= Usage

== Packages
Replacing your current base image with the Docker Alpine Linux image usually requires updating the package names to the corresponding ones in the https://pkgs.alpinelinux.org[Alpine Linux package index].
We use the `apk` command to manage packages.
It works similarly to `apt` and `yum`.

For example, installing the `nginx` package would be done by running `apk add --no-cache nginx`.
The `--no-cache` argument prevents `apk` from caching the package index - something that would normally take up precious space, as well as go stale quickly.

=== Example
This is an example of a complete Dockerfile for `nginx`:
[source, dockerfile]
----
FROM alpine

RUN apk --no-cache add nginx

EXPOSE 80
CMD ["nginx", "-g", "daemon off;"]
----

=== Virtual Packages
Another great `apk` feature is the concept of user-defined virtual packages.
Packages added under a virtual package name can later be removed as one group.
An example use-case would be removing all build dependencies at once, as in this example:
[source, dockerfile]
----
FROM alpine

WORKDIR /myapp
COPY . /myapp

RUN apk add --no-cache python py-pip openssl ca-certificates
RUN apk add --no-cache --virtual build-dependencies python-dev build-base wget \
  && pip install -r requirements.txt \
  && python setup.py install \
  && apk del build-dependencies

CMD ["myapp", "start"]
----

// COMBAK: update docs link
=== Further Details
For further details on `apk` and how it's used, you can look at https://docs.alpinelinux.org/user-handbook/0.1a/Working/apk.html[Alpine's User Documentation] for it.