AWS ALB Websocket Support: Everything You Need to Know

AWS Application Load Balancer (ALB) is a powerful tool that enables users to distribute incoming traffic to multiple targets, including EC2 instances, containers, and Lambda functions. In addition to the traditional HTTP and HTTPS protocols, ALB also supports the WebSocket protocol, allowing users to build real-time communication applications that require bidirectional communication between the client and the server. In this article, we will explore everything you need to know about AWS ALB WebSocket support, including its benefits, limitations, and best practices.

What is WebSocket?

WebSocket is a protocol that enables bidirectional communication between the client and the server over a single, long-lived connection. Unlike HTTP, which is a request-response protocol, WebSocket allows the server to push data to the client without waiting for a request. WebSocket is ideal for building real-time communication applications, such as chat applications, online gaming, and collaborative editing tools.

What is AWS Application Load Balancer (ALB)?

AWS Application Load Balancer (ALB) is a load balancing service that distributes incoming traffic across multiple targets, such as EC2 instances, containers, and Lambda functions. ALB supports the traditional HTTP and HTTPS protocols, as well as the WebSocket protocol. ALB provides advanced features, such as content-based routing, path-based routing, and host-based routing, which enable users to route traffic to different targets based on the content, path, or host of the incoming request. ALB also provides health checks, which automatically detect and route traffic away from unhealthy targets.

What are the Benefits of Using AWS ALB for WebSocket?

There are several benefits of using AWS ALB for WebSocket:

1. Scalability: ALB enables users to distribute incoming WebSocket traffic across multiple targets, allowing them to handle a large volume of WebSocket connections. ALB also provides auto-scaling, which automatically adjusts the number of targets based on the incoming traffic.
2. Security: ALB provides SSL/TLS termination, which enables users to offload SSL/TLS encryption and decryption from their targets. ALB also provides access logs, which enable users to monitor and analyze WebSocket traffic.
3. Flexibility: ALB provides advanced routing features, which enable users to route WebSocket traffic based on the content, path, or host of the incoming request. ALB also supports multiple protocols, such as HTTP, HTTPS, and WebSocket, allowing users to build hybrid applications that require different protocols.
4. Cost-effectiveness: ALB is a pay-as-you-go service, which means that users only pay for the traffic that they receive. ALB also provides cost-saving features, such as connection multiplexing, which enables users to handle multiple WebSocket connections over a single TCP connection.

What are the Limitations of Using AWS ALB for WebSocket?

There are several limitations of using AWS ALB for WebSocket:

1. Connection limits: ALB imposes a limit on the number of WebSocket connections that can be handled by a single target. The limit depends on the instance size and the WebSocket message size. Users can increase the limit by using larger instances or by reducing the WebSocket message size.
2. Latency: ALB introduces additional latency to WebSocket traffic due to the SSL/TLS termination and the load balancing process. The latency depends on the size of the WebSocket message and the number of targets. Users can reduce the latency by using smaller WebSocket messages and by optimizing their targets.
3. WebSocket protocol limitations: ALB supports the WebSocket protocol up to version 13, which is the latest version as of this writing. ALB does not support WebSocket extensions, such as compression or multiplexing. ALB also does not support the WebSocket subprotocol negotiation.

What are the Best Practices for Using AWS ALB for WebSocket?

There are several best practices for using AWS ALB for WebSocket:

1. Use SSL/TLS encryption: ALB provides SSL/TLS termination, which enables users to offload SSL/TLS encryption and decryption from their targets. This helps to reduce the load on the targets and to improve the security of the WebSocket traffic.
2. Use content-based routing: ALB provides content-based routing, which enables users to route WebSocket traffic based on the content of the incoming request. This helps to improve the scalability and flexibility of the WebSocket application.
3. Use health checks: ALB provides health checks, which automatically detect and route traffic away from unhealthy targets. This helps to improve the availability and reliability of the WebSocket application.
4. Use connection multiplexing: ALB provides connection multiplexing, which enables users to handle multiple WebSocket connections over a single TCP connection. This helps to reduce the number of TCP connections and to improve the performance of the WebSocket application.
5. Optimize WebSocket message size: ALB imposes a limit on the size of WebSocket messages that can be handled by a single target. Users can optimize their WebSocket message size by reducing the payload and by compressing the data.

FAQs

What is the difference between ALB and ELB?

Amazon Elastic Load Balancer (ELB) is a previous version of the AWS load balancing service, which has been replaced by Application Load Balancer (ALB) and Network Load Balancer (NLB). ELB supports the traditional HTTP and HTTPS protocols, but it does not support the WebSocket protocol. ALB provides advanced features, such as content-based routing, path-based routing, and host-based routing, which are not available in ELB. NLB provides low-latency, high-throughput, and connection-oriented load balancing for TCP, UDP, and TLS traffic.

What is the WebSocket message size limit?

The WebSocket message size limit depends on the instance size and the WebSocket message size. For example, a t2.micro instance can handle up to 1,000 WebSocket connections with a message size of up to 128 KB. Users can increase the limit by using larger instances or by reducing the WebSocket message size.

What is the ALB pricing model?

ALB is a pay-as-you-go service, which means that users only pay for the traffic that they receive. ALB charges based on the number of processed requests and the amount of data transferred. The pricing varies by region and depends on the usage pattern and the traffic volume. Users can estimate their monthly bill using the AWS pricing calculator.

What is the ALB WebSocket connection limit?

The ALB WebSocket connection limit depends on the instance size and the WebSocket message size. For example, a t2.micro instance can handle up to 1,000 WebSocket connections with a message size of up to 128 KB. Users can increase the limit by using larger instances or by reducing the WebSocket message size.

What is the WebSocket protocol version supported by ALB?

ALB supports the WebSocket protocol up to version 13, which is the latest version as of this writing. ALB does not support WebSocket extensions, such as compression or multiplexing. ALB also does not support the WebSocket subprotocol negotiation.