Using pex in combination with S3 for storing the pex files, we built a system where the fast path avoids the overhead of building and launching Docker images.Our system works like this: when you commit code to GitHub, the GitHub action either does a full build or a fast build depending on if your dependencies have changed since the previous deploy. We keep track of the set of dependencies specified in setup.py and requirements.txt.For a full build, we build your project dependencies into a deps.pex file and your code into a source.pex file. Both are uploaded to Dagster cloud. For a fast build we only build and upload the source.pex file.In Dagster Cloud, we may reuse an existing container or provision a new container as the code server. We download the deps.pex and source.pex files onto this code server and use them to run your code in an isolated environment.