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Comment by philliphaydon | Hacker News Reader

One thing is that ALB to Lambda restrictions suck.

Lambdas have a 6mb response size. Api gateway has a 10mb response size. If you go ALB to Lambda. And your response is over 1mb. Your response will fail. Because the ALB team decided to introduce a random 1mb limit, not document it as a limitation, and added it to their trouble shooting notes instead.

So if you need to return a small PDF or something from a lambda via ALB. Good luck.

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FYI for anyone reading, the expected architecture is to return the URL to an S3 object that is your larger than 1mb response.

The reason they do this is to keep the alb running efficiently by not having to architect for random large responses.

The problem I have is, is the limit is less than the limit imposed by Lambda itself. Which is less than the limit imposed by API Gateway.

API Gateway: 10mb

Lambda: 6mb

ALB: 1mb

Yet if your target is an ec2 instance, there's no limit on the load balancer. So IMO the limit for a lambda target should be the limit imposed by Lambda itself. 6mb.

While I'm not disputing the limit numbers or whatever hardship they might cause, it's worth noting that this is a basic limitation of the original Lambda model and maybe FaaS in general. The capability comes from running a giant pseudo-infinite mesh of isolated execution environments that load your code and execute on demand, while having to buffer both the request and response to make sure clients are protected from the details. This buffering means that size of the buffer will always be limited - the team managing might make the buffers bigger based on experience, but it's not a solved problem.

ALB to containers or servers is a different beast - here the entire request and response need not be buffered at all (there might still be a very small buffer, mostly negligible), so streaming responses, websockets etc become possible.

We use lambda to resize images, so we do push against these limits a bit, but it's a fair tradeoff for the advantages - no worries about CPU throttling from too many requests, no waiting for servers to start for spiky loads etc.

Lambda was not designed for request/response. It’s an event driven service. Wrapping API gateway around it is an architectural blunder, and leads to folks like the GP wondering why their use case is a shitty fit.

Why is request/response not a fit for an event driven service in your view? A lot of request/response server apps are written using the event model.

Trying to build synchronous out of asynchronous requires state machines, buffering, and overallocation of resources. It’s the enemy of scale.

The two styles are an impedance mismatch.

There is nothing inherently asynchronous about the Lambda product, unless you’re talking about the Node.js runtime and even then that’s more about Node than about Lambda.

Each Lambda invocation gets a dedicated VM for the duration of the request. It is a great match for synchronous code.

That is a mis-statement. Lambda executes functions in response to events. It is totally asynchronous with regards to its execution triggers.

Lambda does reuse VMs, so I hope you aren’t relying on containers being discarded for any integrity or security outcomes.

All the responses in this thread illustrate to me that AWS needs to put more effort into socialising how the product works. Since I was physically in the room for Lambda’s AWS internal launch this is twice disappoint because the technical messaging then was very clear and compelling.

Lambda is natively http based, no? Like all aws apis. It's just that it only speaks it's own json protocol, not generic web.

Also request/response is not inherently synchronous or asynchronous. It's just a protocol design pattern.

Buffering, overcommit, etc are also kust normal facts of life in both sync and async messaging.

No, it it natively event driven. Don’t confuse the control plane for the operational.

Request/response is fundamentally synchronous. If you want to nitpick about other layers not blocking, that’s missing the wood for the trees.

I would read a deep dive blog post about this.

“function as a service” absolutely does need to support request/response as a primary use case.

It is documented, at least on this page:

https://docs.aws.amazon.com/elasticloadbalancing/latest/appl...

Right at the top of the page, underneath the header "Limits"

> The maximum size of the response JSON that the Lambda function can send is 1 MB.

Ah this must be relatively new. The only documentation I could find or AWS Support Business Support / Lambda team could give me was a link to:

https://docs.aws.amazon.com/elasticloadbalancing/latest/appl...

Which I complained about because it wasn't mentioned as lambda as a target docs. I guess they amended it.

git blame suggests the change was made 15 months ago, though that doesn't take it to account time to publish. Which I guess just goes to show that it can be tough to find information on the docs, despite them been relatively decent as far as docs go (in my opinion).

Somebody has a war story

War stories are the best part of HN.

That's pretty damning, lots of innocent REST messages can be more than 1MB. Can you have larger bodies in chunked encoding?

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