AWS ALB/ELB Load Balancing Setup for High-Load Websites

AWS ALB/ELB Load Balancing Setup

Website crashing under load? 502 errors during peak promotional traffic? We've encountered this in projects with 100k+ RPS. Load balancing with AWS ALB is the standard solution for high-load projects. We configure ALB/ELB turnkey: target groups, listener rules, SSL, Auto Scaling integration. 7+ years of experience, 50+ configured load balancers. Proper ALB configuration is critical for site availability and speed — significant infrastructure savings with competent tuning.

AWS provides managed load balancers without needing to maintain your own server. Application Load Balancer (ALB) works at HTTP/HTTPS level with routing by path and headers. Network Load Balancer (NLB) — L4 TCP/UDP with minimal latency. Classic ELB is deprecated and not recommended for new projects.

Why Choose ALB over NLB?

ALB is better than NLB for HTTP/HTTPS: it supports intelligent routing, WAF integration, and static content delivery. NLB is indispensable for TCP services requiring static IPs and minimal latency. If you have a React/Vue web application or Node.js API — choose ALB. For GameServer or VoIP — NLB. We often combine them: ALB for web, NLB for WebSocket.

How ALB Works with Auto Scaling?

Attach an ALB target group to an Auto Scaling Group. When scaling, new instances automatically register and start receiving traffic. ALB health check (path /health, threshold of 2 successful responses) determines when the instance is ready to accept requests. This ensures zero-downtime deployment. For critical services we use target groups with deregistration_delay of 30 seconds to allow in-flight requests to complete.

Step-by-Step ALB Setup via Terraform

1. Create an ALB with security groups and subnets.
2. Configure HTTPS listener with ACM certificate and HTTP redirect.
3. Define target groups with health check and stickiness.
4. Add listener rules for routing by paths, headers, or hosts.
5. Attach target group to your service (EC2, ECS, Lambda).
6. Enable access logs and monitoring.

Full configuration example below.

Application Load Balancer

ALB is the standard choice for web applications. Routes by path, host, HTTP headers, method, query string. Integrates with ECS, EKS, Lambda, Auto Scaling Groups. Below is a complete configuration with AWS ALB, routing, and ACM.

# Terraform: полная конфигурация ALB + routing + ACM resource "aws_lb" "main" { name = "myapp-alb" internal = false load_balancer_type = "application" security_groups = [aws_security_group.alb.id] subnets = aws_subnet.public[*].id enable_deletion_protection = true enable_cross_zone_load_balancing = true drop_invalid_header_fields = true access_logs { bucket = aws_s3_bucket.alb_logs.bucket prefix = "alb" enabled = true } tags = { Name = "myapp-alb" } } # HTTPS Listener resource "aws_lb_listener" "https" { load_balancer_arn = aws_lb.main.arn port = 443 protocol = "HTTPS" ssl_policy = "ELBSecurityPolicy-TLS13-1-2-2021-06" certificate_arn = aws_acm_certificate.main.arn default_action { type = "forward" target_group_arn = aws_lb_target_group.web.arn } } # HTTP → HTTPS redirect resource "aws_lb_listener" "http" { load_balancer_arn = aws_lb.main.arn port = 80 protocol = "HTTP" default_action { type = "redirect" redirect { port = "443" protocol = "HTTPS" status_code = "HTTP_301" } } } # Target Group для веб-приложения resource "aws_lb_target_group" "web" { name = "myapp-web-tg" port = 8080 protocol = "HTTP" vpc_id = aws_vpc.main.id target_type = "ip" # для ECS Fargate health_check { enabled = true path = "/health" healthy_threshold = 2 unhealthy_threshold = 3 timeout = 5 interval = 10 matcher = "200" } deregistration_delay = 30 stickiness { type = "lb_cookie" cookie_duration = 86400 enabled = false } } # API Target Group resource "aws_lb_target_group" "api" { name = "myapp-api-tg" port = 3000 protocol = "HTTP" vpc_id = aws_vpc.main.id health_check { path = "/api/health" matcher = "200" } } # Правила маршрутизации resource "aws_lb_listener_rule" "api" { listener_arn = aws_lb_listener.https.arn priority = 10 action { type = "forward" target_group_arn = aws_lb_target_group.api.arn } condition { path_pattern { values = ["/api/*"] } } } # Маршрут по заголовку (версионирование API) resource "aws_lb_listener_rule" "api_v2" { listener_arn = aws_lb_listener.https.arn priority = 5 action { type = "forward" target_group_arn = aws_lb_target_group.api_v2.arn } condition { http_header { http_header_name = "X-API-Version" values = ["2", "2.0"] } } } # Weighted forwarding для Canary deployments resource "aws_lb_listener_rule" "canary" { listener_arn = aws_lb_listener.https.arn priority = 20 action { type = "forward" forward { target_group { arn = aws_lb_target_group.web_stable.arn weight = 95 } target_group { arn = aws_lb_target_group.web_canary.arn weight = 5 } stickiness { enabled = true duration = 3600 } } } condition { path_pattern { values = ["/*"] } } } # Сертификат ACM resource "aws_acm_certificate" "main" { domain_name = "example.com" subject_alternative_names = ["*.example.com"] validation_method = "DNS" lifecycle { create_before_destroy = true } } resource "aws_route53_record" "cert_validation" { for_each = { for dvo in aws_acm_certificate.main.domain_validation_options : dvo.domain_name => { name = dvo.resource_record_name record = dvo.resource_record_value type = dvo.resource_record_type } } zone_id = aws_route53_zone.main.zone_id name = each.value.name type = each.value.type ttl = 60 records = [each.value.record] } resource "aws_acm_certificate_validation" "main" { certificate_arn = aws_acm_certificate.main.arn validation_record_fqdns = [for record in aws_route53_record.cert_validation : record.fqdn] } 

ALB + WAF

We integrate WAF for protection against OWASP top-10 and rate limiting.

resource "aws_wafv2_web_acl_association" "alb" { resource_arn = aws_lb.main.arn web_acl_arn = aws_wafv2_web_acl.main.arn } resource "aws_wafv2_web_acl" "main" { name = "myapp-waf" scope = "REGIONAL" default_action { allow {} } rule { name = "AWSManagedRulesCommonRuleSet" priority = 1 override_action { none {} } statement { managed_rule_group_statement { name = "AWSManagedRulesCommonRuleSet" vendor_name = "AWS" } } visibility_config { cloudwatch_metrics_enabled = true metric_name = "CommonRuleSet" sampled_requests_enabled = true } } rule { name = "RateLimit" priority = 2 action { block {} } statement { rate_based_statement { limit = 2000 aggregate_key_type = "IP" } } visibility_config { cloudwatch_metrics_enabled = true metric_name = "RateLimit" sampled_requests_enabled = true } } visibility_config { cloudwatch_metrics_enabled = true metric_name = "MyAppWAF" sampled_requests_enabled = true } } 

ALB + ECS Fargate

Example of ALB integration with Fargate: the service automatically registers in the target group.

resource "aws_ecs_service" "app" { name = "myapp-web" cluster = aws_ecs_cluster.main.id task_definition = aws_ecs_task_definition.app.arn desired_count = 3 launch_type = "FARGATE" network_configuration { subnets = aws_subnet.private[*].id security_groups = [aws_security_group.app.id] assign_public_ip = false } load_balancer { target_group_arn = aws_lb_target_group.web.arn container_name = "web" container_port = 8080 } deployment_circuit_breaker { enable = true rollback = true } deployment_controller { type = "ECS" } depends_on = [aws_lb_listener.https] } 

Network Load Balancer

NLB for TCP/UDP with static IPs and minimal latency.

resource "aws_lb" "nlb" { name = "myapp-nlb" internal = false load_balancer_type = "network" subnets = aws_subnet.public[*].id enable_cross_zone_load_balancing = true } resource "aws_lb_listener" "nlb_tls" { load_balancer_arn = aws_lb.nlb.arn port = 443 protocol = "TLS" ssl_policy = "ELBSecurityPolicy-TLS13-1-2-2021-06" certificate_arn = aws_acm_certificate.main.arn default_action { type = "forward" target_group_arn = aws_lb_target_group.nlb_tcp.arn } } resource "aws_lb_target_group" "nlb_tcp" { name = "myapp-nlb-tg" port = 8080 protocol = "TCP" vpc_id = aws_vpc.main.id health_check { protocol = "HTTP" path = "/health" healthy_threshold = 2 unhealthy_threshold = 2 interval = 10 } } 

Monitoring ALB

Key CloudWatch metrics: RequestCount, ActiveConnectionCount, TargetResponseTime (p50/p95/p99), HTTPCode_ELB_5XX_Count, HealthyHostCount, UnHealthyHostCount. We set up alerts for 5xx and high latency.

resource "aws_cloudwatch_metric_alarm" "target_5xx" { alarm_name = "alb-5xx-errors" comparison_operator = "GreaterThanThreshold" evaluation_periods = 2 metric_name = "HTTPCode_Target_5XX_Count" namespace = "AWS/ApplicationELB" period = 60 statistic = "Sum" threshold = 10 alarm_actions = [aws_sns_topic.alerts.arn] dimensions = { LoadBalancer = aws_lb.main.arn_suffix } } resource "aws_cloudwatch_metric_alarm" "latency" { alarm_name = "alb-high-latency" comparison_operator = "GreaterThanThreshold" evaluation_periods = 3 metric_name = "TargetResponseTime" namespace = "AWS/ApplicationELB" period = 60 extended_statistic = "p95" threshold = 2.0 alarm_actions = [aws_sns_topic.alerts.arn] dimensions = { LoadBalancer = aws_lb.main.arn_suffix } } 

What's Included in the Work

• Load balancing design: type selection (ALB/NLB), network scheme.
• Terraform code with target groups, listener rules, ACM, WAF.
• Monitoring and alert setup.
• Integration with CI/CD and Auto Scaling.
• Operations documentation and team training.

Implementation Timelines

Typical Configuration Mistakes

• Health check not configured — instances receive traffic before readiness.
• Deletion protection missing — accidental ALB deletion.
• Incorrect SSL policy — vulnerabilities.
• Click-through on WAF — managed rules not enabled.

We guarantee stability and performance. Get a consultation on ALB setup for your project. Contact us — we'll estimate timelines for your case. AWS ALB Documentation can help delve deeper into capabilities.