[core] Improve cold startime

[sebsto]

1. Effectively and simply measure cold start time to establish a baseline on a couple of scenario (Hello World, Soto + DynamoDB, AWS SDK + DynamoDB for example)
2. Explore improvements provided by using the static linux musl SDK or the static Amazon Linux 2023 SDK
3. Explore improvements brought by reducing the binary size)
4. Document how to achieve minimum cold start time (this probably won't be the default for the archive plugin)

This is related to

• benchmark: Consider using benchmark #577
• compile for musl: [plugin] add option to compile with the Static Linux SDK instead of docker #332 (and update the CI
• document deployment of OCI images: [plugin] Offer the option to package and deploy using AWS Lambda Container Image Support #193 and [doc] Updated deployment guidance for SAM #485

[sebsto]

Some interesting data about binary size on Amazon Linux 2023.
I used Examples/HelloWorldNoTraits that disables all traits - this is the smallest library size we can have as of today.

➜  HelloWorldNoTraits git:(main) ✗ docker run -it --rm -v $(pwd):/build -w /build swift:6.2-amazonlinux2023 bash -c "swift build -c release --static-swift-stdlib"
[1/1] Planning build
Building for production...
[18/18] Linking MyLambda
Build complete! (39.22s)

➜  HelloWorldNoTraits git:(main) ✗ ls -la .build/aarch64-unknown-linux-gnu/release/MyLambda
-rwxr-xr-x@ 1 stormacq  staff  28102952 Nov 19 19:25 .build/aarch64-unknown-linux-gnu/release/MyLambda

➜  HelloWorldNoTraits git:(main) ✗ docker run -it --rm -v $(pwd):/build -w /build swift:6.2-amazonlinux2023 bash -c "swift build -c release --static-swift-stdlib -Xlinker -s -Xswiftc -Osize" 
[1/1] Planning build
Building for production...
[18/18] Linking MyLambda
Build complete! (34.26s)

➜  HelloWorldNoTraits git:(main) ✗ ls -la .build/aarch64-unknown-linux-gnu/release/MyLambda
-rwxr-xr-x@ 1 stormacq  staff  10645152 Nov 19 19:27 .build/aarch64-unknown-linux-gnu/release/MyLambda

That's a ~62% size reduction.

Cold Start time measurement

Compiled on Amazon Linux 2023.
Deployed with provided.al2023 OS-only Lambda runtime.
This is measured over 10 iterations.
There is no much difference introduced by the file size.

1. No optimisation

➜  HelloWorldNoTraits git:(main) ✗ ls -al lambda.zip 
-rw-r--r--@ 1 stormacq  staff  8140440 Nov 19 19:40 lambda.zip

➜  HelloWorldNoTraits git:(main) ✗ ls -al .build/aarch64-unknown-linux-gnu/release/MyLambda
-rwxr-xr-x@ 1 stormacq  staff  28102952 Nov 19 19:40 .build/aarch64-unknown-linux-gnu/release/MyLambda

  Count: 10
  Average: 81.29ms
  Min: 69.58ms
  Max: 94.56ms

2. optimized binary

➜  HelloWorldNoTraits git:(main) ✗ ls -al lambda.zip
-rw-r--r--@ 1 stormacq  staff  3754204 Nov 19 19:45 lambda.zip

➜  HelloWorldNoTraits git:(main) ✗ ls -al .build/aarch64-unknown-linux-gnu/release/MyLambda
-rwxr-xr-x@ 1 stormacq  staff  10645152 Nov 19 19:45 .build/aarch64-unknown-linux-gnu/release/MyLambda

  Count: 10
  Average: 79.64ms
  Min: 63.67ms
  Max: 90.86ms

Warm start time measurement

  Count: 10
  Average: 2.00ms
  Min: 2ms
  Max: 2ms