Compatibility Versions

2 minute read

With each new version of Istio, there may be some intentional behavioral changes. These can be to improve security, fix incorrect behavior, or otherwise improve Istio for users. Generally, these types of changes impact only edge cases.

While beneficial on the long term, each behavioral change introduces risk during upgrades. Historically, when upgrading users should read the release notes for any behavioral changes and determine if they are impacted; this can be tedious and error prone.

Compatibility versions give users an additional option, allowing release versions to be decoupled from behavioral changes. For instance, you can install Istio 1.25, but configure it to behave like 1.24.

Using compatibility versions

To use a compatibility version, simply set the compatibilityVersion field.

$ istioctl install --set values.compatibilityVersion=1.24

$ helm install ... --set compatibilityVersion=1.24

When should I use compatibility versions?

Compatibility versions are recommended to be used only when an incompatibility is found, rather than as the default. Each compatibility version will only persist for a few releases, so eventually you will need to migrate to the new behavior. Currently, each compatibility version is intended to remain for at least two versions, though this is subject to change.

To help detect if a compatibility version should be used, istioctl x precheck can be used with the --from-version flag. For instance, if you are upgrading from version 1.24:

$ istioctl x precheck --from-version 1.24
Warning [IST0168] (DestinationRule default/tls) The configuration "ENABLE_AUTO_SNI" changed in release 1.20: previously, no SNI would be set; now it will be automatically set. Or, install with `--set compatibilityVersion=1.20` to retain the old default.
Error: Issues found when checking the cluster. Istio may not be safe to install or upgrade.
See https://istio.io/v1.21/docs/reference/config/analysis for more information about causes and resolutions.