title: docker-compose thinks file is a directory
body: <p>Any ideas?</p>
  <p>This service was starting before but now I get this '/etc/Caddyfile: is a directory' message and the service Exits.</p>
  <pre><code>$ docker-compose -f docker-compose-linux.yml up caddy
  Starting server_applications_1 ... done
  server_workspace_1 is up-to-date
  server_php-fpm_1 is up-to-date
  Starting server_caddy_1        ... done
  Attaching to server_caddy_1
  caddy_1         | http plugins loaded: git
  caddy_1         | 2020/06/22 06:22:18 loading Caddyfile via flag: read /etc/Caddyfile: is a directory
  server_caddy_1 exited with code 1
  </code></pre>
  <p>the caddy service dockerfile:</p>
  <pre><code>FROM zuohuadong/caddy:alpine
  MAINTAINER Huadong Zuo &lt;admin@zuohuadong.cn&gt;
  ARG plugins=&quot;cors&quot;
  WORKDIR /var/www/platform/public
  CMD [&quot;/usr/bin/caddy&quot;, &quot;-conf&quot;, &quot;/etc/Caddyfile&quot;]
  </code></pre>
  <p>the Caddy service container yml:  where CADDY_CUSTOM_CADDYFILE=./caddy/Caddyfile</p>
  <pre>      volumes:
          - ${CADDY_CUSTOM_CADDYFILE}:/etc/Caddyfile
  </pre>
  <p>and the Caddyfile is there in the right directory</p>
  <pre><code>...server/caddy$ ll
  total 16
  drwxrwxr-x  2 ubuntu ubuntu 4096 Jun 22 17:44 ./
  drwxrwxr-x 11 ubuntu ubuntu 4096 Jun 22 15:55 ../
  -rw-r--r--  1 ubuntu ubuntu 1452 Jun 11 10:54 Caddyfile
  -rw-r--r--  1 ubuntu ubuntu  268 Jun 22 18:13 Dockerfile
  </code></pre>
  <p>$ docker-compose -f docker-compose-linux.yml up caddy</p>
  <p>Starting server_applications_1 ... done
  server_workspace_1 is up-to-date
  server_php-fpm_1 is up-to-date
  Starting server_caddy_1        ... done
  Attaching to server_caddy_1
  caddy_1         | http plugins loaded: git
  caddy_1         | 2020/06/22 06:22:18 loading Caddyfile via flag: read /etc/Caddyfile: is a directory
  server_caddy_1 exited with code 1</p>