diff --git a/templates/acng.conf.j2 b/templates/acng.conf.j2
index 5e5c2ff..d024e33 100644
--- a/templates/acng.conf.j2
+++ b/templates/acng.conf.j2
@@ -23,4 +23,10 @@ PassThroughPattern: .*
 Proxy: {{ proxy_env_url }}
 {% endif %}
 VfilePatternEx: ^/\?release=[0-9]+&arch=
+# NOTE(mhayden): Caching the CentOS mirror list causes yum to throw
+# 503 errors intermittently since the remote file is dynamic. Also,
+# yum has issues with retrieving the mariadb.org repodata bz2 and
+# that causes more intermittent 503 errors. This DontCache line
+# tells apt-cacher-ng to allow requests for these to pass through
+# without being cached.
 DontCache: (mirrorlist.centos.org)|(mariadb.org.*.bz2$)