Hi. I've got a qustion regarding accessing binaries installed in venv from outside pex. We're distributing docker images, built using pants, with .pexes inside, and deploying them on k8s cluster. Recently we wanted to start using celery, but we have to figure out a way to do liveliness checks in kubernetes. In order to do that, we have to invoke a celery command, namely

celery -A path.to.module inspect ping

. The problem here is that

celery

is a part of the .pex file, and it is unclear how to find it and execute it. One way to just find the binary would be to package the pexes in

execution_mode="venv"

, set

PEX_ROOT

to a known location and then to use

source $PEX_ROOT/venvs/s/*/venv/bin/activate

This way I can reach the binary. But the problem remains, because I can't reach the module I need (it is in user code). I suppose I'd also need to set up PYTHONPATH. Another way to reach the binary would be to just install

celery

itself separately in the system python distribution, but I would still need to reach the user code binary. Both the solutions seem like a lot of hackery and I'm not even sure if it's possible to pull any of them off. Is there an easier way to achieve this - accessing venv binaries without running the pex file itself? Or maybe you can override the entrypoint when running venv. Or maybe there is a better way to package docker images? Any help would be much appreciated

If you follow this example: https://pex.readthedocs.io/en/v2.1.107/recipes.html#pex-app-in-a-container You get a venv at

/myapp

. Running

/myapp/pex

runs the PEX entry point, but you can also run any of the

/myapp/bin/<console script>

scripts the distributions in your PEX provide.

That's fantastic, looks exactly like what I was looking for. Thank you so much 🙂

For those times when you can't pre-install a venv and you're stuck with a PEX file, you might be able to use conscript instead as your entry point to get a

busybox

-alike: https://pypi.org/project/conscript/

This works well, thank you. I have one more question regarding the blogpost. I tried to follow it to the very last configuration (deps and srcs split into 2 pexes). One minor difference in my setup is that I'd like to have the

script

field set in the

srcs

pex. I end up with this error though

pex.pex_builder.PEXBuilder.InvalidExecutableSpecification: Could not find script 'celery' in any distribution  within PEX!

It is reasonable, I excluded the requirements, but I know it will be there in the final Docker image. If I leave the script field only in the

deps

pex, it gets overwritten and the entrypoint ends up being python. Is there any way around it or do I have to resort to the first configuration with multi-stage build but single pex?

Hrm, yeah the split PEX optimization is a Pants-side hack and it doesn't cover all cases. I think you'd need to leave off the entry point & script for both

pex_binary

targets forming the split; then in the docker image set

PEX_SCRIPT

(which corresponds to

pex_binary.script

) or

PEX_MODULE

(which corresponds to

pex_binary.entry_point

). I personally don't like this at all, I'd rather have a pex_binary target in my BUILD that I can test and know the final PEX in the Docker image will work the same as. A bit too many moving parts for my taste - but it should work.

It sure does feel a bit hacky. Anyway, I think the standard solution will be good enough for us. Thank you very much for all your help