kustomize/examples/wordpress

Demo: WordPress

In this tutorial, you will learn - how to use kustomize to declare a variable reference and substitute it in container's command.

In the WordPress example, we want

• to connect WordPress with a MySQL database
• access the service name of MySQL database from WordPress container

First make a place to work:

DEMO_HOME=$(mktemp -d)
MYSQL_HOME=$DEMO_HOME/mysql
mkdir -p $MYSQL_HOME
WORDPRESS_HOME=$DEMO_HOME/wordpress
mkdir -p $WORDPRESS_HOME

Download resources

Download the resources and kustomization.yaml for WordPress.

CONTENT="https://raw.githubusercontent.com\
/kubernetes-sigs/kustomize\
/master/examples/wordpress/wordpress"

curl -s -o "$WORDPRESS_HOME/#1.yaml" \
  "$CONTENT/{deployment,service,kustomization}.yaml"

Download the resources and kustomization.yaml for MySQL.

CONTENT="https://raw.githubusercontent.com\
/kubernetes-sigs/kustomize\
/master/examples/wordpress/mysql"

curl -s -o "$MYSQL_HOME/#1.yaml" \
  "$CONTENT/{deployment,service,secret,kustomization}.yaml"

Create kustomization.yaml

We create a new kustomization, which has two bases: mysql and wordpress.

cat <<EOF >$DEMO_HOME/kustomization.yaml
bases:
  - wordpress
  - mysql
namePrefix: demo-
EOF

Download patch for WordPress

In the new kustomization, we apply a patch for wordpress deployment. The patch does two things

• Add an initial container to show the mysql service name
• Add environment variable for mysql database so that wordpress can connect to it

CONTENT="https://raw.githubusercontent.com\
/kubernetes-sigs/kustomize\
/master/examples/patch.yaml"

curl -s -o "$DEMO_HOME/#1.yaml" \
  "$CONTENT/{patch}.yaml"

The patch has following content

apiVersion: apps/v1beta2
kind: Deployment
metadata:
  name: wordpress
spec:
  template:
    spec:
      initContainers:
      - name: init-command
        image: debian
        command:
        - "echo $(WORDPRESS_SERVICE)"
        - "echo $(MYSQL_SERVICE)"
      containers:
      - name: wordpress
        env:
        - name: WORDPRESS_DB_HOST
          value: mysql
        - name: WORDPRESS_DB_PASSWORD
          valueFrom:
            secretKeyRef:
              name: mysql-pass
              key: password

In the init container's command, there are two variables as $(WORDPRESS_SERVICE) and $(MYSQL_SERVICE), which are for the service names of wordpress and mysql. If we define those variables in kustomization.yaml, they will be substituted in kustomize build to the correct names.

Add Variable Reference

Let us define the variables needed in the init container's command.

cat <<EOF >>$DEMO_HOME/kustomization.yaml
vars:
  - name: WORDPRESS_SERVICE
    objref:
      kind: Service
      name: wordpress
      apiVersion: v1
    fieldref:
      fieldpath: metadata.name
  - name: MYSQL_SERVICE
    objref:
      kind: Service
      name: mysql
      apiVersion: v1
EOF

WORDPRESS_SERVICE is from the field metadata.name of Service wordpress. If we don't specify fieldref, the default is metadata.name. So MYSQL_SERVICE is from the field metadata.name of Service mysql.

Substitution

We can see the substitution by kustomize build

kustomize build $DEMO_HOME

We will see the init Container's command as

(truncated)
...
     initContainers:
     - command:
       - echo demo-wordpress
       - echo demo-mysql
       image: debian
       name: init-command