Implement production-grade email retry optimization

docker-compose.yml

@@ -29,7 +29,7 @@ services:
     ports:
       - "8080:8080"
     env_file:
-      - .env.prod
+      - .env.dev
     environment:
       SPRING_PROFILES_ACTIVE: prod
     restart: unless-stopped

src/main/java/com/vimaltech/contactapi/config/SchedulerConfig.java

@@ -0,0 +1,9 @@
+package com.vimaltech.contactapi.config;
+
+import org.springframework.context.annotation.Configuration;
+import org.springframework.scheduling.annotation.EnableScheduling;
+
+@Configuration
+@EnableScheduling
+public class SchedulerConfig {
+}

src/main/java/com/vimaltech/contactapi/entity/EmailLog.java

@@ -0,0 +1,51 @@
+package com.vimaltech.contactapi.entity;
+
+import com.vimaltech.contactapi.enums.EmailStatus;
+import jakarta.persistence.*;
+import lombok.*;
+
+import java.time.LocalDateTime;
+
+@Entity
+@Table(name = "email_logs")
+@Getter
+@Setter
+@NoArgsConstructor
+@AllArgsConstructor
+@Builder
+public class EmailLog {
+
+    @Id
+    @GeneratedValue(strategy = GenerationType.IDENTITY)
+    private Long id;
+
+    @Column(nullable = false)
+    private String toEmail;
+
+    @Column(nullable = false)
+    private String subject;
+
+    @Column(nullable = false, columnDefinition = "TEXT")
+    private String body;
+
+    @Enumerated(EnumType.STRING)
+    @Column(nullable = false)
+    private EmailStatus status;
+
+    @Column(nullable = false)
+    private int retryCount;
+
+    @Column(length = 1000)
+    private String lastError;
+
+    @Column(name = "created_at", nullable = false, updatable = false)
+    private LocalDateTime createdAt;
+
+    @Column(name = "last_attempt_at")
+    private LocalDateTime lastAttemptAt;
+
+    @PrePersist
+    public void prePersist() {
+        this.createdAt = LocalDateTime.now();
+    }
+}

src/main/java/com/vimaltech/contactapi/enums/EmailStatus.java

@@ -0,0 +1,10 @@
+package com.vimaltech.contactapi.enums;
+
+public enum EmailStatus {
+
+    PENDING,
+    SENT,
+    FAILED,
+    IN_PROGRESS,
+    FAILED_PERMANENT
+}

src/main/java/com/vimaltech/contactapi/repository/EmailLogRepository.java

@@ -0,0 +1,17 @@
+package com.vimaltech.contactapi.repository;
+
+import com.vimaltech.contactapi.entity.EmailLog;
+import com.vimaltech.contactapi.enums.EmailStatus;
+import org.springframework.data.jpa.repository.JpaRepository;
+import org.springframework.stereotype.Repository;
+
+import java.util.List;
+
+@Repository
+public interface EmailLogRepository
+        extends JpaRepository<EmailLog, Long> {
+
+    List<EmailLog> findTop10ByStatusOrderByCreatedAtAsc(
+            EmailStatus status
+    );
+}

src/main/java/com/vimaltech/contactapi/service/EmailRetryScheduler.java

@@ -0,0 +1,88 @@
+package com.vimaltech.contactapi.service;
+
+import com.vimaltech.contactapi.entity.EmailLog;
+import com.vimaltech.contactapi.enums.EmailStatus;
+import com.vimaltech.contactapi.repository.EmailLogRepository;
+import lombok.RequiredArgsConstructor;
+import lombok.extern.slf4j.Slf4j;
+import org.springframework.scheduling.annotation.Scheduled;
+import org.springframework.stereotype.Service;
+
+import java.time.LocalDateTime;
+import java.util.List;
+
+@Service
+@RequiredArgsConstructor
+@Slf4j
+public class EmailRetryScheduler {
+
+    private static final int MAX_RETRIES = 3;
+
+    private final EmailLogRepository emailLogRepository;
+    private final EmailService emailService;
+
+    @Scheduled(fixedDelay = 60000)
+    public void retryFailedEmails() {
+
+        List<EmailLog> failedEmails =
+                emailLogRepository
+                        .findTop10ByStatusOrderByCreatedAtAsc(
+                                EmailStatus.FAILED
+                        );
+
+        if (failedEmails.isEmpty()) {
+            return;
+        }
+
+        log.info(
+                "Retry scheduler found {} failed emails",
+                failedEmails.size()
+        );
+
+        for (EmailLog emailLog : failedEmails) {
+
+            /*
+             * Prevent infinite retry polling
+             */
+            if (emailLog.getRetryCount() >= MAX_RETRIES) {
+
+                emailLog.setStatus(
+                        EmailStatus.FAILED_PERMANENT
+                );
+
+                emailLog.setLastError(
+                        "Retry limit exhausted"
+                );
+
+                emailLogRepository.save(emailLog);
+
+                log.error(
+                        "Email permanently failed after {} retries. Email ID={}",
+                        emailLog.getRetryCount(),
+                        emailLog.getId()
+                );
+
+                continue;
+            }
+
+            /*
+             * Prevent retry spam within 1 minute
+             */
+            if (emailLog.getLastAttemptAt() != null
+                    && emailLog.getLastAttemptAt()
+                    .isAfter(LocalDateTime.now().minusMinutes(1))) {
+
+                continue;
+            }
+
+            log.warn(
+                    "Retrying email attempt {}/{} for email id={}",
+                    emailLog.getRetryCount() + 1,
+                    MAX_RETRIES,
+                    emailLog.getId()
+            );
+
+            emailService.retryEmail(emailLog);
+        }
+    }
+}

src/main/java/com/vimaltech/contactapi/service/EmailService.java

@@ -1,7 +1,10 @@
 package com.vimaltech.contactapi.service;
 
 import com.vimaltech.contactapi.dto.EmailRequest;
+import com.vimaltech.contactapi.entity.EmailLog;
 
 public interface EmailService {
     void sendEmail(EmailRequest request);
+
+    void retryEmail(EmailLog emailLog);
 }

src/main/java/com/vimaltech/contactapi/service/impl/DevEmailService.java

@@ -0,0 +1,59 @@
+package com.vimaltech.contactapi.service.impl;
+
+import com.vimaltech.contactapi.dto.EmailRequest;
+import com.vimaltech.contactapi.entity.EmailLog;
+import com.vimaltech.contactapi.service.EmailService;
+import lombok.extern.slf4j.Slf4j;
+import org.springframework.context.annotation.Profile;
+import org.springframework.stereotype.Service;
+
+@Service
+@Profile("dev")
+@Slf4j
+public class DevEmailService implements EmailService {
+
+    @Override
+    public void sendEmail(EmailRequest request) {
+
+        log.info("""
+
+                ==============================
+                DEV EMAIL SIMULATION
+                ==============================
+                TO: {}
+                SUBJECT: {}
+
+                BODY:
+                {}
+                ==============================
+                """,
+                request.getTo(),
+                request.getSubject(),
+                request.getBody()
+        );
+    }
+
+    @Override
+    public void retryEmail(EmailLog emailLog) {
+
+        log.info("""
+
+            ==============================
+            DEV EMAIL RETRY
+            ==============================
+            TO: {}
+            SUBJECT: {}
+
+            BODY:
+            {}
+
+            RETRY COUNT: {}
+            ==============================
+            """,
+                emailLog.getToEmail(),
+                emailLog.getSubject(),
+                emailLog.getBody(),
+                emailLog.getRetryCount()
+        );
+    }
+}

src/main/java/com/vimaltech/contactapi/service/impl/NoOpEmailService.java

@@ -1,6 +1,7 @@
 package com.vimaltech.contactapi.service.impl;
 
 import com.vimaltech.contactapi.dto.EmailRequest;
+import com.vimaltech.contactapi.entity.EmailLog;
 import com.vimaltech.contactapi.service.EmailService;
 import lombok.extern.slf4j.Slf4j;
 import org.springframework.context.annotation.Profile;
@@ -15,4 +16,9 @@ public class NoOpEmailService implements EmailService {
     public void sendEmail(EmailRequest request) {
         log.warn("Email disabled (NoOp) | to={}", request.getTo());
     }
+
+    @Override
+    public void retryEmail(EmailLog emailLog) {
+
+    }
 }