diff --git a/.travis.yml b/.travis.yml
index 51cd08d..25c5275 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -9,6 +9,7 @@ before_install:
     - docker build  -f 06-ci/test/Dockerfile      -t wordpress06   06-ci
     - docker build  -f 10-role/test/Dockerfile    -t wordpress10   10-role
     - docker build  -f 11-galaxy/test/Dockerfile  -t wordpress11   11-galaxy
+    - docker build  -f 20-cluster/test/Dockerfile -t wordpress20   20-cluster
 
 script:
     - docker run -d --name wordpress06   wordpress06
@@ -26,8 +27,16 @@ script:
     - IP=$(docker inspect --format '{{ .NetworkSettings.IPAddress }}' wordpress11) ; echo http://$IP:80/ > url
     - cat url  |  xargs -t -n 1 curl -v --retry 5 --retry-max-time 120 -o result-wordpress11
 
+    - docker run -d --name db20  db20
+    - sleep 60
+    - docker run -d --name wordpress20  --link db20:MYSQL_ADDRESS  wordpress20
+    - sleep 300
+    - IP=$(docker inspect --format '{{ .NetworkSettings.IPAddress }}' wordpress20) ; echo http://$IP:80/ > url
+    - cat url  |  xargs -t -n 1 curl -v -o result-wordpress20
+
 
     - echo "==> Validating the test results..."
     - grep '<title>ANSIBLE_TEST' result-wordpress06
     - grep '<title>ANSIBLE_TEST' result-wordpress10
     - grep '<title>ANSIBLE_TEST' result-wordpress11
+    - grep '<title>ANSIBLE_TEST' result-wordpress20
diff --git a/20-cluster/README.md b/20-cluster/README.md
index d1ef77d..ebdb5fc 100644
--- a/20-cluster/README.md
+++ b/20-cluster/README.md
@@ -44,6 +44,4 @@ Separated by...
 
 - Avoid the "all hosts" `%` setting in the MySQL `GRANT PRIVILEGES` statement.
 
-- Use the [container links](https://docs.docker.com/engine/userguide/networking/default_network/dockerlinks/) feature of Docker to simplify the testing Dockerfiles.
-
 - Use [Docker Compose](https://github.com/docker/compose) to simplify the testing job.
diff --git a/20-cluster/Vagrantfile b/20-cluster/Vagrantfile
index 3fce2a2..5da35f1 100644
--- a/20-cluster/Vagrantfile
+++ b/20-cluster/Vagrantfile
@@ -29,4 +29,28 @@ Vagrant.configure("2") do |config|
         end
     end
 
+
+    # docker: for auto build & testing (e.g., Travis CI)
+    config.vm.define "docker" do |node|
+        node.vm.box = "williamyeh/ubuntu-trusty64-docker"
+
+        node.vm.provision "shell", inline: <<-SHELL
+            cd /vagrant
+
+            docker build  -f test/Dockerfile-db         -t db         .
+            docker build  -f test/Dockerfile-wordpress  -t wordpress  .
+
+            docker run -d --name db  db
+            sleep 60
+            docker run -d --name wordpress  --link db:MYSQL_ADDRESS  wordpress
+            sleep 300
+
+            IP=$(docker inspect --format '{{ .NetworkSettings.IPAddress }}' wordpress) ; echo http://$IP:80/ > url
+            cat url  |  xargs -t -n 1 curl -v -o result-wordpress
+
+            echo "==> Validating the test results..."
+            grep '<title>ANSIBLE_TEST' result-wordpress
+        SHELL
+    end
+
 end
diff --git a/20-cluster/test/Dockerfile-wordpress b/20-cluster/test/Dockerfile-wordpress
new file mode 100644
index 0000000..7ad5cb4
--- /dev/null
+++ b/20-cluster/test/Dockerfile-wordpress
@@ -0,0 +1,49 @@
+# Dockerfile for building image that contains software stack provisioned by Ansible.
+#
+# USAGE:
+#   $ docker build -t wordpress .
+#   $ docker run -d  wordpress
+#
+# Version  1.1
+#
+
+
+# pull base image
+FROM williamyeh/ansible:ubuntu14.04-onbuild
+
+MAINTAINER William Yeh <william.pjyeh@gmail.com>
+
+
+#
+# build phase
+#
+
+
+# fix policy-rc.d for Docker
+# @see http://www.monblocnotes.com/node/2057
+# @see http://askubuntu.com/a/365912
+RUN sed -i -e 's/exit\s\s*101/exit 0/' /usr/sbin/policy-rc.d
+
+
+# ==> Specify requirements filename;  default = "requirements.yml"
+#ENV REQUIREMENTS  requirements.yml
+
+ENV PLAYBOOK wordpress.yml
+RUN ansible-playbook-wrapper  \
+      --extra-vars "modify_hostname=false mysql_address=MYSQL_ADDRESS"
+
+EXPOSE 80
+
+
+#
+# start the service via CMD
+#
+
+CMD \
+    service php7.0-fpm start                      && \
+    service nginx start                           && \
+    IP=`head -n 1 /etc/hosts | sed 's/\t.*//'`    && \
+    PLAYBOOK=init-wordpress.yml      \
+       ansible-playbook-wrapper -vvv \
+         --extra-vars `echo hostname=$IP`         && \
+    tail -f /dev/null
\ No newline at end of file
diff --git a/circle.yml b/circle.yml
index 5cd9fd6..597c6cb 100644
--- a/circle.yml
+++ b/circle.yml
@@ -10,6 +10,7 @@ dependencies:
     - docker build  -f 06-ci/test/Dockerfile      -t wordpress06   06-ci
     - docker build  -f 10-role/test/Dockerfile    -t wordpress10   10-role
     - docker build  -f 11-galaxy/test/Dockerfile  -t wordpress11   11-galaxy
+    - docker build  -f 20-cluster/test/Dockerfile -t wordpress20   20-cluster
 
 
 test:
@@ -29,8 +30,16 @@ test:
     - IP=$(docker inspect --format '{{ .NetworkSettings.IPAddress }}' wordpress11) ; echo http://$IP:80/ > url
     - cat url  |  xargs -t -n 1 curl -v --retry 5 --retry-max-time 120 -o result-wordpress11
 
+    - docker run -d --name db20  db20
+    - sleep 60
+    - docker run -d --name wordpress20  --link db20:MYSQL_ADDRESS  wordpress20
+    - sleep 300
+    - IP=$(docker inspect --format '{{ .NetworkSettings.IPAddress }}' wordpress20) ; echo http://$IP:80/ > url
+    - cat url  |  xargs -t -n 1 curl -v -o result-wordpress20
+
 
     - echo "==> Validating the test results..."
     - grep '<title>ANSIBLE_TEST' result-wordpress06
     - grep '<title>ANSIBLE_TEST' result-wordpress10
     - grep '<title>ANSIBLE_TEST' result-wordpress11
+    - grep '<title>ANSIBLE_TEST' result-wordpress20