hubot-scripts has supported this since
48a3b142 (Added REDIS_URL to
support dokku, 2014-03-01). It still doesn't match Docker's
REDIS_PORT, but it's more generic than the provider-specific
REDISCLOUD_URL.
# Container networking happens automatically
RUN sed -i 's/need net$/use net/' /etc/init.d/*
-CMD cd hubot && REDISCLOUD_URL="${REDIS_PORT}" LOG_REDIS_URL="${REDIS_PORT}" PORT=80 exec bin/hubot --name "${HUBOT_IRC_NICK:-hubot}" -a irc
+CMD cd hubot && REDIS_URL="${REDIS_PORT}" LOG_REDIS_URL="${REDIS_PORT}" PORT=80 exec bin/hubot --name "${HUBOT_IRC_NICK:-hubot}" -a irc
EXPOSE 80
EXPOSE 8000