gitlab: Optimize raw blob downloading

In slapos we do a lot of automated software rebuild constantly, and thus
there is constant flow of requests to get raw blobs from git service,
e.g. like this

    https://lab.nexedi.com/nexedi/slapos/raw/master/software/wendelin/software.cfg

A lot of requests comes to slapos.git repository and currently gitlab,
out of the box, cannot keep up with that load.

I've prepared patches to offload raw blobs download requests handling
from unicorn (ruby) to gitlab-workhorse (go), and that resulted in ~ 17x
speedup - e.g. previously our std shuttle can handle ~ 70 raw-blob
requests/s and with my changes it is now ~ 1200 requests/s.

The patches were sent upstream

    https://gitlab.com/gitlab-org/gitlab-workhorse/merge_requests/17

and we discussed with GitLab people and made a plan how to proceed
incrementally. It will probably take some time for gitlab team to fully
accept the approach though.

For now we can use our gitlab-workhorse fork. The patches itself are:

    gitlab-workhorse@1b274d0d
    gitlab-workhorse@2beb8c95

/cc @kazuhiko, @jerome, @jm

software/gitlab/software.cfg

@@ -109,9 +109,11 @@ location = ${buildout:parts-directory}/gitlab-shell
 
 [gitlab-workhorse-repository]
 <= git-repository
-repository = https://gitlab.com/gitlab-org/gitlab-workhorse.git
-# 0.4.X + NXD patches
-revision = 0.4.1-10-g0d0bd209eea7441a3b4202c2e00a989cf340ee86
+#repository = https://gitlab.com/gitlab-org/gitlab-workhorse.git
+repository = https://lab.nexedi.com/kirr/gitlab-workhorse.git
+# 0.4.X + NXD patches for blob download speedup
+# (https://gitlab.com/gitlab-org/gitlab-workhorse/merge_requests/17)
+revision = 0.4.1-23-g2beb8c9539433f072e3db540f91f75894ca6b1b0
 location = ${buildout:parts-directory}/gitlab-workhorse
 
 

software/gitlab/template/nginx-gitlab-http.conf.in

@@ -206,6 +206,13 @@ server {
     return 418;
   }
 
+  # access to raw blobs -> @gitlab-workhorse
+  location ~ ^/[\w\.-]+/[\w\.-]+/raw/ {
+    client_max_body_size 0;
+    error_page 418 = @gitlab-workhorse;
+    return 418;
+  }
+
   location @gitlab-workhorse {
     client_max_body_size 0;
     ## If you use HTTPS make sure you disable gzip compression