Openshift templates are Openshift’s answer to Kubernetes helm charts. In this way, an openshift template contains a list of objects. In consequence, applying an openshift template substitutes its placeholders. Also, it contains a parameter list. Openshift template are a built-in feature of Openshift. But what are differences to helm?
How does Openshift Template work?
Openshift Template
apiVersion: v1 kind: Template metadata: name: redis-template name: REDIS_PASSWORD labels: redis: master objects: - apiVersion: v1 kind: Pod metadata: name: redis-master spec: containers: - env: - name: REDIS_PASSWORD value: ${REDIS_PASSWORD} image: dockerfile/redis name: master ports: - containerPort: 6379 protocol: TCP parameters: - description: Password used for Redis authentication from: '[A-Z0-9]{8}' name: REDIS_PASSWORD generate: expressionOpenshift templates are pretty simple. The header introduces the template “> “> (line 1+). The objects section (line 8+) defines a list of cluster objects. Objects may contain placeholder in curly brackets (see line 17). Section of parameters (line 23+) defines parameters to substitute such placeholders. In this example the template requires a parameter REDIS_PASSWORD. The parameters section supplies it.
applying on openshift template
oc process -f template.yaml --param REDIS_PASSWORD=secretoc process -f template.yaml --param REDIS_PASSWORD=secret | oc create -f -oc process -f template.yaml --param REDIS_PASSWORD=secret | ec applay -f -Once openshift template is defined it must be applied to the cluster. The process command (1) reads the template and substitutes parameters and writes results to console. Piping output to “oc create” (3) lets cluster create the new objects. Once created, objects are updated by “oc apply” (5) command.
Openshift Templates versus Helm Charts?
Are Openshift Templates better than Helm charts? There is no easy answer. Notably, Openshift templates are a built-in feature. In contrast, helm requires tiller service installed. Tiller service creates cluster objects. Because of this, Tiller services require cluster-admin permission on Kube-system service account. But for security reasons, most production systems does not grant this permission. Read here for more details.
Conclusion
Templates offer a generic mechanism to deploy applications to different environments. The process of defining a template substitutes environment specific values. Text files may store substitutions. Such text files may be applied to process command.
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