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Is there a way to hook in to a build target and ru...
# general
g
Is there a way to hook in to a build target and run some functionality before/afterwards?
w
before is possible by adding a dependency on an 
experimental_shell_command
: https://www.pantsbuild.org/docs/run-shell-commands … but note that the process will run in a sandbox.
after… currently isn’t possible.
g
hmmm, trying to restructure after lambda target build as PEX seems to add 400ms cold start based on the structure
w
ah… sorry. i assumed a particular usecase (testing). you can definitely use an 
experimental_shell_command
to consume a 
pex_binary
and manipulate it.
so something like:
Copy code
pex_binary(name='a', ..)
experimental_shell_command(name='b', dependencies=['a'], ..)
archive(name='c', dependencies=['b'], ..)
…would allow you to create an archive after manipulating a PEX. but feeding a PEX through a script like this loses type information: it’s no longer a PEX from Pants’ perspective
i’m not familiar with whether lambda keeps environments around, but: in the 
venv
execution_mode, latency should be within 50 ms of an existing venv after the first run
g
This is what I'm thinking of following
Seems the package size in lambda doesnt matter as much as how accessible the packages are
w
experimental_shell_command
should be roughly equivalent to 
genrule
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but if there is an alternative layout of a PEX that ends up being significantly faster, reporting an issue on https://github.com/pantsbuild/lambdex/ would be appreciated. i’m not aware of why the alternate layout would be faster (the blog post mentions a different, please-specific reason for doing this)
g
Hard to tell but from what I have seen AWS use some underlying caching mechanism which is why the docker image size doesnt increase cold starts too much for a docker image lambda function. I imagine its the same for Python, so the size matters less and they likely optimize for SAM
h
Is that 400ms when compared to a hand-constructed lambda .zip containing all the same requirements etc?
g
Correct (hand constructed being SAM)
h
Hmm probably we should change our implementation to construct lambdas the same way SAM does (using their CLI even) rather than with lambdex
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