fix: avoid namespace edition for k8s users without access rights

In most cases, it makes very little sense to edit the namespace that an
application is running in. Quite often, users are granted access to just one
namespace and don't have the necessary rights to edit the namespace -- and for
good security reasons. In such cases, the k8s namespace object already exists
and there is no need for the user to edit or create it. Here, what we do is
that we create the namespace only if it does not exist. This should solve quite
a few permission issues, notably for Openshift users.

CHANGELOG.md

@@ -4,6 +4,7 @@ Note: Breaking changes between versions are indicated by "💥".
 
 ## Unreleased
 
+- [Improvement] Avoid permission issues in Kubernetes/Openshift for users who do not have the rights to edit their namespace.
 - [Improvement] Better Kubernetes object creation.
 
 ## v11.3.0 (2021-05-18)

tutor/commands/k8s.py

@@ -151,7 +151,7 @@ def run_job(self, service: str, command: str) -> int:
         field_selector = "metadata.name={}".format(job_name)
         while True:
             namespaced_jobs = K8sClients.instance().batch_api.list_namespaced_job(
-                self.config["K8S_NAMESPACE"], field_selector=field_selector
+                k8s_namespace(self.config), field_selector=field_selector
             )
             if not namespaced_jobs.items:
                 continue
@@ -215,15 +215,23 @@ def quickstart(context: click.Context, non_interactive: bool) -> None:
 @click.command(help="Run all configured Open edX services")
 @click.pass_obj
 def start(context: Context) -> None:
-    # Create namespace
-    utils.kubectl(
-        "apply",
-        "--kustomize",
-        tutor_env.pathjoin(context.root),
-        "--wait",
-        "--selector",
-        "app.kubernetes.io/component=namespace",
-    )
+    config = tutor_config.load(context.root)
+    # Create namespace, if necessary
+    # Note that this step should not be run for some users, in particular those
+    # who do not have permission to edit the namespace.
+    try:
+        utils.kubectl("get", "namespaces", k8s_namespace(config))
+        fmt.echo_info("Namespace already exists: skipping creation.")
+    except exceptions.TutorError:
+        fmt.echo_info("Namespace does not exist: now creating it...")
+        utils.kubectl(
+            "apply",
+            "--kustomize",
+            tutor_env.pathjoin(context.root),
+            "--wait",
+            "--selector",
+            "app.kubernetes.io/component=namespace",
+        )
     # Create volumes
     utils.kubectl(
         "apply",
@@ -455,7 +463,7 @@ def kubectl_exec(
 ) -> int:
     selector = "app.kubernetes.io/name={}".format(service)
     pods = K8sClients.instance().core_api.list_namespaced_pod(
-        namespace=config["K8S_NAMESPACE"], label_selector=selector
+        namespace=k8s_namespace(config), label_selector=selector
     )
     if not pods.items:
         raise exceptions.TutorError(