how about this way

Dockerfile

@@ -27,6 +27,11 @@ RUN apt-get update && \
     apt-get clean && \
     rm -rf /var/lib/apt/lists/*
 
+RUN echo '' >> /etc/dnsmasq.conf
+# See https://github.com/nicolasff/docker-cassandra/issues/8
+RUN echo 'user=root' >> /etc/dnsmasq.conf
+
+
 WORKDIR /usr/src/app
 
 COPY . .
@@ -45,8 +50,10 @@ RUN chown -R appuser:appuser .
 RUN chown appuser:appuser /config/*
 RUN chmod 0664 /config/*    
 
+RUN echo ''%${GROUP_ID}' ALL=NOPASSWD:/usr/sbin/service dnsmasq *' >> /etc/sudoers
+
 USER appuser
 
 ENV PATH="/usr/src/app/.venv/bin:$PATH"
 
-CMD ["/bin/sh", "-c", "/usr/sbin/dnsmasq && python3 ./app.py -c /config"]
+CMD ["/bin/sh", "-c", "sudo service dnsmasq start && python3 ./app.py -c /config"]