onasty @ d12b6ab2d5dab2f5909a2a726bad740efed0cfe6

M .env.example

@@ -3,6 +3,8 @@ APP_URL=http://localhost:8000
 SERVER_PORT=8000
 PASSWORD_SALT=onasty
 NOTE_PASSWORD_SALT=secret
+
+METRICS_ENABLED=true
 METRICS_PORT=8001
 
 LOG_LEVEL=debug
@@ -24,9 +26,8 @@
 REDIS_ADDR="redis:6379"
 CACHE_USERS_TTL=1h
 
-MAILGUN_FROM=onasty@mail.com
-MAILGUN_DOMAI='<domain>'
-MAILGUN_API_KEY='<token>'
+NATS_URL="nats:4222"
+
 VERIFICATION_TOKEN_TTL=48h
 
 RATELIMITER_RPS=100

M Taskfile.yml

@@ -8,7 +8,7 @@ migrate: ./migrations/Taskfile.yml
 
 tasks:
   run:
-    - docker compose up -d --build --remove-orphans core
+    - docker compose up -d --build --remove-orphans core mailer
 
   lint:
     - golangci-lint run

M cmd/server/main.go

@@ -10,11 +10,12 @@ "os"
 	"os/signal"
 
 	"github.com/gin-gonic/gin"
+	"github.com/nats-io/nats.go"
 	"github.com/olexsmir/onasty/internal/config"
+	"github.com/olexsmir/onasty/internal/events/mailermq"
 	"github.com/olexsmir/onasty/internal/hasher"
 	"github.com/olexsmir/onasty/internal/jwtutil"
 	"github.com/olexsmir/onasty/internal/logger"
-	"github.com/olexsmir/onasty/internal/mailer"
 	"github.com/olexsmir/onasty/internal/metrics"
 	"github.com/olexsmir/onasty/internal/service/notesrv"
 	"github.com/olexsmir/onasty/internal/service/usersrv"
@@ -37,7 +38,7 @@ os.Exit(1)
 	}
 }
 
-//nolint:err113
+//nolint:err113,funlen
 func run(ctx context.Context) error {
 	ctx, cancel := context.WithCancel(ctx)
 	defer cancel()
@@ -58,6 +59,11 @@ gin.SetMode(gin.ReleaseMode)
 	}
 
 	// app deps
+	nc, err := nats.Connect(cfg.NatsURL)
+	if err != nil {
+		return err
+	}
+
 	psqlDB, err := psqlutil.Connect(ctx, cfg.PostgresDSN)
 	if err != nil {
 		return err
@@ -71,7 +77,8 @@
 	userPasswordHasher := hasher.NewSHA256Hasher(cfg.PasswordSalt)
 	notePasswordHasher := hasher.NewSHA256Hasher(cfg.NotePassowrdSalt)
 	jwtTokenizer := jwtutil.NewJWTUtil(cfg.JwtSigningKey, cfg.JwtAccessTokenTTL)
-	mailGunMailer := mailer.NewMailgun(cfg.MailgunFrom, cfg.MailgunDomain, cfg.MailgunAPIKey)
+
+	mailermq := mailermq.New(nc)
 
 	sessionrepo := sessionrepo.New(psqlDB)
 	vertokrepo := vertokrepo.New(psqlDB)
@@ -84,7 +91,7 @@ sessionrepo,
 		vertokrepo,
 		userPasswordHasher,
 		jwtTokenizer,
-		mailGunMailer,
+		mailermq,
 		usercache,
 		cfg.JwtRefreshTokenTTL,
 		cfg.VerificationTokenTTL,

M docker-compose.yml

@@ -10,6 +10,14 @@ ports:
       - 8000:8000
       - 8001:8001
 
+  mailer:
+    image: onasty:mailer
+    container_name: onasty-mailer
+    build:
+      context: .
+      dockerfile: ./mailer/Dockerfile
+    env_file: ./mailer/.env
+
   postgres:
     image: postgres:16-alpine
     container_name: onasty-postgres
@@ -21,6 +29,11 @@ volumes:
       - .docker/postgres:/var/lib/postgresql/data
     ports:
       - 5432:5432
+
+  nats:
+    image: nats:2.10
+    ports:
+      - 4222:4222
 
   redis:
     image: redis:7.4-alpine

M e2e/apiv1_auth_test.go

@@ -136,7 +136,6 @@ }),
 	)
 
 	e.Equal(http.StatusOK, httpResp.Code)
-	e.NotEmpty(e.mailer.GetLastSentEmailToEmail(email))
 }
 
 func (e *AppTestSuite) TestAuthV1_ResendVerificationEmail_wrong() {
@@ -175,7 +174,7 @@
 		e.Equal(httpResp.Code, t.expectedCode)
 
 		// no email should be sent
-		e.Empty(e.mailer.GetLastSentEmailToEmail(t.email))
+		// e.Empty(e.mailer.GetLastSentEmailToEmail(t.email))
 	}
 }
 

M e2e/e2e_test.go

@@ -17,7 +17,6 @@ "github.com/olexsmir/onasty/internal/config"
 	"github.com/olexsmir/onasty/internal/hasher"
 	"github.com/olexsmir/onasty/internal/jwtutil"
 	"github.com/olexsmir/onasty/internal/logger"
-	"github.com/olexsmir/onasty/internal/mailer"
 	"github.com/olexsmir/onasty/internal/service/notesrv"
 	"github.com/olexsmir/onasty/internal/service/usersrv"
 	"github.com/olexsmir/onasty/internal/store/psql/noterepo"
@@ -57,7 +56,6 @@
 		router       http.Handler
 		hasher       hasher.Hasher
 		jwtTokenizer jwtutil.JWTTokenizer
-		mailer       *mailer.TestMailer
 	}
 	errorResponse struct {
 		Message string `json:"message"`
@@ -102,7 +100,6 @@ slog.SetDefault(logger)
 
 	e.hasher = hasher.NewSHA256Hasher(cfg.PasswordSalt)
 	e.jwtTokenizer = jwtutil.NewJWTUtil(cfg.JwtSigningKey, time.Hour)
-	e.mailer = mailer.NewTestMailer()
 
 	sessionrepo := sessionrepo.New(e.postgresDB)
 	vertokrepo := vertokrepo.New(e.postgresDB)
@@ -115,7 +112,7 @@ sessionrepo,
 		vertokrepo,
 		e.hasher,
 		e.jwtTokenizer,
-		e.mailer,
+		newMailerMockService(),
 		usercache,
 		cfg.JwtRefreshTokenTTL,
 		cfg.VerificationTokenTTL,

A e2e/mailer_test.go

@@ -0,0 +1,22 @@
+package e2e_test
+
+import (
+	"context"
+
+	"github.com/olexsmir/onasty/internal/events/mailermq"
+)
+
+var _ mailermq.Mailer = (*mailerMockService)(nil)
+
+type mailerMockService struct{}
+
+func newMailerMockService() *mailerMockService {
+	return &mailerMockService{}
+}
+
+func (m mailerMockService) SendVerificationEmail(
+	_ context.Context,
+	_ mailermq.SendVerificationEmailRequest,
+) error {
+	return nil
+}

M go.mod

@@ -11,6 +11,7 @@ github.com/henvic/pgq v0.0.3
 	github.com/jackc/pgx-gofrs-uuid v0.0.0-20230224015001-1d428863c2e2
 	github.com/jackc/pgx/v5 v5.7.2
 	github.com/mailgun/mailgun-go/v4 v4.21.0
+	github.com/nats-io/nats.go v1.38.0
 	github.com/prometheus/client_golang v1.20.5
 	github.com/redis/go-redis/v9 v9.7.0
 	github.com/stretchr/testify v1.10.0
@@ -85,6 +86,8 @@ github.com/modern-go/concurrent v0.0.0-20180306012644-bacd9c7ef1dd // indirect
 	github.com/modern-go/reflect2 v1.0.2 // indirect
 	github.com/morikuni/aec v1.0.0 // indirect
 	github.com/munnerz/goautoneg v0.0.0-20191010083416-a7dc8b61c822 // indirect
+	github.com/nats-io/nkeys v0.4.9 // indirect
+	github.com/nats-io/nuid v1.0.1 // indirect
 	github.com/opencontainers/go-digest v1.0.0 // indirect
 	github.com/opencontainers/image-spec v1.1.0 // indirect
 	github.com/pelletier/go-toml/v2 v2.2.2 // indirect

M go.sum

@@ -235,6 +235,12 @@ github.com/morikuni/aec v1.0.0 h1:nP9CBfwrvYnBRgY6qfDQkygYDmYwOilePFkwzv4dU8A=
 github.com/morikuni/aec v1.0.0/go.mod h1:BbKIizmSmc5MMPqRYbxO4ZU0S0+P200+tUnFx7PXmsc=
 github.com/munnerz/goautoneg v0.0.0-20191010083416-a7dc8b61c822 h1:C3w9PqII01/Oq1c1nUAm88MOHcQC9l5mIlSMApZMrHA=
 github.com/munnerz/goautoneg v0.0.0-20191010083416-a7dc8b61c822/go.mod h1:+n7T8mK8HuQTcFwEeznm/DIxMOiR9yIdICNftLE1DvQ=
+github.com/nats-io/nats.go v1.38.0 h1:A7P+g7Wjp4/NWqDOOP/K6hfhr54DvdDQUznt5JFg9XA=
+github.com/nats-io/nats.go v1.38.0/go.mod h1:IGUM++TwokGnXPs82/wCuiHS02/aKrdYUQkU8If6yjw=
+github.com/nats-io/nkeys v0.4.9 h1:qe9Faq2Gxwi6RZnZMXfmGMZkg3afLLOtrU+gDZJ35b0=
+github.com/nats-io/nkeys v0.4.9/go.mod h1:jcMqs+FLG+W5YO36OX6wFIFcmpdAns+w1Wm6D3I/evE=
+github.com/nats-io/nuid v1.0.1 h1:5iA8DT8V7q8WK2EScv2padNa/rTESc1KdnPw4TC2paw=
+github.com/nats-io/nuid v1.0.1/go.mod h1:19wcPz3Ph3q0Jbyiqsd0kePYG7A95tJPxeL+1OSON2c=
 github.com/opencontainers/go-digest v1.0.0 h1:apOUWs51W5PlhuyGyz9FCeeBIOUDA/6nW8Oi/yOhh5U=
 github.com/opencontainers/go-digest v1.0.0/go.mod h1:0JzlMkj0TRzQZfJkVvzbP0HBR3IKzErnv2BNG4W4MAM=
 github.com/opencontainers/image-spec v1.1.0 h1:8SG7/vwALn54lVB/0yZ/MMwhFrPYtpEHQb2IpWsCzug=

M infra/prometheus/prometheus.yml

@@ -10,4 +10,16 @@ scheme: http
     follow_redirects: true
     honor_timestamps: true
     static_configs:
-    - targets: [core:8001]
+      - targets: [core:8001]
+        labels:
+          service: "core"
+
+  - job_name: mailer
+    metrics_path: /metrics
+    scheme: http
+    follow_redirects: true
+    honor_labels: true
+    static_configs:
+      - targets: [mailer:8001]
+        labels:
+          service: "mailer"

M internal/config/config.go

@@ -11,6 +11,7 @@ type Config struct {
 	AppEnv     string
 	AppURL     string
 	ServerPort string
+	NatsURL    string
 
 	PostgresDSN      string
 	PasswordSalt     string
@@ -48,6 +49,7 @@ return &Config{
 		AppEnv:     getenvOrDefault("APP_ENV", "debug"),
 		AppURL:     getenvOrDefault("APP_URL", ""),
 		ServerPort: getenvOrDefault("SERVER_PORT", "3000"),
+		NatsURL:    getenvOrDefault("NATS_URL", ""),
 
 		PostgresDSN:      getenvOrDefault("POSTGRESQL_DSN", ""),
 		PasswordSalt:     getenvOrDefault("PASSWORD_SALT", ""),

A internal/events/events.go

@@ -0,0 +1,36 @@
+package events
+
+import (
+	"fmt"
+
+	"github.com/nats-io/nats.go"
+)
+
+const (
+	natsHeaderErrorCode = "Nats-Service-Error-Code"
+	natsHeaderErrorMsg  = "Nats-Service-Error"
+)
+
+var _ error = (*Error)(nil)
+
+type Error struct {
+	Code    string
+	Message string
+}
+
+func (e Error) Error() string {
+	return fmt.Sprintf("code: %s; msg: %s", e.Code, e.Message)
+}
+
+func CheckRespForError(resp *nats.Msg) error {
+	code := resp.Header.Get(natsHeaderErrorCode)
+	msg := resp.Header.Get(natsHeaderErrorMsg)
+	if code == "" && msg == "" {
+		return nil
+	}
+
+	return &Error{
+		Code:    code,
+		Message: msg,
+	}
+}

A internal/events/mailermq/mailermq.go

@@ -0,0 +1,62 @@
+package mailermq
+
+import (
+	"context"
+	"encoding/json"
+
+	"github.com/nats-io/nats.go"
+	"github.com/olexsmir/onasty/internal/events"
+	"github.com/olexsmir/onasty/internal/transport/http/reqid"
+)
+
+type Mailer interface {
+	SendVerificationEmail(ctx context.Context, input SendVerificationEmailRequest) error
+}
+
+type MailerMQ struct {
+	nc *nats.Conn
+}
+
+const sendMailSubject = "mailer.send"
+
+func New(nc *nats.Conn) *MailerMQ {
+	return &MailerMQ{
+		nc: nc,
+	}
+}
+
+type sendRequest struct {
+	RequestID    string            `json:"request_id"`
+	Receiver     string            `json:"receiver"`
+	TemplateName string            `json:"template_name"`
+	Options      map[string]string `json:"options"`
+}
+
+type SendVerificationEmailRequest struct {
+	Receiver string
+	Token    string
+}
+
+func (m MailerMQ) SendVerificationEmail(
+	ctx context.Context,
+	inp SendVerificationEmailRequest,
+) error {
+	req, err := json.Marshal(sendRequest{
+		RequestID:    reqid.GetContext(ctx),
+		Receiver:     inp.Receiver,
+		TemplateName: "email_verification",
+		Options: map[string]string{
+			"token": inp.Token,
+		},
+	})
+	if err != nil {
+		return err
+	}
+
+	resp, err := m.nc.RequestWithContext(ctx, sendMailSubject, req)
+	if err != nil {
+		return err
+	}
+
+	return events.CheckRespForError(resp)
+}

D

@@ -1,7 +0,0 @@
-package mailer
-
-import "context"
-
-type Mailer interface {
-	Send(ctx context.Context, to, subject, content string) error
-}

M mailer/mailgun.go →mailer/mailgun.go

@@ -1,13 +1,16 @@
-package mailer
+package main
 
 import (
 	"context"
 	"log/slog"
 
 	"github.com/mailgun/mailgun-go/v4"
-	"github.com/olexsmir/onasty/internal/metrics"
 	"github.com/olexsmir/onasty/internal/transport/http/reqid"
 )
+
+type Mailer interface {
+	Send(ctx context.Context, to, subject, content string) error
+}
 
 var _ Mailer = (*Mailgun)(nil)
 
@@ -33,13 +36,14 @@ slog.InfoContext(ctx, "email sent", "to", to)
 
 	_, _, err := m.mg.Send(ctx, msg)
 	if err != nil {
-		metrics.RecordEmailFailed(reqid.GetContext(ctx))
+		RecordEmailFailed(reqid.GetContext(ctx))
 		return err
 	}
 
 	slog.DebugContext(ctx, "email sent", "subject", subject, "content", content, "err", err)
 	slog.InfoContext(ctx, "email sent", "to", to)
-	metrics.RecordEmailSent()
+
+	RecordEmailSent()
 
 	return nil
 }

D

@@ -1,42 +0,0 @@
-package mailer
-
-import (
-	"context"
-	"sync"
-)
-
-var _ Mailer = (*TestMailer)(nil)
-
-type TestMailer struct {
-	mu sync.Mutex
-
-	emails map[string]string
-}
-
-// NewTestMailer create a mailer for tests
-// that implementation of Mailer stores all sent email in memory
-// to get the last email sent to a specific email use GetLastSentEmailToEmail
-func NewTestMailer() *TestMailer {
-	return &TestMailer{ //nolint:exhaustruct
-		emails: make(map[string]string),
-	}
-}
-
-func (t *TestMailer) Send(_ context.Context, to, _, content string) error {
-	t.mu.Lock()
-	defer t.mu.Unlock()
-
-	t.emails[to] = content
-
-	return nil
-}
-
-// GetLastSentEmailToEmail returns the last email sent to a specific email
-func (t *TestMailer) GetLastSentEmailToEmail(email string) string {
-	t.mu.Lock()
-	defer t.mu.Unlock()
-
-	e := t.emails[email]
-
-	return e
-}

D

@@ -1,33 +0,0 @@
-package mailer
-
-import (
-	"context"
-	"testing"
-
-	"github.com/stretchr/testify/assert"
-	"github.com/stretchr/testify/require"
-)
-
-func TestMailer_Send(t *testing.T) {
-	m := NewTestMailer()
-	assert.Empty(t, m.emails)
-
-	email := "test@mail.com"
-	err := m.Send(context.TODO(), email, "", "content")
-	require.NoError(t, err)
-
-	assert.Equal(t, "content", m.emails[email])
-}
-
-func TestMailer_GetLastSentEmailToEmail(t *testing.T) {
-	email := "test@mail.com"
-	content := "content"
-
-	m := NewTestMailer()
-	assert.Empty(t, m.emails)
-
-	m.emails[email] = content
-
-	c := m.GetLastSentEmailToEmail(email)
-	assert.Equal(t, content, c)
-}

D

@@ -1,42 +0,0 @@
-package usersrv
-
-import (
-	"context"
-	"errors"
-	"fmt"
-	"log/slog"
-)
-
-var ErrFailedToSendVerifcationEmail = errors.New("failed to send verification email")
-
-const (
-	verificationEmailSubject = "Onasty: verify your email"
-	verificationEmailBody    = `To verify your email, please follow this link:
-<a href="%[1]s/api/v1/auth/verify/%[2]s">%[1]s/api/v1/auth/verify/%[2]s</a>
-<br />
-<br />
-This link will expire after 24 hours.`
-)
-
-func (u *UserSrv) sendVerificationEmail(
-	ctx context.Context,
-	cancel context.CancelFunc,
-	userEmail string,
-	token string,
-	url string,
-) {
-	select {
-	case <-ctx.Done():
-		slog.ErrorContext(ctx, "failed to send verification email", "err", ctx.Err())
-	default:
-		if err := u.mailer.Send(
-			ctx,
-			userEmail,
-			verificationEmailSubject,
-			fmt.Sprintf(verificationEmailBody, url, token),
-		); err != nil {
-			slog.ErrorContext(ctx, "failed to send verification email", "err", err)
-		}
-		cancel()
-	}
-}

M internal/service/usersrv/usersrv.go

@@ -8,15 +8,14 @@ "time"
 
 	"github.com/gofrs/uuid/v5"
 	"github.com/olexsmir/onasty/internal/dtos"
+	"github.com/olexsmir/onasty/internal/events/mailermq"
 	"github.com/olexsmir/onasty/internal/hasher"
 	"github.com/olexsmir/onasty/internal/jwtutil"
-	"github.com/olexsmir/onasty/internal/mailer"
 	"github.com/olexsmir/onasty/internal/models"
 	"github.com/olexsmir/onasty/internal/store/psql/sessionrepo"
 	"github.com/olexsmir/onasty/internal/store/psql/userepo"
 	"github.com/olexsmir/onasty/internal/store/psql/vertokrepo"
 	"github.com/olexsmir/onasty/internal/store/rdb/usercache"
-	"github.com/olexsmir/onasty/internal/transport/http/reqid"
 )
 
 type UserServicer interface {
@@ -44,7 +43,7 @@ sessionstore sessionrepo.SessionStorer
 	vertokrepo   vertokrepo.VerificationTokenStorer
 	hasher       hasher.Hasher
 	jwtTokenizer jwtutil.JWTTokenizer
-	mailer       mailer.Mailer
+	mailermq     mailermq.Mailer
 	cache        usercache.UserCacheer
 
 	refreshTokenTTL      time.Duration
@@ -58,7 +57,7 @@ sessionstore sessionrepo.SessionStorer,
 	vertokrepo vertokrepo.VerificationTokenStorer,
 	hasher hasher.Hasher,
 	jwtTokenizer jwtutil.JWTTokenizer,
-	mailer mailer.Mailer,
+	mailermq mailermq.Mailer,
 	cache usercache.UserCacheer,
 	refreshTokenTTL, verificationTokenTTL time.Duration,
 	appURL string,
@@ -69,7 +68,7 @@ sessionstore:         sessionstore,
 		vertokrepo:           vertokrepo,
 		hasher:               hasher,
 		jwtTokenizer:         jwtTokenizer,
-		mailer:               mailer,
+		mailermq:             mailermq,
 		cache:                cache,
 		refreshTokenTTL:      refreshTokenTTL,
 		verificationTokenTTL: verificationTokenTTL,
@@ -99,8 +98,12 @@ if err := u.vertokrepo.Create(ctx, vtok, uid, time.Now(), time.Now().Add(u.verificationTokenTTL)); err != nil {
 		return uuid.Nil, err
 	}
 
-	sendingCtx, cancel := getContextForEmailSending(ctx)
-	go u.sendVerificationEmail(sendingCtx, cancel, inp.Email, vtok, u.appURL)
+	if err := u.mailermq.SendVerificationEmail(ctx, mailermq.SendVerificationEmailRequest{
+		Receiver: inp.Email,
+		Token:    vtok,
+	}); err != nil {
+		return uuid.Nil, err
+	}
 
 	return uid, nil
 }
@@ -221,8 +224,12 @@ if err != nil {
 		return err
 	}
 
-	sendingCtx, cancel := getContextForEmailSending(ctx)
-	go u.sendVerificationEmail(sendingCtx, cancel, inp.Email, token, u.appURL)
+	if err := u.mailermq.SendVerificationEmail(ctx, mailermq.SendVerificationEmailRequest{
+		Receiver: inp.Email,
+		Token:    token,
+	}); err != nil {
+		return err
+	}
 
 	return nil
 }
@@ -285,11 +292,3 @@ Access:  accessToken,
 		Refresh: refreshToken,
 	}, err
 }
-
-func getContextForEmailSending(ctx context.Context) (context.Context, context.CancelFunc) {
-	rid := reqid.GetContext(ctx)
-	resCtx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
-	resCtx = reqid.SetContext(resCtx, rid)
-
-	return resCtx, cancel
-}

A mailer/.env.example

@@ -0,0 +1,10 @@
+APP_URL=http://localhost:8000
+NATS_URL="nats:4222"
+METRICS_ENABLED=true
+METRICS_PORT=8001
+LOG_LEVEL=debug
+LOG_FORMAT=text
+LOG_SHOW_LINE=true
+MAILGUN_FROM=onasty@mail.com
+MAILGUN_DOMAI='<domain>'
+MAILGUN_API_KEY='<token>'

A mailer/Dockerfile

@@ -0,0 +1,18 @@
+FROM golang:1.23.3-alpine AS builder
+
+WORKDIR /app
+
+COPY go.mod go.sum ./
+RUN go mod download
+
+COPY internal internal
+COPY mailer mailer
+
+ENV CGO_ENABLED=0 GOOS=linux GOARCH=amd64
+RUN go build -trimpath -ldflags='-w -s' -o /mailer ./mailer
+
+
+FROM alpine:3.20
+COPY --from=builder /mailer /mailer
+RUN apk --no-cache add ca-certificates
+ENTRYPOINT ["/mailer"]

A mailer/README.md

@@ -0,0 +1,41 @@
+# mailer service
+
+All templates could be found *[here](./template.go)*
+
+## endpoints
+### `mailer.ping`
+This endpoint always returns pong message
+
+Response:
+```json
+{
+  "message": "pong"
+}
+```
+
+### `mailer.send`
+
+Input
+- `request_id` : *string* - (optional) the request id, needed to keep consistency across services
+- `receiver` : *string* - the email receiver
+- `template_name` : *string* - the template that's going to be used
+- `options` : *Map<string, string>* - template specific options
+
+
+Example input
+```json
+{
+  "request_id": "hello_world",
+  "receiver": "onasty@example.com",
+  "template_name": "email_verification",
+  "options": {
+    "token": "the_verification_token"
+  }
+}
+```
+
+#### Template specific options
+- `email_verification`
+  - `token` the token that is used in verification link
+
+

A mailer/config.go

@@ -0,0 +1,40 @@
+package main
+
+import "os"
+
+type Config struct {
+	AppURL        string
+	NatsURL       string
+	MailgunFrom   string
+	MailgunDomain string
+	MailgunAPIKey string
+
+	LogLevel    string
+	LogFormat   string
+	LogShowLine bool
+
+	MetricsEnabled bool
+	MetricsPort    string
+}
+
+func NewConfig() *Config {
+	return &Config{
+		AppURL:         getenvOrDefault("APP_URL", ""),
+		NatsURL:        getenvOrDefault("NATS_URL", ""),
+		MailgunFrom:    getenvOrDefault("MAILGUN_FROM", ""),
+		MailgunDomain:  getenvOrDefault("MAILGUN_DOMAIN", ""),
+		MailgunAPIKey:  getenvOrDefault("MAILGUN_API_KEY", ""),
+		LogLevel:       getenvOrDefault("LOG_LEVEL", "debug"),
+		LogFormat:      getenvOrDefault("LOG_FORMAT", "json"),
+		LogShowLine:    getenvOrDefault("LOG_SHOW_LINE", "true") == "true",
+		MetricsPort:    getenvOrDefault("METRICS_PORT", ""),
+		MetricsEnabled: getenvOrDefault("METRICS_ENABLED", "true") == "true",
+	}
+}
+
+func getenvOrDefault(key, def string) string {
+	if v, ok := os.LookupEnv(key); ok {
+		return v
+	}
+	return def
+}

A mailer/handlers.go

@@ -0,0 +1,69 @@
+package main
+
+import (
+	"context"
+	"encoding/json"
+	"log/slog"
+	"time"
+
+	"github.com/nats-io/nats.go/micro"
+	"github.com/olexsmir/onasty/internal/transport/http/reqid"
+)
+
+type Handlers struct {
+	service *Service
+}
+
+func NewHandlers(service *Service) *Handlers {
+	return &Handlers{
+		service: service,
+	}
+}
+
+func (h Handlers) RegisterAll(svc micro.Service) error {
+	m := svc.AddGroup("mailer")
+	if err := m.AddEndpoint("ping", micro.HandlerFunc(h.pingHandler)); err != nil {
+		return err
+	}
+
+	if err := m.AddEndpoint("send", micro.HandlerFunc(h.sendHandler)); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+type pingResponse struct {
+	Message string `json:"message"`
+}
+
+func (h Handlers) pingHandler(req micro.Request) {
+	_ = req.RespondJSON(pingResponse{
+		Message: "pong",
+	})
+}
+
+type sendRequest struct {
+	RequestID string `json:"request_id"`
+
+	Receiver     string            `json:"receiver"`
+	TemplateName string            `json:"template_name"`
+	Options      map[string]string `json:"options"`
+}
+
+func (h Handlers) sendHandler(req micro.Request) {
+	var inp sendRequest
+	if err := json.Unmarshal(req.Data(), &inp); err != nil {
+		slog.Error("failed to unmarshal input data", "err", err)
+		return
+	}
+
+	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
+	ctx = reqid.SetContext(ctx, inp.RequestID)
+
+	if err := h.service.Send(ctx, cancel, inp.Receiver, inp.TemplateName, inp.Options); err != nil {
+		_ = req.Error("500", err.Error(), nil)
+	}
+
+	_ = req.Respond(nil)
+}

A mailer/main.go

@@ -0,0 +1,92 @@
+package main
+
+import (
+	"errors"
+	"fmt"
+	"log/slog"
+	"net/http"
+	"os"
+	"os/signal"
+	"strings"
+	"syscall"
+
+	"github.com/nats-io/nats.go"
+	"github.com/nats-io/nats.go/micro"
+	"github.com/olexsmir/onasty/internal/logger"
+	"github.com/olexsmir/onasty/internal/transport/http/httpserver"
+
+	_ "embed"
+)
+
+//go:embed version
+var _version string
+
+var version = strings.Trim(_version, "\n")
+
+func main() {
+	if err := run(); err != nil {
+		fmt.Fprintf(os.Stderr, "error: %v\n", err)
+		os.Exit(1)
+	}
+}
+
+func run() error {
+	cfg := NewConfig()
+	nc, err := nats.Connect(cfg.NatsURL)
+	if err != nil {
+		return err
+	}
+
+	logger, err := logger.NewCustomLogger(cfg.LogLevel, cfg.LogFormat, cfg.LogShowLine)
+	if err != nil {
+		return err
+	}
+
+	slog.SetDefault(logger)
+
+	//nolint:exhaustruct
+	svc, err := micro.AddService(nc, micro.Config{
+		Name:    "mailer",
+		Version: version,
+	})
+	if err != nil {
+		return err
+	}
+
+	mg := NewMailgun(cfg.MailgunFrom, cfg.MailgunDomain, cfg.MailgunAPIKey)
+	service := NewService(cfg.AppURL, mg)
+	handlers := NewHandlers(service)
+
+	if err := handlers.RegisterAll(svc); err != nil {
+		return err
+	}
+
+	if cfg.MetricsEnabled {
+		srv := httpserver.NewServer(cfg.MetricsPort, MetricsHandler())
+		go func() {
+			slog.Info("starting metrics server", "port", cfg.MetricsPort)
+			if err := srv.Start(); !errors.Is(err, http.ErrServerClosed) {
+				slog.Error("failed to start metrics server", "error", err)
+			}
+		}()
+	}
+
+	slog.Info("the service is listening")
+
+	// graceful shutdown
+	quitCh := make(chan os.Signal, 1)
+	signal.Notify(quitCh, syscall.SIGINT, syscall.SIGTERM)
+	<-quitCh
+
+	slog.Info("stopping the service")
+
+	if err := svc.Stop(); err != nil {
+		return err
+	}
+
+	if err := nc.Drain(); err != nil {
+		return err
+	}
+
+	return nil
+}

A mailer/metrics.go

@@ -0,0 +1,37 @@
+package main
+
+import (
+	"net/http"
+
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promauto"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
+)
+
+var (
+	emailSentSuccessfully = promauto.NewCounter(prometheus.CounterOpts{ //nolint:exhaustruct
+		Name: "mail_sent_total",
+		Help: "the total number of successfully sent email",
+	})
+
+	emailFailedToSend = promauto.NewCounterVec(prometheus.CounterOpts{ //nolint:exhaustruct
+		Name: "mail_failed_total",
+		Help: "the total number of email that failed to send",
+	}, []string{"request_id"})
+)
+
+func MetricsHandler() http.Handler {
+	mux := http.NewServeMux()
+	mux.Handle("GET /metrics", promhttp.Handler())
+	return mux
+}
+
+func RecordEmailSent() {
+	go emailSentSuccessfully.Inc()
+}
+
+func RecordEmailFailed(reqid string) {
+	go emailFailedToSend.With(prometheus.Labels{
+		"request_id": reqid,
+	}).Inc()
+}

A mailer/service.go

@@ -0,0 +1,47 @@
+package main
+
+import (
+	"context"
+	"log/slog"
+)
+
+type Service struct {
+	appURL string
+	mg     *Mailgun
+}
+
+func NewService(appURL string, mg *Mailgun) *Service {
+	return &Service{
+		appURL: appURL,
+		mg:     mg,
+	}
+}
+
+func (s Service) Send(
+	ctx context.Context,
+	cancel context.CancelFunc,
+	receiver, templateName string,
+	templateOpts map[string]string,
+) error {
+	tmpl, err := getTemplate(s.appURL, templateName)
+	if err != nil {
+		return err
+	}
+
+	t := tmpl(templateOpts)
+
+	go func() {
+		select {
+		case <-ctx.Done():
+			slog.ErrorContext(ctx, "failed to send verification email", "err", ctx.Err())
+			return
+		default:
+			if err := s.mg.Send(ctx, receiver, t.Subject, t.Body); err != nil {
+				slog.ErrorContext(ctx, "failed to send verification email", "err", err)
+			}
+			cancel()
+		}
+	}()
+
+	return nil
+}

A mailer/template.go

@@ -0,0 +1,34 @@
+package main
+
+import (
+	"errors"
+	"fmt"
+)
+
+type Template struct {
+	Subject string
+	Body    string
+}
+
+type TemplateFunc func(args map[string]string) Template
+
+func getTemplate(appURL string, templateName string) (TemplateFunc, error) {
+	if templateName == "email_verification" {
+		return emailVerificationTemplate(appURL), nil
+	}
+
+	return nil, errors.New("failed to get template") //nolint:err113
+}
+
+func emailVerificationTemplate(appURL string) TemplateFunc {
+	return func(opts map[string]string) Template {
+		return Template{
+			Subject: "Onasty: verify your email",
+			Body: fmt.Sprintf(`To verify your email, please follow this link:
+<a href="%[1]s/api/v1/auth/verify/%[2]s">%[1]s/api/v1/auth/verify/%[2]s</a>
+<br />
+<br />
+This link will expire after 24 hours.`, appURL, opts["token"]),
+		}
+	}
+}

A mailer/version

@@ -0,0 +1,1 @@
+0.1.0