openstack-helm/doc/source/devref/upgrades.rst

Upgrades and Reconfiguration

The OpenStack-Helm project assumes all upgrades will be done through Helm. This includes handling several different resource types. First, changes to the Helm chart templates themselves are handled. Second, all of the resources layered on top of the container image, such as ConfigMaps which includes both scripts and configuration files, are updated during an upgrade. Finally, any image references will result in rolling updates of containers, replacing them with the updating image.

As Helm stands today, several issues exist when you update images within charts that might have been used by jobs that already ran to completion or are still in flight. OpenStack-Helm developers will continue to work with the Helm community or develop charts that will support job removal prior to an upgrade, which will recreate services with updated images. An example of where this behavior would be desirable is when an updated db_sync image has updated to point from a Mitaka image to a Newton image. In this case, the operator will likely want a db_sync job, which was already run and completed during site installation, to run again with the updated image to bring the schema inline with the Newton release.

The OpenStack-Helm project also implements annotations across all chart configmaps so that changing resources inside containers, such as configuration files, triggers a Kubernetes rolling update. This means that those resources can be updated without deleting and redeploying the service and can be treated like any other upgrade, such as a container image change.

Note: Rolling update values can conflict with values defined in each service's PodDisruptionBudget. See here for more information.

This is accomplished with the following annotation:

...
annotations:
  configmap-bin-hash: {{ tuple "configmap-bin.yaml" . | include "helm-toolkit.utils.hash" }}
  configmap-etc-hash: {{ tuple "configmap-etc.yaml" . | include "helm-toolkit.utils.hash" }}

The hash function defined in the helm-toolkit chart ensures that any change to any file referenced by configmap-bin.yaml or configmap-etc.yaml results in a new hash, which will then trigger a rolling update.

All chart components (except DaemonSets) are outfitted by default with rolling update strategies:

spec:
  replicas: {{ .Values.replicas }}
  revisionHistoryLimit: {{ .Values.upgrades.revision_history }}
  strategy:
    type: {{ .Values.upgrades.pod_replacement_strategy }}
    {{ if eq .Values.upgrades.pod_replacement_strategy "RollingUpdate" }}
    rollingUpdate:
      maxUnavailable: {{ .Values.upgrades.rolling_update.max_unavailable }}
      maxSurge: {{ .Values.upgrades.rolling_update.max_surge }}
    {{ end }}

In values.yaml in each chart, the same defaults are supplied in every chart, which allows the operator to override at upgrade or deployment time.

upgrades:
  revision_history: 3
  pod_replacement_strategy: RollingUpdate
  rolling_update:
    max_unavailable: 1
    max_surge: 3