Pin Docker image nginx:alpine

nginx:alpine
->
nginx:alpine@sha256:082f8c10bd47b6acc8ef15ae61ae45dd8fde0e9f389a8b5cb23c37408642bf5d

 [atomist:generated]
 [atomist-skill:atomist/docker-base-image-policy]

Signed-off-by: Atomist Bot <bot@atomist.com>

Dockerfile

@@ -1,11 +1,11 @@
 # Install the base requirements for the app.
 # This stage is to support development.
-FROM python:alpine AS base
+FROM python:alpine@sha256:c9d3c11e89887c82efeb4f4fee8771a406cf42f41aebbd23148906d5fe3c1426 AS base
 WORKDIR /app
 COPY requirements.txt .
 RUN pip install -r requirements.txt
 
-FROM node:12-alpine AS app-base
+FROM node:12-alpine@sha256:d4b15b3d48f42059a15bd659be60afe21762aae9d6cbea6f124440895c27db68 AS app-base
 WORKDIR /app
 COPY app/package.json app/yarn.lock ./
 COPY app/spec ./spec
@@ -36,6 +36,6 @@ RUN mkdocs build
 
 # Extract the static content from the build
 # and use a nginx image to serve the content
-FROM nginx:alpine
+FROM nginx:alpine@sha256:082f8c10bd47b6acc8ef15ae61ae45dd8fde0e9f389a8b5cb23c37408642bf5d
 COPY --from=app-zip-creator /app.zip /usr/share/nginx/html/assets/app.zip
 COPY --from=build /app/site /usr/share/nginx/html