apt packages from config

config.yaml

@@ -7,3 +7,8 @@ options:
     description: |
       Comma-separated list of labels to be assigned to the agent in Jenkins. If not set it will
       default to the agents hardware identifier, e.g.: 'x86_64'
+  apt-packages:
+    type: string
+    default: ""
+    description: |
+      Comma-separated list of apt packages to install on the machine.

src/charm.py

@@ -59,6 +59,13 @@ def _on_install(self, _: ops.InstallEvent) -> None:
 
     def _on_config_changed(self, _: ops.ConfigChangedEvent) -> None:
         """Handle config changed event. Update the agent's label in the relation's databag."""
+        try:
+            self.jenkins_agent_service.install_apt_packages(self.state.apt_packages)
+        except service.PackageInstallError as exc:
+            logger.error("Error installing apt packages %s", exc)
+            self.model.unit.status = ops.BlockedStatus("Error installing apt packages: %s")
+            return
+
         if agent_relation := self.model.get_relation(AGENT_RELATION):
             relation_data = self.state.agent_meta.as_dict()
             agent_relation.data[self.unit].update(relation_data)

src/charm_state.py

@@ -17,6 +17,8 @@
 # agent relation name
 AGENT_RELATION = "agent"
 
+APT_PACKAGES_CONFIG = "apt-packages"
+
 logger = logging.getLogger()
 
 
@@ -115,6 +117,21 @@ def _get_credentials_from_agent_relation(
     return Credentials(address=address, secret=secret)
 
 
+def _get_packages_to_install(charm: ops.CharmBase) -> typing.Tuple[str, ...]:
+    """Get list of apt packages to install from charm configuration.
+
+    Args:
+        charm: The charm instance.
+
+    Returns:
+        The list of apt packages to install.
+    """
+    packages = charm.config.get(APT_PACKAGES_CONFIG, "")
+    if not packages:
+        return ()
+    return tuple(package.strip() for package in packages.split(","))
+
+
 @dataclass
 class State:
     """The Jenkins agent state.
@@ -123,12 +140,14 @@ class State:
         agent_meta: The Jenkins agent metadata to register on Jenkins server.
         agent_relation_credentials: The full set of credentials from the agent relation. None if
             partial data is set or the credentials do not belong to current agent.
+        apt_packages: The list of apt packages to install on the unit.
         unit_data: Data about the current unit.
         jenkins_agent_service_name: The Jenkins agent workload container name.
     """
 
     agent_meta: AgentMeta
     agent_relation_credentials: typing.Optional[Credentials]
+    apt_packages: typing.Tuple[str, ...]
     unit_data: UnitData
     jenkins_agent_service_name: str = "jenkins-agent"
 
@@ -176,5 +195,6 @@ def from_charm(cls, charm: ops.CharmBase) -> "State":
         return cls(
             agent_meta=agent_meta,
             agent_relation_credentials=agent_relation_credentials,
+            apt_packages=_get_packages_to_install(charm),
             unit_data=unit_data,
         )

src/service.py

@@ -8,6 +8,7 @@
 import pwd
 import time
 from pathlib import Path
+from typing import Iterable
 
 from charms.operator_libs_linux.v0 import apt
 from charms.operator_libs_linux.v1 import systemd
@@ -123,6 +124,24 @@ def install(self) -> None:
         except (apt.PackageError, apt.PackageNotFoundError, apt.GPGKeyError) as exc:
             raise PackageInstallError("Error installing the agent package") from exc
 
+    @classmethod
+    def install_apt_packages(cls, packages: Iterable[str]) -> None:
+        """Install apt packages.
+
+        Args:
+            packages: The apt packages to install.
+
+        Raises:
+            PackageInstallError: If there was an error installing the package.
+        """
+        to_install = list(packages)
+        if not to_install:
+            return
+        try:
+            apt.add_package(to_install, update_cache=True)
+        except apt.Error as exc:
+            raise PackageInstallError from exc
+
     def restart(self) -> None:
         """Start the agent service.
 

tests/integration/test_agent.py

@@ -10,6 +10,9 @@
 import jenkinsapi.jenkins
 from juju.application import Application
 from juju.model import Model
+from juju.unit import Unit
+
+from charm_state import APT_PACKAGES_CONFIG
 
 from .conftest import NUM_AGENT_UNITS, assert_job_success
 
@@ -63,3 +66,21 @@ async def test_agent_relation(
     assert len(nodes.values()) == NUM_AGENT_UNITS + 1
 
     assert_job_success(jenkins_client, jenkins_agent_application.name, "machine")
+
+
+async def test_agent_packages(
+    model: Model,
+    jenkins_agent_application: Application,
+):
+    """
+    arrange: given a jenkins agent application.
+    act: when the apt-packages configuration is set.
+    assert: the defined packages are installed.
+    """
+    await jenkins_agent_application.set_config({APT_PACKAGES_CONFIG: "bzr, iputils-ping"})
+    await model.wait_for_idle()
+
+    unit: Unit = jenkins_agent_application.units[0]
+
+    assert "/usr/bin/bzr\n" == await unit.ssh("which bzr")
+    assert "/usr/bin/ping\n" == await unit.ssh("which ping")

tests/unit/test_charm.py

@@ -5,16 +5,21 @@
 
 """Test for charm hooks."""
 
+# Need access to protected functions for testing
+# pylint:disable=protected-access
+
 from unittest.mock import MagicMock, PropertyMock
 
 import ops
 import ops.testing
 import pytest
+from charms.operator_libs_linux.v0 import apt
 from charms.operator_libs_linux.v1 import systemd
 
 import charm_state
 import service
 from charm import JenkinsAgentCharm
+from charm_state import APT_PACKAGES_CONFIG
 
 
 def test___init___invalid_state(harness: ops.testing.Harness, monkeypatch: pytest.MonkeyPatch):
@@ -53,6 +58,26 @@ def test__on_upgrade_charm(harness: ops.testing.Harness, monkeypatch: pytest.Mon
     assert charm.unit.status.name == ops.BlockedStatus.name
 
 
+def test__on_config_changed_apt_install_fail(
+    harness: ops.testing.Harness, monkeypatch: pytest.MonkeyPatch
+):
+    """
+    arrange: given a charm with patched relation.
+    act: when _on_config_changed is called.
+    assert: The charm correctly updates the relation databag.
+    """
+    harness.update_config({APT_PACKAGES_CONFIG: "hello,world"})
+    harness.begin()
+    get_relation_mock = MagicMock()
+    monkeypatch.setattr(apt, "add_package", MagicMock(side_effect=apt.PackageNotFoundError))
+    monkeypatch.setattr(ops.Model, "get_relation", get_relation_mock)
+
+    charm: JenkinsAgentCharm = harness.charm
+    charm._on_config_changed(MagicMock())
+
+    assert charm.unit.status.name == ops.BlockedStatus.name
+
+
 def test__on_config_changed(harness: ops.testing.Harness, monkeypatch: pytest.MonkeyPatch):
     """
     arrange: given a charm with patched relation.

tests/unit/test_service.py

@@ -6,6 +6,7 @@
 """Test for service interaction."""
 
 import os
+import typing
 from pathlib import Path
 from unittest.mock import MagicMock
 
@@ -17,6 +18,7 @@
 import service
 from charm import JenkinsAgentCharm
 from charm_state import AGENT_RELATION
+from service import JenkinsAgentService, PackageInstallError
 
 
 @pytest.mark.parametrize(
@@ -72,6 +74,39 @@ def test_on_install(harness: ops.testing.Harness, monkeypatch: pytest.MonkeyPatc
     assert harness.charm.unit.status.name == ops.BlockedStatus.name
 
 
+def test_on_install_packages_fail(monkeypatch: pytest.MonkeyPatch):
+    """
+    arrange: Given a monkeypatched apt lib that raises an error.
+    act: when install_apt_packages is called.
+    assert: PackageInstallError is raised.
+    """
+    monkeypatch.setattr(apt, "add_package", MagicMock(side_effect=apt.PackageNotFoundError))
+
+    with pytest.raises(PackageInstallError):
+        JenkinsAgentService.install_apt_packages(["hello", "world"])
+
+
+@pytest.mark.parametrize(
+    "packages",
+    [
+        pytest.param(tuple(), id="No packages"),
+        pytest.param(("hello", "world"), id="Has packages"),
+    ],
+)
+def test_on_install_packages(monkeypatch: pytest.MonkeyPatch, packages: typing.Tuple[str, ...]):
+    """
+    arrange: Given a monkeypatched apt lib and list of packages to install.
+    act: when install_apt_packages is called.
+    assert: package install call is made.
+    """
+    monkeypatch.setattr(apt, "add_package", (apt_mock := MagicMock()))
+
+    JenkinsAgentService.install_apt_packages(packages)
+
+    if packages:
+        apt_mock.assert_called_once()
+
+
 def test_restart_service(
     harness: ops.testing.Harness,
     monkeypatch: pytest.MonkeyPatch,

tests/unit/test_state.py

@@ -5,7 +5,11 @@
 
 """Test for charm state."""
 
+# Need access to protected functions for testing
+# pylint:disable=protected-access
+
 import os
+import typing
 from unittest.mock import MagicMock
 
 import ops
@@ -14,6 +18,7 @@
 
 import charm_state
 from charm import JenkinsAgentCharm
+from charm_state import APT_PACKAGES_CONFIG
 
 
 def test_from_charm_invalid_metadata(
@@ -30,3 +35,25 @@ def test_from_charm_invalid_metadata(
 
     with pytest.raises(charm_state.InvalidStateError, match="Invalid executor state."):
         charm_state.State.from_charm(charm=charm)
+
+
+@pytest.mark.parametrize(
+    "packages, expected",
+    [
+        pytest.param("", tuple(), id="empty"),
+        pytest.param("git,bzr", ("git", "bzr"), id="has packages"),
+    ],
+)
+def test__get_packages_to_install(
+    harness: ops.testing.Harness, packages: str, expected: typing.Tuple[str, ...]
+):
+    """
+    arrange: given charm apt-packages config.
+    act: when _get_packages_to_install is called.
+    assert: packages are correctly parsed.
+    """
+    harness.begin()
+    harness.update_config({APT_PACKAGES_CONFIG: packages})
+    charm: JenkinsAgentCharm = harness.charm
+
+    assert charm_state._get_packages_to_install(charm=charm) == expected