[SAM] Docker Perf on Mac & Root Proxy

[metaskills]

Unfortunately, the SAM CLI project has a few needed enhancements and if you decide to do any local development via the sam local start-api command, it will need to be patched on your local machine. I used the commands below to find the two files needing patching.

$ which sam # Use directory info below in find command.
$ find /usr/local -name container.py | grep samcli
$ find /usr/local -name local_apigw_service.py | grep samcli

Here are the issues we have created on the SAM CLI project. Details on the patches below.

• Add Docker Delegated Consistency to Volume FIXED ✅
• Missing Authentication Token for root path '/' ** FIXED ✅** (Add Docker Delegated Consistency to Volume aws/aws-sam-cli#1046)

Docker Volume Mount Performance on Mac

If you are on a Mac, Docker has a known performance issue when sharing volumes due to the overhead of keeping files in sync. This performance issue means your Rails application could take ~60 seconds to load in development. Thankfully, Docker has tooling in place to help.

Once you found the correct container.py file, make this change below to tell the Docker SDK to mount the volume with both the ro (read-only) option and delegated consistency mode.

@@ -95,7 +95,7 @@
                     # https://docs.docker.com/storage/bind-mounts
                     # Mount the host directory as "read only" inside container
                     "bind": self._working_dir,
-                    "mode": "ro"
+                    "mode": "ro,delegated"
                 }
             },
             # We are not running an interactive shell here.

Fixing Root SAM Local Proxy Paths

We need our API Gateway to use both a root path and a greedy proxy path to forward to Rails in development. SAM has a feature compatibility bug where it forces static file hosting on the root path. Once you found the correct local_apigw_service.py file, make the change below to disable static public directory assets on the root path. Don't worry, Rails & Rack will serve your static files automatically instead.

@@ -71,7 +71,7 @@
         """

         self._app = Flask(__name__,
-                          static_url_path="",  # Mount static files at root '/'
+                          static_url_path=None,  # Mount static files at root '/'
                           static_folder=self.static_dir  # Serve static files from this directory
                           )

[metaskills]

This has been resolved (aws/aws-sam-cli#1046) and is also moot when we use our own Docker images like this Cookiecutter (https://technology.customink.com/blog/2020/03/13/using-aws-sam-cookiecutter-project-templates-to-kickstart-your-ambda-projects/) in future Lamby templates.