Set net.core.somaxconn kernel parameter for Puma

Set net.core.somaxconn kernel parameter to a value equal or higher then
the default Puma backlog_socket. The default kernel value is 128, which
is lower then the default Puam backlog.

This was done for Unicorn in
https://gitlab.com/gitlab-org/omnibus-gitlab/-/merge_requests/405, but
this was not done for Puma. Installations after GitLab 13.0+ might see
lower throughput if this setting is not raised.

changelogs/unreleased/sh-puma-somaxconn.yml

+---
+title: Set net.core.somaxconn kernel parameter for Puma
+merge_request: 4688
+author:
+type: performance

doc/settings/puma.md

@@ -43,7 +43,7 @@ correspond to those in Puma, and which ones have no corresponding counterpart.
 | `unicorn['pidfile']`                 | `puma['pidfile']`                  |
 | `unicorn['tcp_nopush']`              | n/a                                |
 | `unicorn['backlog_socket']`          | n/a                                |
-| `unicorn['somaxconn']`               | n/a                                |
+| `unicorn['somaxconn']`               | `puma['somaxconn']`                |
 | n/a                                  | `puma['state_path']`               |
 | `unicorn['log_directory']`           | `puma['log_directory']`            |
 | `unicorn['worker_memory_limit_min']` | n/a                                |

files/gitlab-config-template/gitlab.rb.template

@@ -924,6 +924,8 @@ external_url 'GENERATED_EXTERNAL_URL'
 # puma['listen'] = '127.0.0.1'
 # puma['port'] = 8080
 # puma['socket'] = '/var/opt/gitlab/gitlab-rails/sockets/gitlab.socket'
+# puma['somaxconn'] = 1024
+
 # puma['pidfile'] = '/opt/gitlab/var/puma/puma.pid'
 # puma['state_path'] = '/opt/gitlab/var/puma/puma.state'

files/gitlab-cookbooks/gitlab/attributes/default.rb

@@ -508,6 +508,7 @@ default['gitlab']['puma']['log_directory'] = "/var/log/gitlab/puma"
 default['gitlab']['puma']['listen'] = "127.0.0.1"
 default['gitlab']['puma']['port'] = 8080
 default['gitlab']['puma']['socket'] = '/var/opt/gitlab/gitlab-rails/sockets/gitlab.socket'
+default['gitlab']['puma']['somaxconn'] = 1024
 # Path to the puma server Process ID file
 # defaults to /opt/gitlab/var/puma/puma.pid. The install-dir path is set at build time
 default['gitlab']['puma']['pidfile'] = "#{node['package']['install-dir']}/var/puma/puma.pid"

files/gitlab-cookbooks/gitlab/recipes/puma.rb

@@ -117,3 +117,7 @@ consul_service 'rails' do
   port node['gitlab']['puma']['port']
   reload_service false unless node['consul']['enable']
 end
+
+gitlab_sysctl "net.core.somaxconn" do
+  value node['gitlab']['puma']['somaxconn']
+end

spec/chef/recipes/puma_spec.rb

@@ -86,6 +86,10 @@ RSpec.describe 'gitlab::puma with Ubuntu 16.04' do
         max_threads: 4
       )
     end
+
+    it 'creates sysctl files' do
+      expect(chef_run).to create_gitlab_sysctl('net.core.somaxconn').with_value(1024)
+    end
   end
   context 'with custom Puma settings' do