docker: use single parameterized Dockerfile for all images

Signed-off-by: Anatoli Babenia <anatoli@rainforce.org>

docker/beta.Dockerfile → docker/Dockerfile

@@ -1,5 +1,9 @@
+ARG RISK=edge
+
 FROM ubuntu:xenial as builder
 
+RUN echo "Building snapcraft:$RISK"
+
 # Grab dependencies
 RUN apt-get update
 RUN apt-get dist-upgrade --yes
@@ -13,8 +17,8 @@ RUN curl -L $(curl -H 'X-Ubuntu-Series: 16' 'https://api.snapcraft.io/api/v1/sna
 RUN mkdir -p /snap/core
 RUN unsquashfs -d /snap/core/current core.snap
 
-# Grab the snapcraft snap from the beta channel and unpack it in the proper place
-RUN curl -L $(curl -H 'X-Ubuntu-Series: 16' 'https://api.snapcraft.io/api/v1/snaps/details/snapcraft?channel=beta' | jq '.download_url' -r) --output snapcraft.snap
+# Grab the snapcraft snap from the $RISK channel and unpack it in the proper place
+RUN curl -L $(curl -H 'X-Ubuntu-Series: 16' 'https://api.snapcraft.io/api/v1/snaps/details/snapcraft?channel='$RISK | jq '.download_url' -r) --output snapcraft.snap
 RUN mkdir -p /snap/snapcraft
 RUN unsquashfs -d /snap/snapcraft/current snapcraft.snap
 

docker/README.md

@@ -9,19 +9,19 @@ like `--dns=8.8.8.8` added to the command.
 
 ## Creating containers
 
-There are four separate Dockerfiles here, each one corresponding to their
-respective risk level:
+The Dockerfile here can build images for these risk levels:
 
-- **edge.Dockerfile**: Using the snap from edge
-- **beta.Dockerfile**: Using the snap from beta
-- **candidate.Dockerfile**: Using the snap from candidate
-- **stable.Dockerfile**: Using the snap from stable
+- **edge**: Using the snap from edge
+- **beta**: Using the snap from beta
+- **candidate**: Using the snap from candidate
+- **stable**: Using the snap from stable
 
-Build the docker image with the following (note that `--network host` is not
-strictly needed if a proper docker bridge is setup):
+By default, the `edge` image will be built. Pass `--build-arg RISK=<risk>` to
+choose needed risk level for target container:
 
-    docker build --no-cache -f <risk>.Dockerfile --label snapcore/snapcraft --tag snapcore/snapcraft:<risk> --network host .
+    export RISK=beta
+    docker build --no-cache --tag snapcore/snapcraft:$RISK --build-arg RISK=$RISK .
 
 You can push that image with:
 
-    docker push snapcore/snapcraft:<risk>
+    docker push snapcore/snapcraft:$RISK