Replacing your current base image with the Docker Alpine Linux image usually requires updating the package names to the corresponding ones in the Alpine Linux package index. We use the
apk command to manage packages. It works similar to
An example installing the
nginx package would be
apk add --update-cache nginx. The
--update-cache flag fetches the current package index before adding the package. We don't ship the image with a package index (since that can go stale fairly quickly).
Here is a full example
Dockerfile that installs the Python runtime and some build dependencies:
FROM gliderlabs/alpine:3.3 RUN apk add --update-cache \ python \ python-dev \ py-pip \ build-base \ && pip install virtualenv \ && rm -rf /var/cache/apk/* WORKDIR /app ONBUILD COPY . /app ONBUILD RUN virtualenv /env && /env/bin/pip install -r /app/requirements.txt EXPOSE 8080 CMD ["/env/bin/python", "main.py"]
As of Alpine Linux 3.3 there exists a new
--no-cache option for
apk. It allows users to install packages with an index that is updated and used on-the-fly and not cached locally:
FROM gliderlabs/alpine:3.3 RUN apk --no-cache add nginx EXPOSE 80 CMD ["nginx", "-g", "daemon off;"]
This avoids the need to use
--update-cache and remove
/var/cache/apk/* when done installing packages.
gliderlabs variant of this image contains a small unofficial wrapper script that assists in the cleanup of the package index after installing packages. However, this functionality is now available in the upstream
apk utility as of Alpine version 3.2 (using
apk --no-cache). This script may be removed from the
gliderlabs/alpine images in the future.
apk add feature for cleanup is the concept of virtual packages using the
-t switch. Packages added under this virtual name can then be removed as one group. An example use of this would be removing a group of build dependencies all at once:
FROM gliderlabs/alpine:3.3 WORKDIR /myapp COPY . /myapp RUN apk --update-cache add python py-pip openssl ca-certificates RUN apk --update-cache add --virtual build-dependencies python-dev build-base wget \ && pip install -r requirements.txt \ && python setup.py install \ && apk del build-dependencies CMD ["myapp", "start"]
Check out the Alpine Linux package management documentation for more information and usage of