docker: do not remove build dep which might be needed by extension

[yugangw-msft]

Fix #8284
Note: the image size increases from 497MB to 666MB, but extension installation must work so build dep has to stay

• The PR has modified HISTORY.rst describing any customer-facing, functional changes. Note that this does not include changes only to help content. (see Modifying change log).

• I adhere to the Command Guidelines.

[tjprescott]

But if an extension has a dependency, shouldn't the extension declare its own dependency so that it is installed? We can't expect the CLI to know all the dependencies an extension might need and carry them.

[tjprescott]

I might be misunderstanding the issue, but we should consult with @williexu

[marstr]

I agree with @tjprescott. Indiscriminately adding build dependencies will bloat our image more than in helps support extensions. We should continue to work with the authors of extensions that aren't working to ensure they've accurately described all of their dependencies.

[yugangw-msft]

The workaround for now is:
docker run -it microsoft/azure-cli sh -c "apk add --no-cache --virtual .build-deps gcc make openssl-dev libffi-dev musl-dev && bash"

There is no simple patch can be done at the extension end, afaik. To maintain the sandbox model, CLI installs all dependencies to extension’s own folder, which means the build tools must be around. This also means, in a nutshell, that any extensions has azure-mgmt-* or msrest-azure called out in setup.py will be broken. For context, most extensions don’t have any dependencies specified at all in setup.py, guess that is why they are still surviving.

For the payload increase of not removing the build deps, I would not worry too much, once this issue #7387 gets addressed, we would sure find some balances back.

[marstr]

We chatted about this offline for quite a while. We agreed that being able to install extensions is enough of a core-scenario that it's worth increasing the size of the image to facilitate it.