Your First Flag

This guide walks you through creating a feature flag and delivering it to a workload.

1. Create a FeatureFlag

apiVersion: vexil.io/v1alpha1
kind: FeatureFlag
metadata:
  name: dark-mode
  namespace: default
spec:
  description: "Enable dark mode for the frontend"
  type: boolean
  defaultValue: "false"
  delivery:
    envVar:
      name: FEATURE_DARK_MODE
      selector:
        matchLabels:
          app: frontend

Apply it:

kubectl apply -f - <<EOF
apiVersion: vexil.io/v1alpha1
kind: FeatureFlag
metadata:
  name: dark-mode
  namespace: default
spec:
  description: "Enable dark mode for the frontend"
  type: boolean
  defaultValue: "false"
  delivery:
    envVar:
      name: FEATURE_DARK_MODE
      selector:
        matchLabels:
          app: frontend
EOF

2. Check the flag status

kubectl get featureflags
# or use the short name:
kubectl get ff

Output:

NAME        TYPE      DEFAULT   PHASE    TARGETED   AGE
dark-mode   boolean   false     Active   0          5s

3. Deploy a workload that receives the flag

The flag targets pods with label app: frontend. Create a simple deployment:

kubectl create deployment frontend --image=nginx
kubectl label deployment frontend app=frontend

The operator will inject FEATURE_DARK_MODE=false into the deployment’s containers.

Verify:

kubectl get deployment frontend -o jsonpath='{.spec.template.spec.containers[0].env}' | jq

[
  {
    "name": "FEATURE_DARK_MODE",
    "value": "false"
  }
]

4. Toggle the flag

Update the value:

kubectl patch featureflag dark-mode \
  -p '{"spec":{"defaultValue":"true"}}' --type=merge

Or toggle via the API:

curl -X POST http://localhost:8090/api/v1/flags/default/dark-mode/toggle \
  -H "Authorization: Bearer $TOKEN"

The operator will update the environment variable in the deployment, triggering a rolling update.

5. View in the dashboard

Open the Vexil web dashboard to see your flag, its status, targeted workloads, and delivery configuration.

What’s Next?

• Delivery Methods — Learn about environment variables, ConfigMaps, and the sidecar
• Targeting Rules — Deliver different values based on workload attributes
• Rollout Strategies — Gradually roll out flag changes
• Client SDKs — Read flags from your application code