emacs/var/elfeed/db/data/eb/ebdd6ff8b65e6ef41268bf7b4eb4dc2d7919fe99

<p>Creating a Docker image isn’t particularly difficult, but I never do
it often enough to remember the incantations required. Yesterday I
needed a Docker image for running CI jobs on <a href="https://circleci.com/">Circle CI</a>.
There are some great pre-built images out there, but I couldn’t find
the combination of Java 17, Leiningen, and Node that I was looking
for. This is a quick guide to how to build your own image with the
tools <em>you</em> need.</p>
<h2 id="great-artists-steal">Great Artists Steal</h2>
<p>First off we want to find a suitable base image to start with. Docker
images are built in layers, so we can start with a solid foundation
pre-written by an expert and simply layer on the additional bits we
need. Circle CI has a great set of <a href="https://circleci.com/docs/2.0/circleci-images/">pre-built Docker
images</a> that take care of the heavy lifting.</p>
<p>Here we’ll use their <code>cimg/openjdk:17.0.1-node</code> image. This is a
variant of their <code>cimg/openjdk:17.0.1</code> image which already includes
Node. Two pieces already done for us!</p>
<p>Create a new <code>Dockerfile</code> and add the following:</p>
<pre><code>FROM cimg/openjdk:17.0.1-node
MAINTAINER Your Name &lt;you@your.domain&gt;
</code></pre><p>To layer on Leiningen, I cribbed the relevant incantations from <a href="https://hub.docker.com/_/clojure">the
official Clojure Docker images</a>. From that
page you can click on any of the <code>Dockerfile</code> links to see how they’re
defined and borrow what you need.</p>
<p>In my case, I simply grabbed these lines and appended them to my
<code>Dockerfile</code>:</p>
<pre><code>### INSTALL LEIN ###
ENV LEIN_VERSION=2.9.8
ENV LEIN_INSTALL=/usr/local/bin/
WORKDIR /tmp
# Download the whole repo as an archive
RUN set -eux; \
sudo apt-get update &amp;&amp; \
sudo apt-get install -y gnupg wget &amp;&amp; \
sudo rm -rf /var/lib/apt/lists/* &amp;&amp; \
mkdir -p $LEIN_INSTALL &amp;&amp; \
wget -q https://raw.githubusercontent.com/technomancy/leiningen/$LEIN_VERSION/bin/lein-pkg &amp;&amp; \
echo "Comparing lein-pkg checksum ..." &amp;&amp; \
sha256sum lein-pkg &amp;&amp; \
echo "9952cba539cc6454c3b7385ebce57577087bf2b9001c3ab5c55d668d0aeff6e9 *lein-pkg" | sha256sum -c - &amp;&amp; \
sudo mv lein-pkg $LEIN_INSTALL/lein &amp;&amp; \
sudo chmod 0755 $LEIN_INSTALL/lein &amp;&amp; \
export GNUPGHOME="$(mktemp -d)" &amp;&amp; \
export FILENAME_EXT=jar &amp;&amp; \
if printf '%s\n%s\n' "2.9.7" "$LEIN_VERSION" | sort -cV; then \
gpg --batch --keyserver hkps://keys.openpgp.org --recv-keys 6A2D483DB59437EBB97D09B1040193357D0606ED; \
else \
gpg --batch --keyserver hkps://keyserver.ubuntu.com --recv-keys 20242BACBBE95ADA22D0AFD7808A33D379C806C3; \
FILENAME_EXT=zip; \
fi &amp;&amp; \
wget -q https://github.com/technomancy/leiningen/releases/download/$LEIN_VERSION/leiningen-$LEIN_VERSION-standalone.$FILENAME_EXT &amp;&amp; \
wget -q https://github.com/technomancy/leiningen/releases/download/$LEIN_VERSION/leiningen-$LEIN_VERSION-standalone.$FILENAME_EXT.asc &amp;&amp; \
echo "Verifying file PGP signature..." &amp;&amp; \
gpg --batch --verify leiningen-$LEIN_VERSION-standalone.$FILENAME_EXT.asc leiningen-$LEIN_VERSION-standalone.$FILENAME_EXT &amp;&amp; \
gpgconf --kill all &amp;&amp; \
rm -rf "$GNUPGHOME" leiningen-$LEIN_VERSION-standalone.$FILENAME_EXT.asc &amp;&amp; \
sudo mkdir -p /usr/share/java &amp;&amp; \
sudo mv leiningen-$LEIN_VERSION-standalone.$FILENAME_EXT /usr/share/java/leiningen-$LEIN_VERSION-standalone.jar &amp;&amp; \
sudo apt-get purge -y --auto-remove gnupg wget
ENV PATH=$PATH:$LEIN_INSTALL
ENV LEIN_ROOT 1
</code></pre><p>I’m very glad I didn’t have to write all of that myself because I
would have been tempted to cut corners on the validation of the
Leiningen package contents and that wouldn’t have been good.</p>
<h2 id="building-the-image">Building the Image</h2>
<p>Now we have everything we need to build the image. Open a shell to
the location where you put the <code>Dockerfile</code> and run the following
command (making appropriate name substitutions for your Docker
organization and desired image name):</p>
<div class="highlight"><pre><code class="language-sh">docker build --tag collbox/clojure-ci .
</code></pre></div><p>Docker will pull the base image, layer on your changes, and create a
new local image.</p>
<p>If you’re ready to share that image with your coworkers or build
server, push it to Docker Hub with:</p>
<div class="highlight"><pre><code class="language-sh">docker push collbox/clojure-ci
</code></pre></div><p>By default the image will be private. If you haven’t added any
private information, you can make the image public and make it easy to
access without adding authentication. Do this by logging into <a href="https://hub.docker.com/">Docker
Hub</a>, clicking the image, “Settings”, and “Make public”.</p>
<h2 id="next-steps">Next Steps</h2>
<p>Now you’re ready to use your new Docker image from a project by simply
using the name we tagged the image with above (<code>collbox/clojure-ci</code>,
in this example).</p>
<p>Finally, why not version control your <code>Dockerfile</code> and add a
<code>Makefile</code> for next time you forget this process and need to update
the image?</p>
<div class="highlight"><pre><code class="language-sh">image<span style="color: #f92672;">=</span>collbox/clojure-ci
build:
docker build --tag <span style="color: #66d9ef;">$(</span>image<span style="color: #66d9ef;">)</span> .
push:
docker push <span style="color: #66d9ef;">$(</span>image<span style="color: #66d9ef;">)</span>
.PHONY: build push
</code></pre></div><p>Now you can rebuild the image with a simple <code>make build</code> or re-push it
with <code>make push</code>.</p>
<p>That’s all there is to it.</p>
<hr />
<p>If you want to see the code above fully
assembled, check out <a href="https://github.com/collbox/clojure-ci-docker">collbox/clojure-ci-docker on
GitHub</a>.</p>