Name the cached images to make it easier to clean up the cached images

README.md

@@ -212,3 +212,10 @@ It will process the same as `docker`'s `--volume` option, `rocker --volume` take
 - 2nd field: (optional) the path where the file or directory is mounted in the container.
    - If only the 1st field is supplied, same value as the 1st field will be populated as the 2nd field.
 - 3rd field: (optional) bind propagation as `ro`, `z`, and `Z`. See [docs.docker.com](https://docs.docker.com/storage/bind-mounts/) for further detail.
+
+
+## Helpful tips
+
+Clean up the rocker cache
+
+    `docker images | grep rocker_cache | awk '{ printf $1":"$2; print"" }' | xargs docker rmi`

src/rocker/core.py

@@ -14,6 +14,7 @@
 
 from collections import OrderedDict
 import io
+from hashlib import md5
 import os
 import re
 import sys
@@ -225,8 +226,15 @@ def build(self, **kwargs):
             arguments['pull'] = kwargs.get('pull', False)
             image_name = kwargs.get('image_name', None)
             if image_name:
-                print(f"Running docker tag {self.image_id} {image_name}")
                 arguments['tag'] = image_name
+            else:
+                kwhash = self.get_argument_hash(kwargs)
+                #TODO(tfoote) Only flag extensions in the image (aka skip runtime only)
+                tag = 'rocker_cache:' + kwargs.get('image', '').replace(':', '_') + '_extensions__' + '_'.join([x.name for x in self.active_extensions]) + '__arghash' + str(kwhash)
+                arguments['tag'] = tag
+
+            print(f"{kwargs} Generated Image Tagged: {tag}")
+
             print("Building docker file with arguments: ", arguments)
             try:
                 self.image_id = docker_build(
@@ -243,6 +251,15 @@ def build(self, **kwargs):
                 print("Docker build failed\n", ex)
                 return 1
 
+    def get_argument_hash(self, kwargs):
+        """ Compute the has of the arguments excluding elements not included
+        in the image such as the command
+        """
+        # TODO(tfoote) flag specific keywords as being in the image vs only runtime
+        invariant = kwargs
+        invariant.pop('command')
+        return md5(str(invariant).encode()).hexdigest()
+
     def get_operating_mode(self, args):
         operating_mode = args.get('mode')
         # Default to non-interactive if unset