Allow specifying docker container in which to build code

Describe your idea/feature/enhancement

Sometimes with Python code one requires compiling packages that rely on C libraries. For example, trying to install mysqlclient in the default container will result in an error.

A way to overcome this issue, is to create a new Docker image, based on the lambci/lambda:build-python2.7 one, that will have mysql-devel and python-devel installed in it, and use it when running sam build -u.

Proposal

An obvious solution is just to provide an optional flag, e.g.

sam build --use-container --docker-image lambci/lambda:my-awesome-image

Additional Details

I don’t know enough about the SAM CLI infra to say, but if possible, it would be even better if one could provide a Dockerfile in the template.

[jfuss]

@prcongithub You could build the image locally, retag it as the image we download, and then pass --skip-pull-image.

[zoellner]

@simlu no, I’m still building things with the old containers