Support k8s 1.19 and higher (#734)

* Test on lowest and highest k8s version and 1.19

Signed-off-by: Pavol Loffay <p.loffay@gmail.com>

* Add comment

Signed-off-by: Pavol Loffay <p.loffay@gmail.com>

* Fix

Signed-off-by: Pavol Loffay <p.loffay@gmail.com>

* Fix

Signed-off-by: Pavol Loffay <p.loffay@gmail.com>

* Add more comments

Signed-off-by: Pavol Loffay <p.loffay@gmail.com>

.github/workflows/e2e.yaml

@@ -12,9 +12,11 @@ jobs:
     runs-on: ubuntu-20.04
     strategy:
       matrix:
+       # The e2e tests are run on the lowest and highest supported k8s version.
+       # All Kubernetes version in between expose the same APIs, hence the operator
+       # should be compatible with them.
        kube-version:
-       - "1.21"
-       - "1.22"
+       - "1.19"
        - "1.23"
 
     steps:

.github/workflows/scorecard.yaml

@@ -14,9 +14,7 @@ jobs:
       matrix:
         kube-version:
           - "1.19"
-          - "1.20"
-          - "1.21"
-          - "1.22"
+          - "1.23"
 
     steps:
 

README.md

@@ -228,11 +228,7 @@ When a custom `Spec.Image` is used with an `OpenTelemetryCollector` resource, th
 
 ### OpenTelemetry Operator vs. Kubernetes vs. Cert Manager
 
-We strive to be compatible with the widest range of Kubernetes versions as possible, but some changes to Kubernetes itself require us to break compatibility with older Kubernetes versions, be it because of code incompatibilities, or in the name of maintainability.
-
-Our promise is that we'll follow what's common practice in the Kubernetes world and support N-2 versions, based on the release date of the OpenTelemetry Operator.
-
-For instance, when we released v0.27.0, the latest Kubernetes version was v1.21.1. As such, the minimum version of Kubernetes we support for OpenTelemetry Operator v0.27.0 is v1.19 and we tested it with up to 1.21.
+We strive to be compatible with the widest range of Kubernetes versions as possible, but some changes to Kubernetes itself require us to break compatibility with older Kubernetes versions, be it because of code incompatibilities, or in the name of maintainability. Every released operator will support a specific range of Kubernetes versions, to be determined at the latest during the release.
 
 We use `cert-manager` for some features of this operator and the third column shows the versions of the `cert-manager` that are known to work with this operator's versions.