Allow usage of mirror Jenkins Update-Center for downloading plugins
Sometimes (like today ... and many other times unfortunately) the main
Jenkins update center is down and you cannot build a Jenkins Docker image.
It is much better than to include the full base URL as JENKINS_UC_DOWNLOAD
so that the ENV variable can be overridden to point to an up-and-running site.
Example:
ENV JENKINS_UC_DOWNLOAD http://mirrors.clinkerhq.com/jenkins
diff --git a/Dockerfile b/Dockerfile
index 64071db..d5b2da5 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -30,6 +30,7 @@
&& echo "$JENKINS_SHA /usr/share/jenkins/jenkins.war" | sha1sum -c -
ENV JENKINS_UC https://updates.jenkins-ci.org
+ENV JENKINS_UC_DOWNLOAD $JENKINS_UC/download
RUN chown -R jenkins "$JENKINS_HOME" /usr/share/jenkins/ref
# for main web interface: