Application load balancing is critical for scaling web applications. An Application Load Balancer (ALB) routes traffic intelligently across multiple servers to optimize performance, availability, and fault tolerance.
This comprehensive guide will walk you through everything you need to know to fully utilize Elastic Load Balancing capabilities for your infrastructure. You‘ll learn:
- Capabilities and benefits of ALBs
- Comparison to Classic Load Balancers
- Key features and use cases
- Architecture best practices
- Optimization, security, and automation
- Migration considerations
- And much more
Let‘s get started.
Why You Need Application Load Balancing
An Application Load Balancer is a next-generation service designed specifically to improve scalability, availability, and manageability of HTTP/HTTPS applications:
High Performance
- Smart load balancing algorithms
- Dynamic scaling up to 125,000 requests per second
- Native acceleration technologies like HTTP/2 prioritization
High Availability
- Automated failover across multiple AZs
- Health checks identify unhealthy hosts
- Maintains SLA compliance even during outages
Advanced Traffic Management
- Route requests based on content and context
- Session affinity/stickiness for persistent connections
- Direct integration with critical AWS services
Operational Insights
- Access logs offer detailed request tracing
- CloudWatch metrics monitor performance
- Dashboard visualizations reveal traffic insights
Simplified Scaling
- Programmatic capacity provisioning via SDK/CLI
- Integration with Auto Scaling groups
- Expand to sudden traffic spikes easily
Enhanced Security
- Native integration with AWS Web Application Firewall
- Takes over transport layer encryption so apps don‘t have to
- Lock down access rules, data flows, and audit controls
Industry surveys show over 90% of companies leveraging Elastic Load Balancing for their production workloads. Analyst firm ESG concluded that businesses running apps on AWS accelerate time-to-market by up to 66% compared to on-premises.
Are you ready to unlock the possibilities? Let‘s examine ALB capabilities more closely.
Key Components and Architecture
Image source: Geekflare
ALBs manage traffic flowing between clients and registered backend targets. Key logical components include:
Listeners
Listeners check for connection requests from clients using protocol and port configurations. HTTP, HTTPS, TCP and UDP listeners are all supported.
Target Groups
Target groups route requests to registered target VMs, containers, IP addresses or Lambda functions. Health checks validate availability.
Targets
Targets handle incoming requests and provide back-end application services. Each target must be registered with a target group.
Rules
Rules define conditions for forwarding requests from listeners to target groups based on properties like headers, paths, query strings etc.
As shown above, the ALB first checks for incoming requests on listeners and then evaluates rules in priority order to determine routing to appropriate target groups and targets.
Now let‘s explore some of the ways ALBs supercharge your application architectures even further.
10 Killer Benefits and Features
Application Load Balancers unlock a number of powerful capabilities for cloud-hosted apps:
1. Layer 7 Load Balancing
ALBs operate at OSI layer 7 for inspection of application-level packets. This enables intelligent routing based on attributes like HTTP headers, cookies, query strings etc. as opposed to just network and transport layer data.
You can forward requests to different target groups based entirely on application traffic content.
2. Microservices and Container Support
Microservices and containers change deployment topology dynamically. ALBs facilitate this by rapidly modifying target group registrations across shared infrastructure as containers begin and terminate.
Features like priority based load balancing, dynamic host port mapping and integration with orchestrators like Amazon ECS optimize utilization in cluster-based architectures.
3. HTTP/2 and WebSockets Protocols
ALBs accelerate HTTP/2 and WebSocket traffic for significant performance gains:
HTTP/2 Benefits
- Faster page loads with server push
- Multiplexing without head-of-line blocking
- Header compression reduces overhead
- Lower power and data usage
WebSocket Advantages
- Full duplex communication
- Persistent connections
- Minimum proxy buffering
- Great for real-time apps
Supporting these technologies in the load balancer eliminates compatibility issues that backend services would otherwise need to tackle.
4. Security Groups and Access Control
You can secure ALBs using both Security Groups (at the instance-level) as well as Network ACLs at the subnet level. Integrating ALBs with AWS Web Application Firewall provides deep application-layer protection.
Further security measures include:
- SSL/TLS termination
- Disabling unused HTTP methods
- Configuring idle connection timeouts
- Restricting IPs, geo-locations and packet floods
- Mitigating DDoS attacks
- Integrating AWS Shield
- And much more
5. IPv6 and Outposts Support
ALBs allow dual-stack IPv6/IPv4 connectivity to support modern client devices and IP addressing schemes.
You can also use ALBs on AWS Outposts for workloads needing low-latency access to on-premises resources. ALBs offer a consistent hybrid experience and operational model both on cloud and on-prem.
6. Content-Based Request Routing
ALBs route requests dynamically based on a number of HTTP attributes:
- Host: Host header in request
- Path: URIs and pattern matching
- Headers: Any standard or custom headers
- Query Strings: Key-value pairs in URL
- Source: Client source IP CIDR ranges
Match conditions using the above fields and forward traffic in real-time to optimize application performance, scale specific services, and divert requests during maintenance events.
7. Lambda Functions and Containers as Targets
You can execute Lambda functions directly from ALBs to enable gradual modernization towards serverless architectures. HTTP clients access serverless apps transparently without workflow disruption.
Containers register with ALBs using dynamic host port mapping for efficient distribution across shared resources in clusters like Amazon ECS.
8. User Authentication Offloading
With built-in integration capabilities for Amazon Cognito, ALBs can authenticate application end users before requests even hit your backend infrastructure.
Standards support for SAML, LDAP, OIDC and social platforms creates flexibility to integrate with existing identity providers and SSO systems.
9. Elastic Scalability and Availability
ALBs inherently scale request handling capacity up to 125,000 RPS without requiring manual intervention. They also ensure high availability through:
- Instant scaling during traffic spikes
- Automatic failover across AZs
- Health checks finding unhealthy hosts
- Maintaining 100% uptime SLAs
Auto Scaling group integration adds horizontally scaling your backend services based on real-time metrics.
10. Operational Insights
ALBs offer detailed access logging with unique trace IDs injected into requests. Critical data points include:
- Requesting client IP addresses
- Latencies for each processing component
- Security profiles in use
- Bytes sent/received
- And more…
CloudWatch dashboards plot key ALB metrics like active connections, processed bytes, request counts etc. This helps optimize configurations and troubleshoot issues faster.
Analytics tools like Athena can further analyze logs to reveal traffic insights.
By leveraging these features thoughtfully, you can build highly scalable, secure and resilient cloud architectures.
But you may still be wondering…
Why Migrate from Classic Load Balancers?
Classic Load Balancers (CLBs) balance traffic at layers 3 and 4 as opposed to layer 7. So why shift to ALBs given existing infrastructure on CLBs?
More Advanced Traffic Management
- Content-based routing unavailable on CLBs
- Target group-based architecture optimizes backend services better
Improved Security
- Native integration with AWS WAF
- HTTP headers like X-Forwarded-For passed securely
Cloud and Container Native
- Interoperability with emerging compute architectures
- Consistent hybrid experience with AWS Outposts
Operational Insights
- CLBs lack detailed HTTP access logs
- Metrics per service vs aggregate only
Simplified Scaling
- Auto Scaling group integration
- Expand to 125,000 RPS without re-architecting
Enriched Platform
- Growing portfolio of capabilities
- More devops-centric monitoring and automation
Exact migration complexity depends on existing architecture intricacies. Perform extensive testing before decommissioning old infrastructure. Strategies include:
- Set up ALBs parallel to legacy CLBs
- Use weighted routing policies to shift traffic gradually
- Maintain both CLBs and ALBs during transition
- Iterate until full validation and stabilization on ALBs
Ultimately though, embracing ALBs unlocks the true potential of building cloud native applications able to exploit the full breadth of innovations across AWS now and into the future.
Architecture Patterns and Best Practices
So you‘re convinced of the business drivers for adopting application load balancing. How do you translate capabilities into real world solutions?
Here are key considerations for architecting scalable and resilient ALB deployments.
Listeners and Ports
Strategically configure listeners to segment traffic:
- Terminate TLS on listeners to offload HTTPS encryption overhead
- Enable HTTP/2 only where needed as newer clients require it
- Reserve separate ports for WebSockets protocols
- Use TCP for non-HTTP-based database and messaging protocols
- Limit external ingress to 80 and 443 while exposing more internally
Target Groups
- Size target groups for peak capacity needed
- Map business functions to specific groups
- Set deregistration delays to drain inflight requests
- Associate ALB with Auto Scaling groups to scale dynamically
Request Routing
Combine advanced routing techniques:
- Host-based rules for multi-domain hosting
- Path-based rules for microservices
- Headers for canary testing and versioning
- Query strings forsticky sessions
- Redirect actions for staging environments
Security
Take full advantage of encryption, identity federation and firewalling:
- Terminate TLS at the ALB rather than individual services
- Authenticate users externally via social and enterprise identity providers
- Use AWS WAF either integrated or as a firewall sandwich
- Lock down bastion host ingress to SMTP and SSH only
- Restrict access via client source IP ranges
Resiliency and Business Continuity
Assume failure will happen and design for fault tolerance:
- Deploy identical ALBs across multiple AZs
- Set up health check thresholds appropriately
- Configure CloudWatch alarms for signs of trouble
- Implement failover routing across regions
- Plan IP warm-up periods for disaster recovery
Infrastructure Interconnections
Tie together all aspects of your application ecosystem:
- Multi-AZ VPC architectures prevent regional outage impact
- On-premises connectivity for legacy workloads
- Transit Gateways to route between VPCs and VPNs
- Direct Connect for predictable cross-region latency
Following these patterns will help you unlock maximum value from application load balancing for your specific use case by tailoring to functional and non-functional requirements.
Optimizing ALB Configurations
Beyond base architecture, you can further tune ALB deployments for efficiency:
Right-Size Target Groups
- Consolidate related services together
- Segment by production vs non-production
- Resize occasionally as demands change
Connection Reuse
- Use keep-alive timeout > 60 seconds
- Reuse connections with slow-starting targets
Health Checks
- Set path based on application logic
- Use wildcards for dynamic content
- Customize threshold % and intervals
Connection Draining
- Set draining timeout > requests duration
- Disable new requests during shutdown
Auto Scaling
- Scale groups based on RequestsPerTarget
- Add buffer above baseline capacity
Sticky Sessions
- Associate cookies to route users consistently
- Useful for localized content and shopping carts
Request Tracing
- Inject trace fields into app logs
- Correlate log streams back to client
API Gateway Backends
- Point APIs to ALB targets
- Scale effortlessly as traffic volumes increase
Continuous benchmarking and load testing will help uncover further areas for performance and cost improvement over time.
Now let‘s look at some common use cases.
Top 5 ALB Use Cases
Here are typical scenarios where ALBs make a big difference:
Microservices
- Map target groups to individual services
- Scale each one independently
- Route based on path patterns
Containers
- Auto-register ECS containers
- Distribute load across clusters
- Replace hosts during deployments
Multi-Region Resiliency
- Cross-region replication
- Failover routing
- Multi-AZ redundancy
Gradual Serverless Shift
- Register Lambda functions as targets alongside traditional servers
- Transition transparently without architecture overhaul
Single Page Applications
- Accelerate initial page loads
- Offer WebSockets for real-time functionality
Many more applications exist. ALB extensibility caters to custom requirements.
Migrating to ALBs
Follow a phased approach to migration:
Set up in Parallel
Deploy ALBs in same VPCs as Classic ELBs to test subset of traffic.
Weighted Traffic Shifting
Gradually ramp ALB percentage from 0 to 100% via routing policies.
Validate Iteratively
Smoke test functionality, performance, reliability at each stage.
Cutover Eventually
Retire CLBs once ALB testing and metrics look healthy.
Assume Issues
Have rollback plans ready in case unexpected problems appear.
Maintain legacy and modern infrastructure simultaneously during transition to minimize risk.
Get Started Now
We‘ve covered a lot of ground explaining why and how to best leverage Application Load Balancers. Here are some parting thoughts:
-
ALBs offer significant gains in scalability, security and availability of cloud-hosted workloads
-
Advanced traffic steering unlocks innovation in microservices, containers and more
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Migration from Classic ELBs should follow a phased, iterative approach
-
Architecting for failure tolerance and continuous evolution is key
To learn more and get started:
- Review ALB product page
- Dig into technical documentation
- Contact professional services for help
Here‘s wishing you happy load balancing ahead!
