Change base image from CentOS 7 to alpine linux

Dockerfile

@@ -1,14 +1,13 @@
 #Dockerfile for a Postfix email relay service
-FROM centos:7
+FROM alpine
 MAINTAINER Juan Luis Baptiste juan.baptiste@gmail.com
 
-RUN yum install -y epel-release && yum update -y && \
-    yum install -y cyrus-sasl cyrus-sasl-plain cyrus-sasl-md5 mailx \
+RUN apk update && \
+    apk add bash gawk cyrus-sasl cyrus-sasl-plain cyrus-sasl-crammd5 mailx \
     perl supervisor postfix rsyslog \
-    && rm -rf /var/cache/yum/* \
-    && yum clean all
-RUN sed -i -e "s/^nodaemon=false/nodaemon=true/" /etc/supervisord.conf
-RUN sed -i -e 's/inet_interfaces = localhost/inet_interfaces = all/g' /etc/postfix/main.cf
+    rm -rf /var/cache/apk/* && \
+    mkdir -p /var/log/supervisor/ /var/run/supervisor/ && \
+    sed -i -e 's/inet_interfaces = localhost/inet_interfaces = all/g' /etc/postfix/main.cf
 
 COPY etc/ /etc/
 COPY run.sh /