refactor: Add MtailDeployer

- This splits the existing deploy_mtail() routine into methods for the
  install, configure, and activate stages.

cmdeploy/src/cmdeploy/__init__.py

@@ -747,59 +747,71 @@ def deploy_turn_server(config):
     )
 
 
-def deploy_mtail(config):
-    # Uninstall mtail package, we are going to install a static binary.
-    apt.packages(name="Uninstall mtail", packages=["mtail"], present=False)
+class MtailDeployer(Deployer):
+    def __init__(self, *, mtail_address, **kwargs):
+        super().__init__(**kwargs)
+        self.mtail_address = mtail_address
 
-    (url, sha256sum) = {
-        "x86_64": (
-            "https://github.com/google/mtail/releases/download/v3.0.8/mtail_3.0.8_linux_amd64.tar.gz",
-            "123c2ee5f48c3eff12ebccee38befd2233d715da736000ccde49e3d5607724e4",
-        ),
-        "aarch64": (
-            "https://github.com/google/mtail/releases/download/v3.0.8/mtail_3.0.8_linux_arm64.tar.gz",
-            "aa04811c0929b6754408676de520e050c45dddeb3401881888a092c9aea89cae",
-        ),
-    }[host.get_fact(facts.server.Arch)]
+    @staticmethod
+    def install_impl():
+        # Uninstall mtail package, we are going to install a static binary.
+        apt.packages(name="Uninstall mtail", packages=["mtail"], present=False)
 
-    server.shell(
-        name="Download mtail",
-        commands=[
-            f"(echo '{sha256sum} /usr/local/bin/mtail' | sha256sum -c) || (curl -L {url} | gunzip | tar -x -f - mtail -O >/usr/local/bin/mtail.new && mv /usr/local/bin/mtail.new /usr/local/bin/mtail)",
-            "chmod 755 /usr/local/bin/mtail",
-        ],
-    )
+        (url, sha256sum) = {
+            "x86_64": (
+                "https://github.com/google/mtail/releases/download/v3.0.8/mtail_3.0.8_linux_amd64.tar.gz",
+                "123c2ee5f48c3eff12ebccee38befd2233d715da736000ccde49e3d5607724e4",
+            ),
+            "aarch64": (
+                "https://github.com/google/mtail/releases/download/v3.0.8/mtail_3.0.8_linux_arm64.tar.gz",
+                "aa04811c0929b6754408676de520e050c45dddeb3401881888a092c9aea89cae",
+            ),
+        }[host.get_fact(facts.server.Arch)]
 
-    # Using our own systemd unit instead of `/usr/lib/systemd/system/mtail.service`.
-    # This allows to read from journalctl instead of log files.
-    files.template(
-        src=importlib.resources.files(__package__).joinpath("mtail/mtail.service.j2"),
-        dest="/etc/systemd/system/mtail.service",
-        user="root",
-        group="root",
-        mode="644",
-        address=config.mtail_address or "127.0.0.1",
-        port=3903,
-    )
+        server.shell(
+            name="Download mtail",
+            commands=[
+                f"(echo '{sha256sum} /usr/local/bin/mtail' | sha256sum -c) || (curl -L {url} | gunzip | tar -x -f - mtail -O >/usr/local/bin/mtail.new && mv /usr/local/bin/mtail.new /usr/local/bin/mtail)",
+                "chmod 755 /usr/local/bin/mtail",
+            ],
+        )
 
-    mtail_conf = files.put(
-        name="Mtail configuration",
-        src=importlib.resources.files(__package__).joinpath(
-            "mtail/delivered_mail.mtail"
-        ),
-        dest="/etc/mtail/delivered_mail.mtail",
-        user="root",
-        group="root",
-        mode="644",
-    )
+    def configure_impl(self):
+        # Using our own systemd unit instead of `/usr/lib/systemd/system/mtail.service`.
+        # This allows to read from journalctl instead of log files.
+        files.template(
+            src=importlib.resources.files(__package__).joinpath(
+                "mtail/mtail.service.j2"
+            ),
+            dest="/etc/systemd/system/mtail.service",
+            user="root",
+            group="root",
+            mode="644",
+            address=self.mtail_address or "127.0.0.1",
+            port=3903,
+        )
 
-    systemd.service(
-        name="Start and enable mtail",
-        service="mtail.service",
-        running=bool(config.mtail_address),
-        enabled=bool(config.mtail_address),
-        restarted=mtail_conf.changed,
-    )
+        mtail_conf = files.put(
+            name="Mtail configuration",
+            src=importlib.resources.files(__package__).joinpath(
+                "mtail/delivered_mail.mtail"
+            ),
+            dest="/etc/mtail/delivered_mail.mtail",
+            user="root",
+            group="root",
+            mode="644",
+        )
+        self.need_restart = mtail_conf.changed
+
+    def activate_impl(self):
+        systemd.service(
+            name="Start and enable mtail",
+            service="mtail.service",
+            running=bool(self.mtail_address),
+            enabled=bool(self.mtail_address),
+            restarted=self.need_restart,
+        )
+        self.need_restart = False
 
 
 class IrohDeployer(Deployer):
@@ -931,6 +943,7 @@ def deploy_chatmail(config_path: Path, disable_mail: bool) -> None:
 
     nginx_deployer = NginxDeployer(config=config)
     journald_deployer = JournaldDeployer()
+    mtail_deployer = MtailDeployer(mtail_address=config.mtail_address)
 
     all_deployers = [
         unbound_deployer,
@@ -941,6 +954,7 @@ def deploy_chatmail(config_path: Path, disable_mail: bool) -> None:
         postfix_deployer,
         nginx_deployer,
         journald_deployer,
+        mtail_deployer,
     ]
 
     #
@@ -1116,4 +1130,6 @@ def deploy_chatmail(config_path: Path, disable_mail: bool) -> None:
         mode="700",
     )
 
-    deploy_mtail(config)
+    mtail_deployer.install()
+    mtail_deployer.configure()
+    mtail_deployer.activate()