Implemented squash layer for SDK container image (#27)

* Added squash layer to decrease number of image layers,
* Modified regex to only remove the first appearance of `FROM` in a Dockerfile
* Provide current base layer `as base_container_name` inside Dockerfiles

Author: matthiasb85

builder/build_container.py

@@ -64,9 +64,9 @@ def _build_container(self, name: str, path: str) -> None:
             gid = self.gid
 
 
-        # Replace FROM with layer before.
-        command = f'echo "FROM {self.base_container_name}" > Dockerfile.tmp; ' \
-            'sed \'/FROM /d\' Dockerfile >> Dockerfile.tmp'
+        # Replace first FROM with previous layer.
+        command = f'echo "FROM {self.base_container_name} as base_container_name" > Dockerfile.tmp; ' \
+            'sed \'0,/FROM /{/FROM /d;}\' Dockerfile >> Dockerfile.tmp'
         subprocess.run(command, shell=True, check=True, cwd=path)
 
         # Build the container.

configuration/build_config.yaml

@@ -10,3 +10,4 @@ Layers:
   - ../layers/appdev
   - ../layers/embdgen
   - ../layers/vscode
+  - ../layers/squash

layers/squash/Dockerfile

@@ -0,0 +1,4 @@
+FROM ubuntu:latest as base_container_name 
+
+FROM scratch
+COPY --from=base_container_name / /

layers/squash/README.md

@@ -0,0 +1 @@
+# EBcL SDK: Squash layer