api: New API with health endpoint

api/api.go

@@ -0,0 +1,57 @@
+package api
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"net/http"
+
+	log "github.com/sirupsen/logrus"
+
+	"github.com/algorand/conduit/conduit/pipeline"
+)
+
+// StatusProvider is a subset of the Pipeline interface required by the health handler.
+type StatusProvider interface {
+	Status() (pipeline.Status, error)
+}
+
+func makeHealthHandler(p StatusProvider) func(w http.ResponseWriter, r *http.Request) {
+	return func(w http.ResponseWriter, r *http.Request) {
+		status, err := p.Status()
+		if err != nil {
+			w.WriteHeader(http.StatusInternalServerError)
+			fmt.Fprintf(w, `{"error": "%s"}`, err)
+			return
+		}
+		w.WriteHeader(http.StatusOK)
+		data, _ := json.Marshal(status)
+		fmt.Fprint(w, string(data))
+	}
+}
+
+// StartServer starts a http server that exposes a health check endpoint.
+// A callback is returned that can be used to gracefully shutdown the server.
+func StartServer(logger *log.Logger, p StatusProvider, address string) (func(ctx context.Context), error) {
+	mux := http.NewServeMux()
+	mux.HandleFunc("/health", makeHealthHandler(p))
+
+	srv := &http.Server{
+		Addr:    address,
+		Handler: mux,
+	}
+
+	go func() {
+		if err := srv.ListenAndServe(); err != nil && !errors.Is(err, http.ErrServerClosed) {
+			logger.Fatalf("failed to start API server: %s", err)
+		}
+	}()
+
+	shutdownCallback := func(ctx context.Context) {
+		if err := srv.Shutdown(ctx); err != nil {
+			logger.Fatalf("failed to shutdown API server: %s", err)
+		}
+	}
+	return shutdownCallback, nil
+}

api/api_test.go

@@ -0,0 +1,103 @@
+package api
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"net"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+	"time"
+
+	"github.com/sirupsen/logrus"
+	"github.com/sirupsen/logrus/hooks/test"
+	"github.com/stretchr/testify/require"
+
+	"github.com/algorand/conduit/conduit/pipeline"
+)
+
+type mockStatusProvider struct {
+	s   pipeline.Status
+	err error
+}
+
+func (m mockStatusProvider) Status() (pipeline.Status, error) {
+	if m.err != nil {
+		return pipeline.Status{}, m.err
+	}
+	return m.s, nil
+}
+
+func TestStartServer_BadAddress(t *testing.T) {
+	l, h := test.NewNullLogger()
+	// capture the fatal log if any.
+	l.ExitFunc = func(int) {}
+	sp := mockStatusProvider{}
+
+	shutdown, err := StartServer(l, sp, "bad address")
+	defer shutdown(context.Background())
+	require.NoError(t, err)
+	time.Sleep(1 * time.Millisecond)
+
+	require.Len(t, h.Entries, 1)
+	require.Equal(t, h.LastEntry().Level, logrus.FatalLevel)
+}
+
+func TestStartServer_GracefulShutdown(t *testing.T) {
+	l, h := test.NewNullLogger()
+	// capture the fatal log if any.
+	l.ExitFunc = func(int) {}
+	sp := mockStatusProvider{}
+	shutdown, err := StartServer(l, sp, "bad address")
+	defer shutdown(context.Background())
+	require.NoError(t, err)
+	require.Len(t, h.Entries, 0)
+}
+
+func TestStartServer_HealthCheck(t *testing.T) {
+	l, _ := test.NewNullLogger()
+	// capture the fatal log if any.
+	l.ExitFunc = func(int) {}
+	sp := mockStatusProvider{
+		s: pipeline.Status{
+			Round: 999,
+		},
+	}
+
+	// Find an open port...
+	listener, err := net.Listen("tcp", ":0")
+	addr := listener.Addr().String()
+	listener.Close()
+	require.NoError(t, err)
+
+	// Start server.
+	shutdown, err := StartServer(l, sp, addr)
+	defer shutdown(context.Background())
+	require.NoError(t, err)
+
+	// Make request.
+	resp, err := http.Get("http://" + addr + "/health")
+	require.NoError(t, err)
+
+	// Make sure we got the right response.
+	require.Equal(t, http.StatusOK, resp.StatusCode)
+	var respStatus pipeline.Status
+	json.NewDecoder(resp.Body).Decode(&respStatus)
+	require.NoError(t, err)
+	require.Equal(t, sp.s, respStatus)
+}
+
+func TestHealthHandlerError(t *testing.T) {
+	sp := mockStatusProvider{
+		err: fmt.Errorf("some error"),
+	}
+	handler := makeHealthHandler(sp)
+	rec := httptest.NewRecorder()
+	handler(rec, nil)
+
+	// validate response
+	resp := rec.Result()
+	require.Equal(t, http.StatusInternalServerError, resp.StatusCode)
+	require.Contains(t, rec.Body.String(), "some error")
+}

conduit/data/config.go

@@ -56,6 +56,11 @@ type Telemetry struct {
 	Password string `yaml:"password"`
 }
 
+// API defines parameters for the Conduit API server.
+type API struct {
+	Address string `yaml:"addr"`
+}
+
 // Config stores configuration specific to the conduit pipeline
 type Config struct {
 	// ConduitArgs are the program inputs. Should not be serialized for config.
@@ -72,6 +77,7 @@ type Config struct {
 	Processors []NameConfigPair `yaml:"processors"`
 	Exporter   NameConfigPair   `yaml:"exporter"`
 	Metrics    Metrics          `yaml:"metrics"`
+	API        API              `yaml:"api"`
 	// RetryCount is the number of retries to perform for an error in the pipeline
 	RetryCount uint64 `yaml:"retry-count"`
 	// RetryDelay is a duration amount interpreted from a string

conduit/pipeline/pipeline.go

@@ -9,6 +9,7 @@ import (
 	"path"
 	"runtime/pprof"
 	"sync"
+	"sync/atomic"
 	"time"
 
 	"github.com/prometheus/client_golang/prometheus"
@@ -37,6 +38,12 @@ type Pipeline interface {
 	Stop()
 	Error() error
 	Wait()
+	Status() (Status, error)
+}
+
+// Status is a struct that contains the current pipeline status.
+type Status struct {
+	Round uint64 `json:"round"`
 }
 
 type pipelineImpl struct {
@@ -532,6 +539,13 @@ func (p *pipelineImpl) Wait() {
 	p.wg.Wait()
 }
 
+func (p *pipelineImpl) Status() (Status, error) {
+	rnd := atomic.LoadUint64(&p.pipelineMetadata.NextRound)
+	return Status{
+		Round: rnd,
+	}, nil
+}
+
 // start a http server serving /metrics
 func (p *pipelineImpl) startMetricsServer() {
 	http.Handle("/metrics", promhttp.Handler())

pkg/cli/cli.go

@@ -10,6 +10,7 @@ import (
 	log "github.com/sirupsen/logrus"
 	"github.com/spf13/cobra"
 
+	"github.com/algorand/conduit/api"
 	"github.com/algorand/conduit/conduit/data"
 	"github.com/algorand/conduit/conduit/loggers"
 	"github.com/algorand/conduit/conduit/pipeline"
@@ -101,6 +102,20 @@ func runConduitCmdWithConfig(args *data.Args) error {
 	}
 	pipeline.Start()
 	defer pipeline.Stop()
+
+	// Start server
+	if pCfg.API.Address != "" {
+		shutdown, err := api.StartServer(logger, pipeline, pCfg.API.Address)
+		if err != nil {
+			// Suppress log, it is about to be printed to stderr.
+			if pCfg.LogFile != "" {
+				logger.Error(err)
+			}
+			return fmt.Errorf("failed to start API server: %w", err)
+		}
+		defer shutdown(context.Background())
+	}
+
 	pipeline.Wait()
 	return pipeline.Error()
 }

pkg/cli/internal/initialize/conduit.yml.example

@@ -17,6 +17,10 @@ retry-delay: "1s"
 # Whether or not to print the conduit banner on startup.
 hide-banner: false
 
+# When the address is not empty information is available on '/health'
+api:
+    addr: ":8981"
+
 # When enabled prometheus metrics are available on '/metrics'
 metrics:
     mode: OFF
@@ -33,14 +37,3 @@ processors:
 # An exporter is defined to do something with the data.
 exporter:
 %s
-
-# Enable telemetry for conduit
-telemetry:
-  enabled: false
-
-  # By default the following fields will be configured to send data to Algorand.
-  # To store your own telemetry events, they can be overridden.
-  # uri: ""
-  # index: ""
-  # username: ""
-  # password: ""