Rolling Upgrade Deployment, StatefulSet, DaemonSet

Introduction to Rolling Upgrades

ConfigMaps and Secrets are Kubernetes resources designed to decouple configuration details from application code, fostering a clear separation between the configuration data and the application logic. This separation yields several compelling advantages, making the practice of mounting ConfigMaps and Secrets a crucial component of Kubernetes deployments.

1. Configuration Flexibility: Applications often require various configuration settings to function optimally across different environments. By mounting ConfigMaps, developers can modify configuration parameters without altering the application code. This not only streamlines the development process but also allows for on-the-fly adjustments, facilitating smooth transitions between development, testing, and production environments.
2. Enhanced Security: Secrets, such as sensitive authentication tokens, passwords, and API keys, contain critical information that must be safeguarded. Instead of hardcoding these sensitive details directly into the application code, they can be stored as Secrets and mounted into pods only when necessary. This mitigates the risk of inadvertent exposure and helps maintain a higher level of security.

React to ConfigMap/Secret changes

Sveltos has the capability to monitor changes within ConfigMap and Secret resources and facilitate rolling upgrades for Deployments, StatefulSets, and DaemonSets. This functionality can be activated by setting the reloader field to true in the ClusterProfile, as demonstrated in the below YAML configuration.

apiVersion: config.projectsveltos.io/v1alpha1
kind: ClusterProfile
metadata:
  name: nginx
spec:
  clusterSelector: env=fv
  reloader: true
  policyRefs:
  - name: nginx-data
    namespace: default
    kind: ConfigMap
  - name: nginx
    namespace: default
    kind: ConfigMap

The nginx ConfigMap contains a Deployment mounting a ConfigMap¹.

The above ClusterProfile is responsible for deploying both a ConfigMap instance and a Deployment instance, with the latter mounting a ConfigMap.

& sveltosctl show addons          
+-----------------------------+---------------------------------+-----------+---------------------+---------+-------------------------------+------------------------------+
|           CLUSTER           |          RESOURCE TYPE          | NAMESPACE |        NAME         | VERSION |             TIME              |       CLUSTER PROFILES       |
+-----------------------------+---------------------------------+-----------+---------------------+---------+-------------------------------+------------------------------+
| default/clusterapi-workload | :ConfigMap                      | nginx     | nginx-config        | N/A     | 2023-08-09 05:00:45 -0700 PDT | nginx                        |
| default/clusterapi-workload | apps:Deployment                 | nginx     | nginx-deployment    | N/A     | 2023-08-09 05:00:45 -0700 PDT | nginx                        |
+-----------------------------+---------------------------------+-----------+---------------------+---------+-------------------------------+------------------------------+

Whenever the ConfigMap that is mounted by a Deployment undergoes modifications, Sveltos will automatically initiate a rolling upgrade process for the Deployment.

By setting the reloader field to true, you enable automated rolling upgrades that ensure the latest configurations are consistently applied down the applications. This significantly simplifies the maintenance and enhancement of your Kubernetes cluster, promoting stability and efficient resource utilization.

1. Deployments: When a ConfigMap or Secret mounted by a Deployment is modified, Sveltos promptly detects the change and initiates a rolling upgrade for that Deployment. This ensures that any changes in configuration or secrets are promptly and securely propagated to the running instances of the application.
2. StatefulSets: Similar to Deployments, StatefulSets can take advantage of Sveltos' monitoring capabilities. Modifications to the ConfigMap or Secret mounted by a StatefulSet will trigger rolling updates for the StatefulSet instances. This allows for controlled and consistent updates to stateful applications while maintaining data integrity.
3. DaemonSets: Sveltos extends its monitoring to DaemonSets. If a ConfigMap or a Secret used by a DaemonSet is modified, Sveltos takes the initiative to perform a rolling upgrade across all the nodes where the DaemonSet is deployed. This way, any changes made to the resources are efficiently propagated throughout the cluster.

---

1. nginx-data ConfigMap

   apiVersion: v1
   data:
     configmap.yaml: "# nginx-config.yaml\napiVersion: v1\nkind: ConfigMap\nmetadata:\n
       \ name: nginx-config\n  namespace: nginx\ndata:\n  nginx.conf: |\n    server {\n
       \     listen 80;\n      server_name example.com;\n      \n      location / {\n
       \       root /usr/share/nginx/html;\n        index index.html;\n      }\n    }\n"
   kind: ConfigMap
   metadata:
     name: nginx-data
     namespace: default
   

   and the nginx ConfigMap

   apiVersion: v1
   data:
     deployment.yaml: |
       # nginx-deployment.yaml
       apiVersion: apps/v1
       kind: Deployment
       metadata:
         name: nginx-deployment
         namespace: nginx
       spec:
         replicas: 1
         selector:
           matchLabels:
             app: nginx
         template:
           metadata:
             labels:
               app: nginx
           spec:
             containers:
               - name: nginx
                 image: nginx:latest
                 ports:
                   - containerPort: 80
                 volumeMounts:
                   - name: nginx-config-volume
                     mountPath: /etc/nginx/conf.d/default.conf
                     subPath: nginx.conf
             volumes:
               - name: nginx-config-volume
                 configMap:
                   name: nginx-config
   kind: ConfigMap
   metadata:
     name: nginx
     namespace: default
   

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