Application Load Balancer (ALB)

Hello Everyone

Welcome to CloudAffaire and this is Debjeet.

In the last blog post, we have an introduction to AWS Elastic Load Balancing.

https://cloudaffaire.com/elastic-load-balancing-elb/

In this blog post, we will start with the Application Load Balancer.

Application Load Balancer (ALB):

An Application Load Balancer functions at the application layer, the seventh layer of the Open Systems Interconnection (OSI) model. After the load balancer receives a request, it evaluates the listener rules in priority order to determine which rule to apply, and then selects a target from the target group for the rule action. You can configure listener rules to route requests to different target groups based on the content of the application traffic. Routing is performed independently for each target group, even when a target is registered with multiple target groups.

You can add and remove targets from your load balancer as your needs change, without disrupting the overall flow of requests to your application. Elastic Load Balancing scales your load balancer as traffic to your application changes over time. Elastic Load Balancing can scale to the vast majority of workloads automatically.

Application Load Balancer Components:

Listener: A listener checks for connection requests from clients, using the protocol and port that you configure. The rules that you define for a listener determine how the load balancer routes requests to its registered targets. Each rule consists of a priority, one or more actions, and one or more conditions. When the conditions for a rule are met, then its actions are performed. You must define a default rule for each listener, and you can optionally define additional rules.

Targets: Each target group routes requests to one or more registered targets, such as EC2 instances, using the protocol and port number that you specify. You can register a target with multiple target groups. You can configure health checks on a per target group basis. Health checks are performed on all targets registered to a target group that is specified in a listener rule for your load balancer.

Application Load Balancer Features:

Application Load Balancer operates at the request level (layer 7), routing traffic to targets – EC2 instances, containers, IP addresses and Lambda functions based on the content of the request. Ideal for advanced load balancing of HTTP and HTTPS traffic, Application Load Balancer provides advanced request routing targeted at delivery of modern application architectures, including microservices and container-based applications. Application Load Balancer simplifies and improves the security of your application, by ensuring that the latest SSL/TLS ciphers and protocols are used at all times.

1. Layer-7 Load Balancing: You can load balance HTTP/HTTPS applications and use layer 7-specific features, such as X-Forwarded-For headers.
2. HTTPS Support: An Application Load Balancer supports HTTPS termination between the clients and the load balancer. Application Load Balancers also offer management of SSL certificates through AWS Identity and Access Management (IAM) and AWS Certificate Manager for pre-defined security policies.
3. Server Name Indication (SNI): Server Name Indication (SNI) is an extension to the TLS protocol by which a client indicates the hostname to connect to at the start of the TLS handshake. The load balancer can present multiple certificates through the same secure listener, which enables it to support multiple secure websites using a single secure listener. Application Load Balancers also support a smart certificate selection algorithm with SNI. If the hostname indicated by a client matches multiple certificates, the load balancer determines the best certificate to use based on multiple factors including the capabilities of the client.
4. IP addresses as Targets: You can load balance any application hosted in AWS or on-premises using IP addresses of the application backends as targets. This allows load balancing to an application backend hosted on any IP address and any interface on an instance. Each application hosted on the same instance can have an associated security group and use the same port. You can also use IP addresses as targets to load balance applications hosted in on-premises locations (over a Direct Connect or VPN connection), peered VPCs and EC2-Classic (using ClassicLink). The ability to load balance across AWS and on-prem resources helps you migrate-to-cloud, burst-to-cloud or failover-to-cloud.
5. Lambda functions as Targets: Application Load Balancers support invoking Lambda functions to serve HTTP(S) requests enabling users to access serverless applications from any HTTP client, including web browsers. You can register Lambda functions as targets for a load balancer and leverage the support for content-based routing rules to route requests to different Lambda functions. You can use an Application Load Balancer as a common HTTP endpoint for applications that use servers and serverless computing. You can build an entire website using Lambda functions or combine EC2 instances, containers, on-premises servers and Lambda functions to build applications.
6. High Availability: An Application Load Balancer requires you to specify more than one Availability Zone. You can distribute incoming traffic across your targets in multiple Availability Zones. An Application Load Balancer automatically scales its request handling capacity in response to incoming application traffic.
7. Security Features: When using Amazon Virtual Private Cloud (VPC), you can create and manage security groups associated with Elastic Load Balancing to provide additional networking and security options. You can configure an Application Load Balancer to be Internet facing or create a load balancer without public IP addresses to serve as an internal (non-internet-facing) load balancer.
8. Content-based Routing: If your application is composed of several individual services, an Application Load Balancer can route a request to a service based on the content of the request.
   1. Host-based Routing: You can route a client request based on the Host field of the HTTP header allowing you to route to multiple domains from the same load balancer.
   2. Path-based Routing: You can route a client request based on the URL path of the HTTP header.
   3. HTTP header-based routing: You can route a client request based on the value of any standard or custom HTTP header.
   4. HTTP method-based routing: You can route a client request based on any standard or custom HTTP method.
   5. Query string parameter-based routing: You can route a client request based on query string or query parameters.
   6. Source IP address CIDR-based routing: You can route a client request based on source IP address CIDR from where the request originates.
9. Containerized Application Support: Application Load Balancer provides enhanced container support by load balancing across multiple ports on a single Amazon EC2 instance. Deep integration with the Amazon EC2 Container Service (ECS), provides a fully-managed container offering. ECS allows you to specify a dynamic port in the ECS task definition, giving the container an unused port when it is scheduled on the EC2 instance. The ECS scheduler automatically adds the task to the load balancer using this port.
10. HTTP/2 Support: HTTP/2 is a new version of the HyperText Transfer Protocol (HTTP) that uses a single, multiplexed connection to allow multiple requests to be sent on the same connection. It also compresses header data before sending it out in binary format and supports SSL connections to clients.
11. WebSockets Support: WebSockets allows a server to exchange real-time messages with end-users without the end users having to request (or poll) the server for an update. The WebSockets protocol provides bi-directional communication channels between a client and a server over a long-running TCP connection.
12. Native IPv6 Support: Application Load Balancers support native Internet Protocol version 6 (IPv6) in aVPC. This will allow clients to connect to the Application Load Balancer via IPv4 or IPv6.
13. Sticky Sessions: Sticky sessions are a mechanism to route requests from the same client to the same target. Application Load Balancer supports sticky sessions using load balancer generated cookies. If you enable sticky sessions, the same target receives the request and can use the cookie to recover the session context. Stickiness is defined at a target group level.
14. Health Checks: An Application Load Balancer routes traffic only to healthy targets. With an Application Load Balancer, you get improved insight into the health of your applications in two ways: (1) health check improvements that allow you to configure detailed error codes from 200-499. The health checks allow you to monitor the health of each of your services behind the load balancer; and (2) new metrics that give insight into traffic for each of the services running on an EC2 instance.
15. Operational Monitoring: Amazon CloudWatch reports Application Load Balancer metrics such as request counts, error counts, error types, and request latency.
16. Logging: You can use the Access Logs feature to record all requests sent to your load balancer, and store the logs in Amazon S3 for later analysis. The logs are compressed and have a gzip file extension. The compressed logs save both storage space and transfer bandwidth and are useful for diagnosing application failures and analyzing web traffic. You can also use AWS CloudTrail to record Application Load Balancer API calls for your account and deliver log files. The API call history enables you to perform security analysis, resource change tracking, and compliance auditing.
17. Delete Protection: You can enable deletion protection on an Application Load Balancer to prevent it from being accidentally deleted.
18. Request Tracing: The Application Load Balancer injects a new custom identifier “X-Amzn-Trace-Id” HTTP header on all requests coming into the load balancer. Request tracing allows you to track a request by its unique ID as the request makes its way across various services that make up the your websites and distributed applications. You can use the unique trace identifier to uncover any performance or timing issues in your application stack at the granularity of an individual request.
19. Web Application Firewall: You can now use AWS WAF to protect your web applications on your Application Load Balancers. AWS WAF is a web application firewall that helps protect your web applications from common web exploits that could affect application availability, compromise security, or consume excessive resources.
20. Slow Start Mode with Load-Balancing Algorithm: Application Load Balancer supports a round-robin load-balancing algorithm. Additionally, Application Load Balancer supports a slow start mode with the round-robin algorithm that allows you to add new targets without overwhelming them with a flood of requests. With the slow start mode, targets warm up before accepting their fair share of requests based on a ramp-up period that you specify. Slow start is very useful for applications that depend on cache and need a warm-up period before being able to respond to requests with optimal performance.
21. User Authentication: You can offload the authentication functionality from your apps into Application Load Balancer. Application Load Balancer will securely authenticate users as they access cloud applications. Application Load Balancer is seamlessly integrated with Amazon Cognito, which allows end users to authenticate through social identity providers such as Google, Facebook, and Amazon, and through enterprise identity providers such as Microsoft Active Directory via SAML or any OpenID Connect-compliant identity provider (IdP). If you already have a custom IdP solution that is OpenID Connect-compatible, Application Load Balancer can also authenticate enterprise users by directly connecting with your identity provider.
22. Redirects: Application Load Balancer can redirect an incoming request from one URL to another URL. This includes the capability to redirect HTTP requests to HTTPS requests, which allows you to meet your compliance goal of secure browsing, while being able to achieve better search ranking and SSL/TLS score for your site. You can also use redirects to send users to a different web site; for example, redirecting from an old version of an application to a new version.
23. Fixed Response: Application Load Balancer can control which client requests are served by your applications. This enables you to respond to incoming requests with HTTP error response codes and custom error messages from the load balancer itself, without forwarding the request to the application.

Hope you have enjoyed this article, In the next blog post, we will create our 1^st Application Load Balancer.

To get more details on AWS ELB, please refer below AWS documentation

https://docs.aws.amazon.com/elasticloadbalancing/index.html