Support email plugin status sink

integrations/access/email/app.go

@@ -123,6 +123,7 @@ func (a *App) run(ctx context.Context) error {
 
 // init inits plugin
 func (a *App) init(ctx context.Context) error {
+	log := logger.Get(ctx)
 	ctx, cancel := context.WithTimeout(ctx, initTimeout)
 	defer cancel()
 
@@ -146,6 +147,11 @@ func (a *App) init(ctx context.Context) error {
 		return trace.Wrap(err)
 	}
 
+	log.Debug("Starting client connection health check...")
+	if err = a.client.CheckHealth(ctx); err != nil {
+		return trace.Wrap(err, "client connection health check failed")
+	}
+	log.Debug("Client connection health check finished ok")
 	return nil
 }
 

integrations/access/email/client.go

@@ -59,12 +59,12 @@ func NewClient(ctx context.Context, conf Config, clusterName, webProxyAddr strin
 	}
 
 	if conf.Mailgun != nil {
-		mailer = NewMailgunMailer(*conf.Mailgun, conf.Delivery.Sender, clusterName)
+		mailer = NewMailgunMailer(*conf.Mailgun, conf.StatusSink, conf.Delivery.Sender, clusterName, conf.RoleToRecipients[types.Wildcard])
 		logger.Get(ctx).WithField("domain", conf.Mailgun.Domain).Info("Using Mailgun as email transport")
 	}
 
 	if conf.SMTP != nil {
-		mailer = NewSMTPMailer(*conf.SMTP, conf.Delivery.Sender, clusterName)
+		mailer = NewSMTPMailer(*conf.SMTP, conf.StatusSink, conf.Delivery.Sender, clusterName)
 		logger.Get(ctx).WithFields(logger.Fields{
 			"host":     conf.SMTP.Host,
 			"port":     conf.SMTP.Port,
@@ -79,6 +79,11 @@ func NewClient(ctx context.Context, conf Config, clusterName, webProxyAddr strin
 	}, nil
 }
 
+// CheckHealth checks if the Email client connection is healthy.
+func (c *Client) CheckHealth(ctx context.Context) error {
+	return trace.Wrap(c.mailer.CheckHealth(ctx))
+}
+
 // SendNewThreads sends emails on new requests. Returns EmailData.
 func (c *Client) SendNewThreads(ctx context.Context, recipients []string, reqID string, reqData RequestData) ([]EmailThread, error) {
 	var threads []EmailThread

integrations/access/email/config.go

@@ -64,6 +64,10 @@ type Config struct {
 	Delivery         DeliveryConfig          `toml:"delivery"`
 	RoleToRecipients common.RawRecipientsMap `toml:"role_to_recipients"`
 	Log              logger.Config           `toml:"log"`
+
+	// StatusSink receives any status updates from the plugin for
+	// further processing. Status updates will be ignored if not set.
+	StatusSink common.StatusSink
 }
 
 // LoadConfig reads the config file, initializes a new Config struct object, and returns it.

integrations/access/email/mailers.go

@@ -21,6 +21,7 @@ import (
 	"crypto/rand"
 	"encoding/binary"
 	"fmt"
+	"net/http"
 	"os"
 	"strconv"
 	"strings"
@@ -29,42 +30,85 @@ import (
 	"github.com/gravitational/trace"
 	"github.com/mailgun/mailgun-go/v4"
 	"gopkg.in/mail.v2"
+
+	"github.com/gravitational/teleport/integrations/access/common"
+	"github.com/gravitational/teleport/integrations/lib/logger"
+)
+
+const (
+	// statusEmitTimeout specifies the max timeout to emit status.
+	statusEmitTimeout = 10 * time.Second
+	// mailgunHTTPTimeout specifies the max timeout for mailgun api send request.
+	mailgunHTTPTimeout = 10 * time.Second
 )
 
 // Mailer is an interface to mail sender
 type Mailer interface {
 	Send(ctx context.Context, id, recipient, body, references string) (string, error)
+	// CheckHealth checks if the Email client connection is healthy.
+	CheckHealth(ctx context.Context) error
 }
 
 // SMTPMailer implements SMTP mailer
 type SMTPMailer struct {
 	dialer      *mail.Dialer
 	sender      string
 	clusterName string
+	sink        common.StatusSink
 }
 
 // MailgunMailer implements mailgun mailer
 type MailgunMailer struct {
 	mailgun     *mailgun.MailgunImpl
 	sender      string
 	clusterName string
+
+	// fallbackRecipients specifies the list of default recipients.
+	// This is only used for inital health check.
+	fallbackRecipients []string
 }
 
 // NewSMTPMailer inits new SMTP mailer
-func NewSMTPMailer(c SMTPConfig, sender, clusterName string) Mailer {
+func NewSMTPMailer(c SMTPConfig, sink common.StatusSink, sender, clusterName string) Mailer {
 	dialer := mail.NewDialer(c.Host, c.Port, c.Username, c.Password)
 	dialer.StartTLSPolicy = c.MailStartTLSPolicy
 
-	return &SMTPMailer{dialer, sender, clusterName}
+	return &SMTPMailer{dialer, sender, clusterName, sink}
 }
 
 // NewMailgunMailer inits new Mailgun mailer
-func NewMailgunMailer(c MailgunConfig, sender, clusterName string) Mailer {
+func NewMailgunMailer(c MailgunConfig, sink common.StatusSink, sender, clusterName string, fallbackRecipients []string) Mailer {
 	m := mailgun.NewMailgun(c.Domain, c.PrivateKey)
 	if c.APIBase != "" {
 		m.SetAPIBase(c.APIBase)
 	}
-	return &MailgunMailer{m, sender, clusterName}
+	client := &http.Client{
+		Transport: &statusSinkTransport{
+			RoundTripper: http.DefaultTransport,
+			sink:         sink,
+		},
+	}
+	m.SetClient(client)
+	return &MailgunMailer{
+		mailgun:            m,
+		sender:             sender,
+		clusterName:        clusterName,
+		fallbackRecipients: fallbackRecipients,
+	}
+}
+
+// CheckHealth checks the health of the SMTP service.
+func (m *SMTPMailer) CheckHealth(ctx context.Context) error {
+	log := logger.Get(ctx)
+	client, err := m.dialer.Dial()
+	m.emitStatus(ctx, err)
+	if err != nil {
+		return trace.Wrap(err)
+	}
+	if err := client.Close(); err != nil {
+		log.Debug("Failed to close client connection after health check")
+	}
+	return nil
 }
 
 // Send sends email via SMTP
@@ -91,10 +135,10 @@ func (m *SMTPMailer) Send(ctx context.Context, id, recipient, body, references s
 	}
 
 	err = m.dialer.DialAndSend(msg)
+	m.emitStatus(ctx, err)
 	if err != nil {
 		return "", trace.Wrap(err)
 	}
-
 	return id, nil
 }
 
@@ -123,6 +167,38 @@ func (m *SMTPMailer) base36(input uint64) string {
 	return strings.ToUpper(strconv.FormatUint(input, 36))
 }
 
+// emitStatus emits generic internal server error status.
+func (m *SMTPMailer) emitStatus(ctx context.Context, err error) {
+	if m.sink == nil {
+		return
+	}
+
+	ctx, cancel := context.WithTimeout(ctx, statusEmitTimeout)
+	defer cancel()
+
+	log := logger.Get(ctx)
+	code := http.StatusOK
+	if err != nil {
+		// Returned error is undocumented. Using geneirc error code for all errors.
+		code = http.StatusInternalServerError
+	}
+	if err := m.sink.Emit(ctx, common.StatusFromStatusCode(code)); err != nil {
+		log.WithError(err).Error("Error while emitting Email plugin status")
+	}
+}
+
+// CheckHealth checks the health of the Mailgun service.
+func (m *MailgunMailer) CheckHealth(ctx context.Context) error {
+	ctx, cancel := context.WithTimeout(ctx, mailgunHTTPTimeout)
+	defer cancel()
+
+	msg := m.mailgun.NewMessage(m.sender, "Health Check", "Testing Mailgun API connection...", m.fallbackRecipients...)
+	msg.SetRequireTLS(true)
+	msg.EnableTestMode() // Test message submission without delivering to recpients.
+	_, _, err := m.mailgun.Send(ctx, msg)
+	return trace.Wrap(err)
+}
+
 // Send sends email via Mailgun
 func (m *MailgunMailer) Send(ctx context.Context, id, recipient, body, references string) (string, error) {
 	subject := fmt.Sprintf("%v Role Request %v", m.clusterName, id)
@@ -136,7 +212,7 @@ func (m *MailgunMailer) Send(ctx context.Context, id, recipient, body, reference
 		msg.AddHeader("In-Reply-To", refHeader)
 	}
 
-	ctx, cancel := context.WithTimeout(ctx, time.Second*10)
+	ctx, cancel := context.WithTimeout(ctx, mailgunHTTPTimeout)
 	defer cancel()
 
 	_, id, err := m.mailgun.Send(ctx, msg)
@@ -147,3 +223,29 @@ func (m *MailgunMailer) Send(ctx context.Context, id, recipient, body, reference
 
 	return id, nil
 }
+
+// statusSinkTransport wraps the Mailgun client transport and
+// emits plugin status.
+type statusSinkTransport struct {
+	http.RoundTripper
+	sink common.StatusSink
+}
+
+// RoundTrip implements the http.RoundTripper interface.
+func (t *statusSinkTransport) RoundTrip(req *http.Request) (*http.Response, error) {
+	log := logger.Get(req.Context())
+	resp, err := t.RoundTripper.RoundTrip(req)
+	if err != nil {
+		return nil, trace.Wrap(err)
+	}
+	if t.sink != nil {
+		ctx, cancel := context.WithTimeout(req.Context(), statusEmitTimeout)
+		defer cancel()
+
+		status := common.StatusFromStatusCode(resp.StatusCode)
+		if err := t.sink.Emit(ctx, status); err != nil {
+			log.WithError(err).Error("Error while emitting Email plugin status")
+		}
+	}
+	return resp, nil
+}

integrations/access/email/testlib/mock_mailgun.go

@@ -63,6 +63,13 @@ func newMockMailgunServer(concurrency int) *mockMailgunServer {
 
 			id := uuid.New().String()
 
+			// The testmode flag is only used during health check.
+			// Do no create message when in testmode.
+			if r.PostFormValue("o:testmode") == "yes" {
+				fmt.Fprintf(w, `{"id": "%v"}`, id)
+				return
+			}
+
 			message := mockMailgunMessage{
 				ID:         id,
 				Sender:     r.PostFormValue("from"),