Update on Istio addon to specify the version to install

[10alejospain]

Update on Istio addon to specify the version to install

Problem addresed

This update targets #152 where an update on the Istio version is requested and a way to select the version wanted.

Solution

• By adding the flag --istio-version when enabling the addon you can choose a version between the available ones.
• The command checks for the official Istio releases and if not available it aborts the operation.
• If the flag is not set it will enable the latest version available.

Other changes

• Updated the disable script.
• Updated unit test.

Command structure

microk8s enable istio --istio-version 19.0.0

Also verify you have:

• Read the contributions page.
• Submitted the CLA form, if you are a first time contributor.