Docker yum install issue - Cannot retrieve metalink for repository: epel/x86_64
<p>While doing <code>yum install</code> from docker file getting the following error message in Centos 7</p>

<p><strong>docker build -f DockerFile .</strong></p>

<pre><code>Sending build context to Docker daemon 1.252 MB
Step 1 : FROM centos:7
 ---&gt; 778a53015523
Step 2 : RUN rpm -iUvh http://dl.fedoraproject.org/pub/epel/7/x86_64/e/epel-release-7-5.noarch.rpm # For python-pip
 ---&gt; Using cache
 ---&gt; 324c446a8ded
Step 3 : RUN rpm --import http://repo.saltstack.com/yum/redhat/7/x86_64/latest/SALTSTACK-GPG-KEY.pub
 ---&gt; Using cache
 ---&gt; bdab0cf0e83d
Step 4 : RUN yum install -y python-pip
 ---&gt; Running in 092314f6bd8f
Loaded plugins: fastestmirror, ovl


 One of the configured repositories failed (Unknown),
 and yum doesn't have enough cached data to continue. At this point the only
 safe thing yum can do is fail. There are a few ways to work "fix" this:

     1. Contact the upstream for the repository and get them to fix the problem.

     2. Reconfigure the baseurl/etc. for the repository, to point to a working
        upstream. This is most often useful if you are using a newer
        distribution release than is supported by the repository (and the
        packages for the previous distribution release still work).

     3. Disable the repository, so yum won't use it by default. Yum will then
        just ignore the repository until you permanently enable it again or use
        --enablerepo for temporary usage:

            yum-config-manager --disable &lt;repoid&gt;

     4. Configure the failing repository to be skipped, if it is unavailable.
        Note that yum will try to contact the repo. when it runs most commands,
        so will have to try and fail each time (and thus. yum will be be much
        slower). If it is a very temporary problem though, this is often a nice
        compromise:

            yum-config-manager --save --setopt=&lt;repoid&gt;.skip_if_unavailable=true

Cannot retrieve metalink for repository: epel/x86_64. Please verify its path and try again
The command '/bin/sh -c yum install -y python-pip' returned a non-zero code: 1
</code></pre>

<p>Our Servers are behind proxy servers. So proxy entries are added in the file 
   <code>/etc/sysconfig/docker</code></p>

<pre><code> HTTP_PROXY=&lt; PROXY_IP &gt;:80/
 HTTPS_PROXY=&lt; PROXY_IP &gt;:80/
</code></pre>

<p>Also added the Env File in 
   <code>docker.service</code></p>

<pre><code>[Service]
    EnvironmentFile=-/etc/sysconfig/docker
</code></pre>

<p>Any help would be greatly appreciated.</p>