jinja-init dockerfile

jinja-init is a Docker image that can be used to run an init container in Kubernetes. It uses the Jinja templating system to generate configuration files using config maps, secrets and environment variables.

To learn more about Jinja2 templates have a look at the project documentation.

Example usage

You can either build the image:

$ docker build -t jinja-init:latest .

Or get it from the Docker hub:

$ docker pull objectiflibre/jinja-init

To use the container in Kubernetes:

1. Create a configMap object to store the Jinja template:

   $ cat > template.php.j2 << EOF
   <?php
   \$db_pass = '{{ db_pass }}';
   \$db_host = '{{ db_host }}';
   \$db_user = '{{ db_user }}';
   ?>
   EOF
   $ kubectl create configmap config-template --from-file=template.php.j2

2. Create some secrets (optional). In this example only the db_pass variable is stored as a secret, the other variables will be defined as a container environment variables:

   $ PASSWORD=$(echo -n 's3cr3t' | base64)
   $ cat > secrets.yml << EOF
   apiVersion: v1
   kind: Secret
   metadata:
     name: secrets
   data:
     db_pass: $PASSWORD
   EOF
   $ kubectl apply -f secrets.yml

3. Define your deployment. The generated configuration file needs to be stored on a volume (can be an emptyDir) to share it between the init container and the application container.

   db_host and db_user are defined as environment variables, with the JINJA_VAR_ prefix. This is optional, all the template variables could be stored in the secret.

   In this exemple the application container runs a single command to display the content of the generated file.

   $ cat > deployment.yml << EOF
   apiVersion: apps/v1
   kind: Deployment
   metadata:
     name: test
     labels:
       app: test
   spec:
     replicas: 1
     selector:
       matchLabels:
         app: test
     template:
       metadata:
         labels:
           app: test
       spec:
         initContainers:
         - name: config
           image: objectiflibre/jinja-init
           env:
           # source and destination files
           - name: JINJA_SRC_FILE
             value: /config_src/template.php.j2
           - name: JINJA_DEST_FILE
             value: /config/config.php
           - name: JINJA_VAR_db_host
             value: /secrets
           # let's be verbose
           - name: VERBOSE
             value: "1"
           # extra variables used in the template
           - name: JINJA_VAR_db_host
             value: "127.0.0.1"
           - name: JINJA_VAR_db_user
             value: app_user
           volumeMounts:
           # configMap mount point
           - name: config-template
             mountPath: /config_src
           # target directory mount point; the final config file will be created here
           - name: config
             mountPath: /config
           # /secrets is the default mount point used by jinja-init
           - name: secrets
             mountPath: /secrets
         containers:
         - name: busybox
           image: busybox
           command: ["cat", "/config/config.php"]
           volumeMounts:
           - name: config
             mountPath: /config
         volumes:
         - name: config-template
           configMap:
             name: config-template
         - name: config
           emptyDir:
         - name: secrets
           secret:
             secretName: secrets
   EOF
   $ kubectl apply -f deployment.yml
   $ kubectl logs deployment/test
   <?php
   $db_pass = 'password';
   $db_host = '127.0.0.1';
   $db_user = 'app_user';
   ?>

Variables

The container supports the following variables:

JINJA_SRC_FILE

Path of the source template.

Default: /config_src/template.j2

JINJA_DEST_FILE

Path of the destination file (file generated from the template).

Default: /config/settings.py

JINJA_SECRETS_DIR

Directory containing the secrets. The name of each file in this folder become the name of a jinja variable, and the content of the file is the value.

Default: /secrets

VERBOSE

If defined the script will output extra information about what it is doing.

JINJA_VAR_*

Extra jinja variables. The JINJA_VAR_ prefix is removed from the variable name. The variable name in case sensitive.

Contributing

We welcome new ideas and contributions. You can use issues and pull requests to help us improve this tool.