A handler can be any executable or HTTP endpoint. As an example, you could watch the status
 of health checks and notify an external system when a check is critical.
 
 Watches are implemented using blocking queries in the [HTTP API](/api/index.html).
@@ -32,24 +32,67 @@ in a JSON body when using agent configuration or as CLI flags for the watch comm
 ## Handlers
 
 The watch configuration specifies the view of data to be monitored.
-Once that view is updated, the specified handler is invoked. The handler
+Once that view is updated, the specified handler is invoked. Supported handlers
-can be any executable.
+are any executable or HTTP endpoint. A handler receives JSON formatted data
-
+with invocation info, following a format that depends on the type of the watch.
-A handler should read its input from stdin and expect to read
+Each watch type documents the format type. Because they map directly to an HTTP
-JSON formatted data. The format of the data depends on the type of the
+API, handlers should expect the input to match the format of the API. A Consul
-watch. Each watch type documents the format type. Because they
+index is also given, corresponding to the responses from the
-map directly to an HTTP API, handlers should expect the input to
-match the format of the API.
-
-Additionally, the `CONSUL_INDEX` environment variable will be set.
-This maps to the `X-Consul-Index` value in responses from the
 [HTTP API](/api/index.html). 
 
+### Executable
+
+An executable handler reads the JSON invocation info from stdin. Additionally,
+the `CONSUL_INDEX` environment variable will be set to the Consul index
+Anything written to stdout is logged.
+
+Here is an example configuration, where `handler_type` is optionally set to
+`script`:
+
+```javascript
+{
+  "type": "key",
+  "key": "foo/bar/baz",
+  "handler_type": "script",
+  "args": ["/usr/bin/my-service-handler.sh", "-redis"]
+}
+```
+
 Prior to Consul 1.0, watches used a single `handler` field to define the command to run, and
 would always run in a shell. In Consul 1.0, the `args` array was added so that handlers can be
 run without a shell. The `handler` field is deprecated, and you should include the shell in
 the `args` to run under a shell, eg. `"args": ["sh", "-c", "..."]`.
 
+### HTTP endpoint
+
+A HTTP handler sends a HTTP request when a watch is invoked. The JSON
+invocation info is sent as a payload along the request. Consul index is sent in
+the header `X-Consul-Index`. Any response is logged.
+
+The HTTP handler can be configured by setting `handler_type` to `http`. The
+`http_handler_config` map must provide a `path` field with a URL to the HTTP
+endpoint. HTTP method is `POST` as a default, but can be set to any method.
+Though a JSON payload is sent in all cases. The `header`, `timeout` and
+`tls_skip_verify` field is also optional and configured the same way as in
+[HTTP checks](/docs/agent/checks.html).
+
+Here is an example configuration:
+
+```javascript
+{
+  "type": "key",
+  "key": "foo/bar/baz",
+  "handler_type": "http",
+  "http_handler_config": {
+    "path":"https://localhost:8000/watch",
+    "method": "POST",
+    "header": {"x-foo":["bar", "baz"]},
+    "timeout": "10s",
+    "tls_skip_verify": false
+  }
+}
+```
+
 ## Global Parameters
 
 In addition to the parameters supported by each option type, there