Menu
AWS comes with a service called Application Load Balancer and it could be a trigger to a lambda function. The way to call such a lambda function is by sending an HTTP/HTTPS request to ALB.
Now my question is how this is any different from using the API Gateway? And when should one use ALB over API Gateway (or the way around)?
834
We recently wrote about whether API Gateway can act as a Load Balancer. The answer is yes and, in many cases, they are substitutes for each other.
Load Balancing: The API Gateway can work as a load balancer to handle requests in the most efficient manner. It can keep a track of the request load it has sent to different nodes of a particular service. A gateway could be intelligent enough to balance load between different nodes of a particular service.
@whiteSkar You can put loadbalancers before and/or after apiGateways. These are terminologies with their functionalities, how you want to place them depends on the architrecture. If you place before apiGateway, you are effectively balancing the load that goes to apiGateway.
Both ALB and API Gateway can scale to meet massive demand. However, API Gateway by default has a soft limit of 10,000 Requests per Second (RPS) per AWS region per account. (Customers can raise that limit by request.) By contrast, ALB has no pre-set request rate limit.
One of the biggest reasons we use API gateway in front of our lambda functions instead of using an ALB is the native IAM (Identity and Access Management) integration that API GW has. We don't have to do any of the identity work ourselves, it's all delegated to IAM, and in addition to that, API GW has built-in request validation including validation of query string parameters and headers. In a nutshell, there are so many out of the box integrations what come with API GW, you wind up having to do a lot more work if you go the route of using an ALB.
197
It seems that the request/response limit is lower when using ALB, and WebSockets are not supported:
The maximum size of the request body that you can send to a Lambda function is 1 MB. For related size limits, see HTTP Header Limits.
The maximum size of the response JSON that the Lambda function can send is 1 MB.
WebSockets are not supported. Upgrade requests are rejected with an HTTP 400 code.
See: https://docs.aws.amazon.com/elasticloadbalancing/latest/application/lambda-functions.html
Payload limit with API Gateway is discussed here: Request payload limit with AWS API Gateway
Also the article already mentioned by @matesio provides information about additional things to consider when choosing between ALB and API Gateway.
Notable tweet referenced in the mentioned article:
If you are building an API and want to leverage AuthN/Z, request validation, rate limiting, SDK generation, direct AWS service backend, use #APIGateway. If you want to add Lambda to an existing web app behind ALB you can now just add it to the needed route.
(From: Dougal Ballantyne, the Head of Product for Amazon API Gateway)
21
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With
