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feat(rust): add second example using non-op internal extension, expand README #19

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@jlizen jlizen commented May 4, 2025 •
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Issue #, if available:
Closes: #1

Description of changes:
The current Rust example uses an external extension, CloudWatch Lambda Insights. It works fine, but it adds overhead if you don't need the extension since it requires a standalone process running. It also adds billing costs / cold start / etc.

Adding an additional example that uses an internal extension instead. I updated the README to discuss the difference between both.

Related PR on the aws-lambda-rust-runtime side:

Testing
Each example has its own SAM template. I tested each end to end including deploy, sending traffic, validating the graceful shutdown in logs, etc. The two examples can co-exist in the same account without issue.

Note that graceful shutdown is not currently testable locally via cargo lambda watch, ref:
cargo-lambda/cargo-lambda#850

Internal extension logs:

INIT_START Runtime Version: provided:al2023.v90	Runtime Version ARN: arn:aws:lambda:us-east-1::runtime:afd9ea1d72c8135b0bcfe7ebce16e06002647cb9e5195edeb536e21e1ef6d259
EXTENSION	Name: no-op	State: Ready	Events: [INVOKE]
START RequestId: 69e2cff4-7740-4d6e-bc2f-4f317214fba8 Version: $LATEST
END RequestId: 69e2cff4-7740-4d6e-bc2f-4f317214fba8
REPORT RequestId: 69e2cff4-7740-4d6e-bc2f-4f317214fba8	Duration: 37.74 ms	Billed Duration: 62 ms	Memory Size: 128 MB	Max Memory Used: 16 MB	Init Duration: 23.90 ms	
[runtime] SIGTERM received
[runtime] Graceful shutdown in progress ...
[runtime] Graceful shutdown completed

External extension logs:

INIT_START Runtime Version: provided:al2023.v90	Runtime Version ARN: arn:aws:lambda:us-east-1::runtime:afd9ea1d72c8135b0bcfe7ebce16e06002647cb9e5195edeb536e21e1ef6d259
LOGS	Name: cloudwatch_lambda_agent	State: Subscribed	Types: [Platform]
EXTENSION	Name: cloudwatch_lambda_agent	State: Ready	Events: [SHUTDOWN, INVOKE]
START RequestId: b90265f5-f87e-4642-a1a2-2f77f4ca224e Version: $LATEST
END RequestId: b90265f5-f87e-4642-a1a2-2f77f4ca224e
REPORT RequestId: b90265f5-f87e-4642-a1a2-2f77f4ca224e	Duration: 65.05 ms	Billed Duration: 153 ms	Memory Size: 128 MB	Max Memory Used: 26 MB	Init Duration: 87.50 ms	
[runtime] SIGTERM received
[runtime] Graceful shutdown in progress ...
[runtime] Graceful shutdown completed

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jlizen commented May 6, 2025

A couple updates:

I do have a PR out to tokio for biased support in try_join:
tokio-rs/tokio#7307

If we merge this with the TODO still in place, I can circle back and cut it over once it lands.

I also have cargo lambda watch working locally against the example with this fix in place:
cargo-lambda/cargo-lambda#853

bnusunny
bnusunny reviewed May 6, 2025
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jlizen commented May 6, 2025 •
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Capturing some offline discussion with bnusunny@:

@jlizen we can make it even simpler: add a shutdown hook in rust runtime, so it will be dead simple to handle graceful shutdown. Under the hood, the rust runtime can register a dummy internal extension.

Yeah I was thinking the same. I'll poke around with that tomorrow.
I was previously concerned about overhead, since if you are forced to subscribe to invokes, that means that the extension future will be woken for each event. Which means that you probably want to call it within try_join!, which starts to be pretty messy to abstract away from the user from an api perspective.
But as you correctly pointed out, there is no need to subscribe to events. So, it should be fine to just spawn a task to drive the no-op extension in the background.

I'm fine to put this PR on hold in anticipation of such a feature, if preferred. Or, I can backport usage of that new API once it is available. Up to you.

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jlizen commented May 6, 2025 •
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Graceful shutdown hook PR: awslabs/aws-lambda-rust-runtime#982

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feat(rust): add second example using non-op internal extension with n…
1b4a953 
…ew lambda-runtime helper, expand README, clean up cargo imports
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jlizen commented May 29, 2025

@bnusunny this PR has been updated:

  • cut internal extension example over to use the new graceful shutdown helper in lambda-runtime >= 0.14.0
  • tweak README to instead guide readers to that helper as the easiest path
  • clean up a lot of vestigial Cargo.toml imports to reduce noise
  • cut over to using lambda-runtime's default tracing subscriber helper, also to reduce noise

I could see an argument for ditching the external extension example entirely, but it's kind of nice to have somewhere where we show the signal handling inline in Rust code. Since, it is tucked away via the helper. I think probably including both is still nice.

I've tested both internal and external extensions end to end, including sam build + deploy, invoking API Gateway via curl, and validating that cloudwatch logs shows the graceful shutdown hook firing.

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jlizen commented May 29, 2025

Note that the README links to the docs.rs link for the graceful shutdown handler function, which is not yet published. We will need to merge awslabs/aws-lambda-rust-runtime#1000 first and cut a new release. At that point, the link should be good.

So, this should not be merged before that release goes out. I'll explicitly validate that the link is working at that time and drop a note here as such.

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Feature: A dummy Rust Lambda extension
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