release: open-source release build logic for unix packages

Updates tailscale/corp#9221

Signed-off-by: David Anderson <danderson@tailscale.com>

release/rpm/rpm.postinst.sh

@@ -0,0 +1,41 @@
+# $1 == 1 for initial installation.
+# $1 == 2 for upgrades.
+
+if [ $1 -eq 1 ] ; then
+    # Normally, the tailscale-relay package would request shutdown of
+    # its service before uninstallation. Unfortunately, the
+    # tailscale-relay package we distributed doesn't have those
+    # scriptlets. We definitely want relaynode to be stopped when
+    # installing tailscaled though, so we blindly try to turn off
+    # relaynode here.
+    #
+    # However, we also want this package installation to look like an
+    # upgrade from relaynode! Therefore, if relaynode is currently
+    # enabled, we want to also enable tailscaled. If relaynode is
+    # currently running, we also want to start tailscaled.
+    #
+    # If there doesn't seem to be an active or enabled relaynode on
+    # the system, we follow the RPM convention for package installs,
+    # which is to not enable or start the service.
+    relaynode_enabled=0
+    relaynode_running=0
+    if systemctl is-enabled tailscale-relay.service >/dev/null 2>&1; then
+        relaynode_enabled=1
+    fi
+    if systemctl is-active tailscale-relay.service >/dev/null 2>&1; then
+        relaynode_running=1
+    fi
+
+    systemctl --no-reload disable tailscale-relay.service >/dev/null 2>&1 || :
+    systemctl stop tailscale-relay.service >/dev/null 2>&1 || :
+
+    if [ $relaynode_enabled -eq 1 ]; then
+        systemctl enable tailscaled.service >/dev/null 2>&1 || :
+    else
+        systemctl preset tailscaled.service >/dev/null 2>&1 || : 
+    fi
+
+    if [ $relaynode_running -eq 1 ]; then
+        systemctl start tailscaled.service >/dev/null 2>&1 || :
+    fi
+fi