Start dovecot before postfix and add target for certificates

It seemed weird to me that preStart on postfix was used to generate
files not needed directly by postfix and for the self-signed
certificate which is also needed by dovecot. nginx.service was also
used as a proxy for when ACME certificate generation was done.

So I have created mailserver-certificates.target for when certificates
are available for other services. For self-signed that means that a
new oneshot service called mailserver-selfsigned-certificate has been
run. And for ACME this means that the target
acme-selfsigned-certificates has been reached (which is when acme has
created the self-signed certificates used before the actual
certificates provided by LetsEncrypt are created). This setup has the
added bonus that if you want to run a service to provide your own
certificates you can set that to run before
mailserver-certificates.target.

DH Parameters are only needed by dovecot so generation of that file has
been moved to the dovecot2 preStart.

And lastly the only remaining reason to for dovecot to start before
postfix was that the auth and lmtp sockets where located in a directory
created by postfix. But since they could just as well be located in
/run/dovecot2 as long as postfix has access to them I have moved them
there.

mail-server/dovecot.nix

@@ -84,7 +84,7 @@ in
         ''}
 
         service lmtp {
-          unix_listener /var/lib/postfix/queue/private/dovecot-lmtp {
+          unix_listener dovecot-lmtp {
             group = ${postfixCfg.group}
             mode = 0600
             user = ${postfixCfg.user}
@@ -106,7 +106,7 @@ in
         }
 
         service auth {
-          unix_listener /var/lib/postfix/queue/private/auth {
+          unix_listener auth {
             mode = 0660
             user = ${postfixCfg.user}
             group = ${postfixCfg.group}

mail-server/postfix.nix

@@ -121,11 +121,11 @@ in
         virtual_mailbox_domains = ${vhosts_file}
         virtual_mailbox_maps = hash:/var/lib/postfix/conf/valias
         virtual_alias_maps = hash:/var/lib/postfix/conf/valias
-        virtual_transport = lmtp:unix:private/dovecot-lmtp
+        virtual_transport = lmtp:unix:/run/dovecot2/dovecot-lmtp
 
         # sasl with dovecot
         smtpd_sasl_type = dovecot
-        smtpd_sasl_path = private/auth
+        smtpd_sasl_path = /run/dovecot2/auth
         smtpd_sasl_auth_enable = yes
         smtpd_relay_restrictions = permit_mynetworks, permit_sasl_authenticated, reject_unauth_destination
 
@@ -158,7 +158,7 @@ in
         smtpd_tls_security_level = "encrypt";
         smtpd_sasl_auth_enable = "yes";
         smtpd_sasl_type = "dovecot";
-        smtpd_sasl_path = "private/auth";
+        smtpd_sasl_path = "/run/dovecot2/auth";
         smtpd_sasl_security_options = "noanonymous";
         smtpd_sasl_local_domain = "$myhostname";
         smtpd_client_restrictions = "permit_sasl_authenticated,reject";

mail-server/systemd.nix

@@ -19,37 +19,6 @@
 let
   cfg = config.mailserver;
 
-  create_certificate = if cfg.certificateScheme == 2 then
-        ''
-          # Create certificates if they do not exist yet
-          dir="${cfg.certificateDirectory}"
-          fqdn="${cfg.fqdn}"
-          case $fqdn in /*) fqdn=$(cat "$fqdn");; esac
-          key="''${dir}/key-${cfg.fqdn}.pem";
-          cert="''${dir}/cert-${cfg.fqdn}.pem";
-
-          if [ ! -f "''${key}" ] || [ ! -f "''${cert}" ]
-          then
-              mkdir -p "${cfg.certificateDirectory}"
-              (umask 077; "${pkgs.openssl}/bin/openssl" genrsa -out "''${key}" 2048) &&
-                  "${pkgs.openssl}/bin/openssl" req -new -key "''${key}" -x509 -subj "/CN=''${fqdn}" \
-                          -days 3650 -out "''${cert}"
-          fi
-        ''
-        else "";
-
-  createDhParameterFile =
-    ''
-      # Create a dh parameter file
-      if [ ! -s "${cfg.certificateDirectory}/dh.pem" ]
-      then
-          mkdir -p "${cfg.certificateDirectory}"
-          ${pkgs.openssl}/bin/openssl \
-                dhparam ${builtins.toString cfg.dhParamBitLength} \
-                > "${cfg.certificateDirectory}/dh.pem"
-      fi
-    '';
-
   createDomainDkimCert = dom:
     let
       dkim_key = "${cfg.dkimKeyDirectory}/${dom}.${cfg.dkimSelector}.key";
@@ -76,32 +45,85 @@ let
 
           chown -R rmilter:rmilter "${cfg.dkimKeyDirectory}"
         '';
+
+  createDhParameterFile = let
+     dovecotVersion = builtins.fromJSON
+       (builtins.readFile (pkgs.callPackage ./dovecot-version.nix {}));
+    in lib.optionalString
+      (dovecotVersion.major == 2 && dovecotVersion.minor >= 3)
+      ''
+        # Create a dh parameter file
+        if [ ! -s "${cfg.certificateDirectory}/dh.pem" ]
+        then
+            mkdir -p "${cfg.certificateDirectory}"
+            ${pkgs.openssl}/bin/openssl \
+                  dhparam ${builtins.toString cfg.dhParamBitLength} \
+                  > "${cfg.certificateDirectory}/dh.pem"
+        fi
+      '';
+
+  preliminarySelfsigned = config.security.acme.preliminarySelfsigned;
+  acmeWantsTarget = [ "acme-certificates.target" ]
+    ++ (lib.optional preliminarySelfsigned "acme-selfsigned-certificates.target");
+  acmeAfterTarget = if preliminarySelfsigned
+    then [ "acme-selfsigned-certificates.target" ]
+    else [ "acme-certificates.target" ];
 in
 {
   config = with cfg; lib.mkIf enable {
-    # Make sure postfix gets started first, so that the certificates are in place
-    systemd.services.dovecot2.after = [ "postfix.service" ];
+    # Add target for when certificates are available
+    systemd.targets."mailserver-certificates" = {
+      wants = lib.mkIf (cfg.certificateScheme == 3) acmeWantsTarget;
+      after = lib.mkIf (cfg.certificateScheme == 3) acmeAfterTarget;
+    };
 
-    # Create certificates and maildir folder
-    systemd.services.postfix = {
-      after = (if (certificateScheme == 3) then [ "nginx.service" ] else []);
-      preStart =
-      ''
-      # Create mail directory and set permissions. See
-      # <http://wiki2.dovecot.org/SharedMailboxes/Permissions>.
-      mkdir -p "${mailDirectory}"
-      chgrp "${vmailGroupName}" "${mailDirectory}"
-      chmod 02770 "${mailDirectory}"
+    # Create self signed certificate
+    systemd.services.mailserver-selfsigned-certificate = lib.mkIf (cfg.certificateScheme == 2) {
+      wantedBy = [ "mailserver-certificates.target" ];
+      after    = [ "local-fs.target" ];
+      before   = [ "mailserver-certificates.target" ];
+      script = ''
+        # Create certificates if they do not exist yet
+        dir="${cfg.certificateDirectory}"
+        fqdn="${cfg.fqdn}"
+        case $fqdn in /*) fqdn=$(cat "$fqdn");; esac
+        key="''${dir}/key-${cfg.fqdn}.pem";
+        cert="''${dir}/cert-${cfg.fqdn}.pem";
 
-        ${create_certificate}
-
-        ${let
-           dovecotVersion = builtins.fromJSON
-             (builtins.readFile (pkgs.callPackage ./dovecot-version.nix {}));
-          in lib.optionalString
-            (dovecotVersion.major == 2 && dovecotVersion.minor >= 3)
-            createDhParameterFile}
+        if [ ! -f "''${key}" ] || [ ! -f "''${cert}" ]
+        then
+            mkdir -p "${cfg.certificateDirectory}"
+            (umask 077; "${pkgs.openssl}/bin/openssl" genrsa -out "''${key}" 2048) &&
+                "${pkgs.openssl}/bin/openssl" req -new -key "''${key}" -x509 -subj "/CN=''${fqdn}" \
+                        -days 3650 -out "''${cert}"
+        fi
       '';
+      serviceConfig = {
+        Type = "oneshot";
+        PrivateTmp = true;
+      };
+    };
+
+    # Create maildir folder and dh parameters before dovecot startup
+    systemd.services.dovecot2 = {
+      after = [ "mailserver-certificates.target" ];
+      wants = [ "mailserver-certificates.target" ];
+      preStart = ''
+        # Create mail directory and set permissions. See
+        # <http://wiki2.dovecot.org/SharedMailboxes/Permissions>.
+        mkdir -p "${mailDirectory}"
+        chgrp "${vmailGroupName}" "${mailDirectory}"
+        chmod 02770 "${mailDirectory}"
+
+        ${createDhParameterFile}
+      '';
+    };
+
+    # Postfix requires rmilter socket, dovecot lmtp socket, dovecot auth socket and certificate to work
+    systemd.services.postfix = {
+      after = [ "rmilter.socket" "dovecot2.service" "mailserver-certificates.target" ];
+      wants = [ "mailserver-certificates.target" ];
+      requires = [ "rmilter.socket" "dovecot2.service" ];
     };
 
     # Create dkim certificates