How to avoid upstream timeouts?

Ok I just set it to 6 workers (as I have a Linode 8096: 8 GB RAM, 6 CPU Cores, 192 GB SSD Storage https://www.linode.com/pricing)

env:
  LANG: en_US.UTF-8
  ## TODO: How many concurrent web requests are supported?
  ## With 2GB we recommend 3-4 workers, with 1GB only 2
  UNICORN_WORKERS: 6
  ##
  ## TODO: List of comma delimited emails that will be made admin and developer
  ## on initial signup example 'user1@example.com,user2@example.com'
  DISCOURSE_DEVELOPER_EMAILS: 'hello@nomadlist.io'
  ##
  ## TODO: The domain name this Discourse instance will respond to
  DISCOURSE_HOSTNAME: 'nomadforum.io'
  ##

Then I rebuild it: /var/discourse/launcher rebuild app

Which took a few minutes and then it was up again. But I’m still getting timeouts:

2015/11/11 22:33:24 [error] 11980#0: *19753 upstream timed out (110: Connection timed out) while reading response header from upstream, client: 110.139.184.21, server: nomadforum.io, request: "POST /message-bus/8bd73af468ec44a2ae75ec6534a44696/poll? HTTP/1.1", upstream: "http://127.0.0.1:4578/message-bus/8bd73af468ec44a2ae75ec6534a44696/poll?", host: "nomadforum.io", referrer: "https://nomadforum.io/t/how-to-make-a-macbook-air-ergonomic/5090"
2015/11/11 22:33:27 [error] 11985#0: *23174 upstream timed out (110: Connection timed out) while reading response header from upstream, client: 201.37.160.13, server: nomadforum.io, request: "POST /message-bus/f8bab6397d4b46bca04f91664627c7e9/poll? HTTP/1.1", upstream: "http://127.0.0.1:4578/message-bus/f8bab6397d4b46bca04f91664627c7e9/poll?", host: "nomadforum.io", referrer: "https://nomadforum.io/t/can-you-create-a-foreign-company-and-hire-yourself-as-an-employee/5172"
2015/11/11 22:33:39 [error] 11980#0: *19753 upstream timed out (110: Connection timed out) while reading response header from upstream, client: 110.139.184.21, server: nomadforum.io, request: "POST /message-bus/8bd73af468ec44a2ae75ec6534a44696/poll? HTTP/1.1", upstream: "http://127.0.0.1:4578/message-bus/8bd73af468ec44a2ae75ec6534a44696/poll?", host: "nomadforum.io", referrer: "https://nomadforum.io/t/how-to-make-a-macbook-air-ergonomic/5090"
2015/11/11 22:33:47 [error] 11985#0: *23174 upstream timed out (110: Connection timed out) while reading response header from upstream, client: 201.37.160.13, server: nomadforum.io, request: "POST /message-bus/f8bab6397d4b46bca04f91664627c7e9/poll? HTTP/1.1", upstream: "http://127.0.0.1:4578/message-bus/f8bab6397d4b46bca04f91664627c7e9/poll?", host: "nomadforum.io", referrer: "https://nomadforum.io/t/can-you-create-a-foreign-company-and-hire-yourself-as-an-employee/5172"

Any idea how I can debug this further? Here’s a (filtered) print from my htop. At least I’m seeing 6 workers now, that’s good:

  PID USER      PRI  NI  VIRT   RES   SHR S CPU% MEM%   TIME+  Command
18587 nobody     20   0  394M 83116 65048 S 11.8  1.0  0:08.59 php-fpm: pool www
 4432 mysql      20   0 3372M 83032     0 S  0.7  1.0  4:08.74 /usr/sbin/mysqld
 4436 mysql      20   0 3372M 83032     0 S  0.0  1.0  3:00.56 /usr/sbin/mysqld
 4224 mysql      20   0 3372M 83032     0 S  0.0  1.0  3h02:41 /usr/sbin/mysqld
11985 www-data   20   0  117M 34704  4608 S  1.3  0.4  0:12.70 nginx: worker process
22228 www-data   20   0  118M  4472  2784 S  0.7  0.1  0:00.44 nginx: worker process
22230 www-data   20   0  119M  4844  2932 S  0.0  0.1  0:00.86 nginx: worker process
22349 pymcrdkib  20   0  466M  215M 10280 S  0.0  2.7  0:14.37 unicorn worker[0] -E production -c config/unicorn.conf.rb
22766 pymcrdkib  20   0  464M  216M 10160 S  0.0  2.7  0:11.96 unicorn worker[1] -E production -c config/unicorn.conf.rb
22899 pymcrdkib  20   0  462M  217M 10032 S  0.7  2.7  0:12.13 unicorn worker[2] -E production -c config/unicorn.conf.rb
23241 pymcrdkib  20   0  462M  216M 10108 S  0.7  2.7  0:12.58 unicorn worker[3] -E production -c config/unicorn.conf.rb
23603 pymcrdkib  20   0 1020M  228M 15668 S  1.3  2.9  0:13.10 unicorn worker[4] -E production -c config/unicorn.conf.rb
23809 pymcrdkib  20   0  414M  171M  9752 S  0.7  2.1  0:11.15 unicorn worker[5] -E production -c config/unicorn.conf.rb
22327 pymcrdkib  20   0 1294M  272M 15704 S  0.0  3.4  0:41.49 sidekiq 3.5.0 discourse [0 of 5 busy]
22308 pymcrdkib  20   0 1294M  272M 15704 S  0.0  3.4  5:16.87 sidekiq 3.5.0 discourse [0 of 5 busy]
22238 messagebu  20   0  377M 10768  9384 S  0.0  0.1  0:00.43 postgres: wal writer process
 3382 root       20   0 67900     8     4 S  0.0  0.0  0:00.00 su couchdb -c /usr/bin/couchdb
22210 mysql      20   0  173M  139M  2692 S  0.0  1.7  0:18.25 /usr/bin/redis-server *:6379
16603 root       20   0  134M 18948  4196 S  0.0  0.2  5:33.98 /usr/bin/irssi
18570 nobody     20   0  437M 75224 16592 S  0.0  0.9  0:11.23 php-fpm: pool www
18718 nobody     20   0  429M 96024 44976 S  0.0  1.2  0:03.55 php-fpm: pool www

Load average: load average: 0.77 1.11 1.49

Seems OK too. Can I optimize something else?