Example Dynamic Nginx Deployment based on Annotations

Scenario Description

In a fast-changing and often complex Kubernetes environment, it is important for Platform teams and engineers to automate application deployments using unique identifiers. For instance, actions or deployments can be triggered only when a Kubernetes resource has a specific annotation.

This example demonstrates how namespace annotations can be used as key identifiers. By using these annotations, Sveltos can automatically deploy different versions of the Nginx server to different namespaces based on the annotations set.

Namespace EventSource

Example - EventSource Definition

cat > eventsource.yaml <<EOF
---
apiVersion: lib.projectsveltos.io/v1beta1
kind: EventSource
metadata:
  name: find-all-namespaces
spec:
  collectResources: true
  resourceSelectors:
  - group: ""
    version: "v1"
    kind: "Namespace"

The EventSource described above will trigger the following EventTrigger action for each namespace in the Kubernetes cluster.

EventTrigger Defintion

Example - EventTrigger Definition

---
apiVersion: lib.projectsveltos.io/v1beta1
kind: EventTrigger
metadata:
  name: deploy-nginx
spec:
  sourceClusterSelector:
    matchLabels:
      env: fv
  eventSourceName: find-all-namespaces
  oneForEvent: true
  policyRefs:
  - name: deploy-nginx
    namespace: default
    kind: ConfigMap

Example - ConfigMap deploy-nginx

---
apiVersion: v1
kind: ConfigMap
metadata:
  name: deploy-nginx
  namespace: default
  annotations:
    projectsveltos.io/instantiate: ok # this annotation is what tells Sveltos to instantiate this ConfigMap
data:
  networkpolicy.yaml: |
    apiVersion: apps/v1
    kind: Deployment
    metadata:
      name: nginx-deployment
      namespace: {{ .Resource.metadata.name }}
      labels:
        app: nginx
    spec:
      replicas: 1
      selector:
        matchLabels:
          app: nginx
      template:
        metadata:
          labels:
            app: nginx
        spec:
          containers:
          - name: nginx
            {{- if (index .Resource.metadata `annotations`) -}}
            {{- if (index .Resource.metadata.annotations `nginx`) }}
            image: nginx:{{ .Resource.metadata.annotations.nginx }}
            {{- else }} # nginx key does NOT exist within annotations
            image: nginx:1.14.2
            {{- end }}
            {{- else }} # annotations not present
            image: nginx:1.14.2
            {{- end }}
            ports:
            - containerPort: 80

When the EventTrigger resource is activated, Sveltos is instructed to deploy the ConfigMap named deploy-nginx only to managed clusters labeled with env:fv.

The ConfigMap is expressed as a Sveltos Template, which allows simple conditions to determine which Nginx version should be deployed based on the namespace annotation.

{{- if (index .Resource.metadata `annotations`) -}}
{{- if (index .Resource.metadata.annotations `nginx`) }}
image: nginx:{{ .Resource.metadata.annotations.nginx }}
{{- else }} # nginx key does NOT exist within annotations
image: nginx:1.14.2
{{- end }}
{{- else }} # annotations not present
image: nginx:1.14.2
{{- end }}

If the annotation nginx is present in a namespace, Nginx with the specified version (image: nginx:) will be installed. If the nginx annotation is missing or no annotations are set, Nginx version 1.14.2 will be installed by default.

Next Steps

To explore more about the powerful features of Sveltos Templates, have a look here.