Validate garm configurator max runner

charms/garm-configurator/charmcraft.yaml

@@ -84,9 +84,9 @@ config:
         Minimum number of idle runners in the scaleset.
     max-runner:
       type: int
-      default: 0
+      default: 1
       description: |
-        Maximum number of runners in the scaleset.
+        Maximum number of runners in the scaleset. Must be greater than 0.
     labels:
       type: string
       description: |

charms/garm-configurator/src/charm_state.py

@@ -250,9 +250,9 @@ def from_charm(cls, charm: ops.CharmBase) -> "ScalesetConfig":
             )
 
         max_runner = int(charm.config.get(SCALESET_MAX_RUNNER_CONFIG_NAME, 0))
-        if max_runner < 0:
+        if max_runner <= 0:
             raise CharmConfigInvalidError(
-                f"{SCALESET_MAX_RUNNER_CONFIG_NAME} must be non-negative"
+                f"{SCALESET_MAX_RUNNER_CONFIG_NAME} must be greater than 0"
             )
         if max_runner < min_idle_runner:
             raise CharmConfigInvalidError(

charms/garm-configurator/tests/unit/test_charm.py

@@ -129,9 +129,14 @@ def test_charm_waiting_with_valid_config_no_relation():
         ),
         pytest.param(
             {"max-runner": -5},
-            "max-runner must be non-negative",
+            "max-runner must be greater than 0",
             id="negative-max-runner",
         ),
+        pytest.param(
+            {"max-runner": 0},
+            "max-runner must be greater than 0",
+            id="zero-max-runner",
+        ),
         pytest.param(
             {"min-idle-runner": 5, "max-runner": 3},
             "max-runner must be greater than or equal to min-idle-runner",

charms/garm-configurator/tox.toml

@@ -37,7 +37,7 @@ commands = [
 
 [env.unit]
 description = "Run unit tests"
-deps = ["pytest", "coverage[toml]", "ops-scenario==8.7.1", "-r requirements.txt"]
+deps = ["pytest", "coverage[toml]", "ops-scenario==8.8.0", "-r requirements.txt"]
 commands = [
   [
     "coverage",

charms/tests/integration/test_garm_configurator.py

@@ -53,6 +53,7 @@ def deploy_garm_configurator_app_fixture(
             "name": "test-scaleset",
             "flavor": "m1.large",
             "os-arch": "amd64",
+            "max-runner": "1",
             "repo": "myorg/myrepo",
         },
     )

docs/changelog.md

@@ -8,6 +8,10 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/).
 
 Each revision is versioned by the date of the revision.
 
+## 2026-07-06
+
+- `garm-configurator`: reject `max-runner=0` during config validation. GARM rejects scale set creation with `max_runners cannot be 0`, so the charm now surfaces the invalid configuration before publishing unusable scale set data to GARM.
+
 ## 2026-07-02
 
 - Fix GARM organization and repository registration: the charm now sets a webhook secret when registering entities. GARM requires a non-empty webhook secret to register an org/repo, so registration previously failed with an opaque server error and scalesets were never created. The charm generates a throwaway secret automatically, so no operator configuration is required.