diff --git a/src/devices.ml b/src/devices.ml
deleted file mode 100644
index 6173478a..00000000
--- a/src/devices.ml
+++ /dev/null
@@ -1,30 +0,0 @@
-let db_connection caqti_switch :
-    (unit, Caqti_miou.connection) Vifu.Device.device =
-  let f () =
-    let db_uri = Config.Exchangedb_postgres.config in
-    match Caqti_miou_unix.connect ~sw:caqti_switch db_uri with
-    | Error err ->
-        Fmt.failwith "Database connection failure: %a." Caqti_error.pp err
-    | Ok conn -> (
-        match Pg.preflight conn with
-        | Error err ->
-            Fmt.failwith "Database preflight failure: %a." Caqti_error.pp err
-        | Ok () ->
-            Logs.info (fun m -> m "database connection initialized");
-            conn)
-  in
-  let finally (module Conn : Caqti_miou.CONNECTION) = Conn.disconnect () in
-  Vifu.Device.v ~name:"db_connection" ~finally [] f
-
-let keys storage =
-  let f (module Conn : Pg.CONN) () =
-    let (module Fs) =
-      (module struct
-        let t = storage
-      end)
-    in
-    let keys : (module Keys.S) = (module Keys.Make (Conn) (Fs)) in
-    keys
-  in
-  let finally _key = () in
-  Vifu.Device.v ~name:"keys" ~finally [ Vifu.Device.value db_connection ] f
diff --git a/src/mte.ml b/src/mte.ml
index 55da93d9..8b0428f0 100644
--- a/src/mte.ml
+++ b/src/mte.ml
@@ -64,25 +64,6 @@ let routes =
   in
   tos @ status_info @ management
 
-let caqti_get_ok = function
-  | Error e -> Fmt.failwith "%a" Caqti_error.pp e
-  | Ok v -> v
-
-let test (module Conn : Caqti_miou.CONNECTION) =
-  let minus_req =
-    let open Caqti_request.Infix in
-    let open Caqti_type in
-    (t2 int int ->! int) "SELECT ? - ?"
-  in
-  let a = 22 in
-  let b = 17 in
-  let c = Conn.find minus_req (22, 17) |> caqti_get_ok in
-  assert (a - b = c);
-  Logs.app (fun f -> f "%d - %d = %d" a b c);
-  ()
-
-let disconnect (module Conn : Caqti_miou.CONNECTION) = Conn.disconnect ()
-
 module RNG = Mirage_crypto_rng.Fortuna
 
 let () =
@@ -101,31 +82,42 @@ let () =
   @@ fun rng storage (stack, tcp, udp) () ->
   let@ () = fun () -> Mirage_crypto_rng_mkernel.kill rng in
   let@ () = fun () -> Mnet.kill stack in
-  (* -- setup db connection -- *)
   let hed, he = Mnet_happy_eyeballs.create tcp in
   let@ () = fun () -> Mnet_happy_eyeballs.kill hed in
-  let dns = Mnet_dns.create (udp_db, he) in
+  let dns = Mnet_dns.create (udp, he) in
   let t = Mnet_dns.transport dns in
   let@ () = fun () -> Mnet_dns.Transport.kill t in
-  Caqti_miou.Switch.run @@ fun sw ->
-  Logs.app (fun m -> m "Connecting to the database");
-  let db_connection =
-    let config = Caqti_connect_config.default in
-    let r = Caqti_mnet.connect ~config ~sw stack tcp dns db_uri in
-    caqti_get_ok r
-  in
-  let@ () = fun () -> disconnect db_connection in
-  Logs.app (fun m -> m "Connected");
-  test db_connection;
-  Logs.app (fun m -> m "Test OK");
   (* -- *)
-  (* -- start webserver -- *)
-  let devices = [] in
+  Caqti_miou.Switch.run @@ fun sw ->
+  let db_conn =
+    let db_uri = Config.Exchangedb_postgres.config in
+    (* IMPROVE: use caqti pool
+       [connect_pool] with parameter [?post_connect] for preflight *)
+    match Caqti_mnet.connect ~sw stack tcp dns db_uri with
+    | Error err ->
+        Fmt.failwith "Database connection failure: %a." Caqti_error.pp err
+    | Ok conn -> conn
+  in
+  let@ () =
+   fun () ->
+    let (module Conn : Pg.CONN) = db_conn in
+    Conn.disconnect ()
+  in
+  let () = Pg.preflight db_conn in
+  Logs.info (fun m -> m "database connection initialized");
+  (* -- *)
+  let keys : (module Keys.S) =
+    let (module Conn : Pg.CONN) = db_conn in
+    let (module Fs : Fat.FS) =
+      (module struct
+        let t = storage
+      end)
+    in
+    (module Keys.Make (Conn) (Fs))
+  in
+  (* -- *)
   let cfg = Vifu.Config.v Config.Exchange.port in
-  let db_device = Devices.db_connection sw in
-  let keys_device = Devices.keys storage (Vifu.Device.value db_device) in
-  let devices = Vifu.Devices.[ db_device; keys_device ] in
-  Vifu.run ~cfg ~devices tcp routes ()
+  Vifu.run ~cfg tcp routes (db_conn, keys)
 
 (*
   Miou_unix.run @@ fun () ->
diff --git a/src/pg.ml b/src/pg.ml
index 39b29992..39d968dc 100644
--- a/src/pg.ml
+++ b/src/pg.ml
@@ -26,7 +26,12 @@ let preflight =
         "SET search_path TO exchange;";
       ]
   in
-  fun (module Conn : CONN) -> Syntax.list_iter (fun p -> Conn.exec p ()) l
+  fun (module Conn : CONN) ->
+    let r = Syntax.list_iter (fun p -> Conn.exec p ()) l in
+    match r with
+    | Error err ->
+        Fmt.failwith "Database preflight failure: %a." Caqti_error.pp err
+    | Ok () -> ()
 
 let find_signkey =
   let req =