snix/docs/tips-and-tricks.md

Kontemplate tips & tricks

Update Deployments when ConfigMaps change

Kubernetes does not currently have the ability to perform rolling updates of Deployments and other resource types when ConfigMap or Secret objects are updated.

It is possible to make use of annotations and templating functions in Kontemplate to force updates to these resources anyways (assuming that the ConfigMap or Secret contains interpolated variables).

For example:

# A ConfigMap that contains some data structure in JSON format
---
kind: ConfigMap
metadata:
  name: app-config
data:
  configFile: {{ .appConfig | json }}

Now whenever the appConfig variable changes we would like to update the Deployment making use of it, too. We can do this by adding a hash of the configuration to the annotations of the created Pod objects:

---
kind: Deployment
metadata:
  name: app
spec:
  template:
    metadata:
      annotations:
        configHash: {{ .appConfig | json | sha256sum }}
    spec:
      containers:
        - name: app
          # Some details omitted ... 
          volumeMounts:
            - name: config
              mountPath: /etc/app/
      volumes:
        - name: config
          configMap:
            name: app-config

Now if the ConfigMap object appears first in the resource files, kubectl will apply the resources sequentially and the updated annotation will cause a rolling update of all relevant pods.

direnv & pass

Users of pass may have multiple different password stores on their machines. Assuming that kontemplate configuration exists somewhere on the filesystem per project, it is easy to use direnv to switch to the correct PASSWORD_STORE_DIR variable when entering the folder.