Scoped Variables

Introduction

In Devtron, many configuration values such as a database name, memory limit, or service endpoint may need to be used in multiple places. Instead of entering the same value repeatedly, you can store it in a scoped variable.

A scoped variable (key-value pair) allows you to define a value once and reuse it. The value of the variable will depend on the scopes mentioned below:

For example, you can create a variable named db_host to store the database host URL and set its value to https://dev.company.com/mydb for development environment, and for production environment you can set its value to https://prod.company.com/mydb, at the time of deployment, Devtron will automatically choose the correct value based on the environment.

The table below illustrates how Devtron uses scoped variables defined for different scopes

Precedence of Scoped Variables

If the same variable is defined at more than one scope, Devtron resolves the value based on the following precedence order:

1. Environment + App: This is the most specific scope, and it will take precedence over all other scopes. For example, the value of DB_Name variable for the app1 application in the dev environment would be dev-app1-db, even though there is a global DB_Name variable set to central-db. If a variable value for this scope is not defined, the App scope will be checked.

2. Application: This is the next most specific scope, and it will take precedence over the Environment, Cluster, and Global scopes. For example, the value of DB_Name variable for the app1 application would be app1-db, even though the value of DB_Name exists in lower scopes. If a variable value for this scope is not defined, the Environment scope will be checked.

3. Environment: This is the next most specific scope, and it will take precedence over the Cluster and Global scopes. For example, the value of DB_Name variable in the prod environment would be prod-db, even though the value of DB_Name exists in lower scopes. If a variable value for this scope is not defined, the Cluster scope will be checked.

4. Cluster: This is the next most specific scope, and it will take precedence over the Global scope. For example, the value of DB_Name variable in the GKE cluster would be gke-db, even though there is a global DB_Name variable set to central-db. If a variable value for this scope is not defined, the Global scope will be checked.

5. Global: This is the least specific scope, and it will only be used if no variable values are found in other higher scopes. The value of DB_Name variable would be central-db.

Advantages of using scoped variables

• Reduces repeatability: Configuration management team can centrally maintain the static data.

• Simplifies bulk edits: All the places that use a scoped variable, get updated when you change the value of the variable without requiring manual edits. If the scoped variable is being used in Deployment Template, ConfigMap, Secret, or Job the actual value will be resolved and propagated upon next trigger.

• Keeps data secure: You can mark a variable as sensitive, so its value is hidden in the UI, reducing the risk of misuse or leakage. Refer How to Define a Scoped Variable to learn more.

How to Define a Scoped Variable

In Devtron, you can define scoped variables by using a YAML template. It will contain a schema for defining the scoped variables.

Depending on your use case, you can do either one of the following:

Download the Template

1. From the left sidebar, go to Global Configurations → Scoped Variables

2. Click Download template.

   
3. Open the downloaded template using any code editor (say VS Code).

Enter the Values

The YAML file contains key-value pairs that follow the below schema:

The spec.values array further contains the following elements:

Here's a truncated template containing the specification of two variables for your understanding:

apiVersion: devtron.ai/v1beta1
kind: Variable
spec:

# First example of a variable
  - name: DB_URL
    shortDescription: My application's customers are stored
    notes: The DB is a MySQL DB running version 7.0. The DB contains confidential
      information.
    isSensitive: true
    values:
      - category: Global
        value: mysql.example.com

# Second example of a variable
  - name: DB_Name
    shortDescription: My database name to recognize the DB
    notes: NA
    isSensitive: false
    values:
      - category: Global
        value: Devtron
      - category: ApplicationEnv
        value: app1-p
        selectors:
          attributeSelectors:
            ApplicationName: MyFirstApplication
            EnvName: prod

Upload the Template

1. Once you save the YAML file, go back to the screen where you downloaded the template.

2. Click Upload file to add, to upload your saved YAML file.

   
3. The content of the file will be uploaded for you to review and edit. Click Review Changes.

   
4. You may check the changes between the last saved file and the current one before clicking Save.

   
5. Click the Variable List tab to view the variables. Check the How to Use a Scoped Variable section to know more.

   

Defining YAML values in scoped variables

In Devtron, Scoped variables usually store simple values like strings or numbers, for example, if you want to connect multiple applications to the same SonarQube server, you can define a variable for its endpoint URL once instead of entering it everywhere.

SONAR_ENDPOINT: https://sonarqube.yourcompany.com

But, in some cases, you may need to define more detailed configuration in a scoped variable, such as autoscaling configuration or resource configuration. You can achieve this by defining a YAML snippet as the value of a scoped variable.

Defining YAML snippets as the value of a scoped variable will help you to reuse YAML configuration across multiple applications or environments. Scoped variables with YAML snippets can be changed based on the context (category) such as Global, Cluster, Environment, Application, Environment+Application.

Here's a truncated template containing the specification of one scoped variable with a YAML snippet as its value defined for different contexts for your understanding:

apiVersion: devtron.ai/v1beta1
kind: Variable
spec:
  - notes: Resource Configuration
    shortDescription: Scoped variable with YAML snippet
    isSensitive: false
    name: resources # Defining name for the variable.
    values:
      - category: Application
        value:  # Insert the YAML configuration block with proper indentation
          limits:
            cpu: 100m
            memory: 100Mi
          requests:
            cpu: 100m
            memory: 100Mi
        selectors:
          attributeSelectors:
            ApplicationName: banking-preprod
      - category: Env # Defining the variable for an environment.
        value: 
            limits:
              cpu: 75m
              memory: 75Mi
            requests:
              cpu: 50m
              memory: 50Mi
        selectors:
          attributeSelectors:
            EnvName: devtron-demo # Specifying the environment
      - category: Env # Defining variable's values for another environment
        value: 
          limits:
            cpu: 200m
            memory: 200Mi
          requests:
            cpu: 100m
            memory: 100Mi
        selectors:
          attributeSelectors:
            EnvName: banking # Specifying another environment name.
      - category: Global # Defining Variable's Values for global context.
        value:
          limits:
            cpu: 50m
            memory: 50Mi
          requests:
            cpu: 50m
            memory: 50Mi

How to Edit an Existing Scoped Variable

Only a super-admin can edit existing scoped variables.

Option 1: Directly edit using the UI

Option 2: Reupload the updated YAML file

Option 3: Edit through 'Environments' tab

The Environments tab allows you to view and edit scoped variable values for individual environments.

1. Go to the Environments tab; you will see a list of all environments and how many scoped variables are defined for each of them.

1. Click the preferred environment name to view or edit.

2. You can edit the variables using the GUI or YAML mode.

How to Use a Scoped Variable

Once a variable is defined, it can be used by your authorized users on Devtron. A scoped variable widget would appear only on the screens that support its usage.

Currently, the widget is shown only on the following screens in App Configuration:

• Workflow Editor → Edit build pipeline → Pre-build stage (tab)

• Workflow Editor → Edit build pipeline → Post-build stage (tab)

• Workflow Editor → Edit deployment pipeline → Post-Deployment stage (tab)

• Workflow Editor → Edit deployment pipeline → Post-Deployment stage (tab)

• Deployment Template

• ConfigMaps

• Secrets

To use a scoped variable, click on the floating widget; a list of variables will be visible.

Use the copy button to copy a relevant variable of your choice.

It would appear in the following format upon pasting it within an input field: @{{variable-name}}.

In case you are using a scoped variable in deployment template, you need to encapsulate it in double quotes i.e., "@{{variable-name}}"

Note: Ignore the red underline while using a scoped variable in the deployment template.

List of Predefined Variables

There are some system variables that exist by default in Devtron that you can readily use if needed:

• DEVTRON_NAMESPACE: Provides name of the namespace

• DEVTRON_CLUSTER_NAME: Provides name of the cluster configured on Devtron

• DEVTRON_ENV_NAME: Provides name of the environment

• DEVTRON_IMAGE_TAG: Provides image tag associated with the container image

• DEVTRON_IMAGE: Provides full image path of the container image, e.g., gcr.io/k8s-minikube/kicbase:v0.0.39

• DEVTRON_APP_NAME: Provides name of the application on Devtron