instruction for 1.5.2-tectonic.2 clusters to switch coreupdate channel

instruction.md

As we are changing the channel model in CoreUpdate Server since 1.5.3-tectonic.1 release, users on clusters with older version (1.5.2-tectonic.2) need to manually modify their channel operator’s config to switch to the new CoreUpdate channel.

This can be done by replacing channel: alpha with channel: tectonic-1.5 in the channel operator’s config.

For example:

kubectl replace -f -<<EOF
apiVersion: coreos.com/v1
appID: 6bc7b986-4654-4a0f-94b3-84ce6feb1db4
automaticUpdate: false
channel: tectonic-1.5
kind: ChannelOperatorConfig
metadata:
  name: default
  namespace: tectonic-system
server: https://tectonic.update.core-os.net
triggerUpdate: false
triggerUpdateCheck: false
updateCheckInterval: 2700
EOF

After that, users will subscribe the tectonic-1.5 channel. To check for an update manually, click the "Check for Updates" button in the console UI.

When there is an available update, the button will turn green and become "Start Update". Click the button will trigger the upgrade.