Add upgrade guide for 8.2 to 8.3

doc/update/8.2-to-8.3.md

+# From 8.2 to 8.3
+
+**NOTE:** GitLab 8.0 introduced several significant changes related to
+installation and configuration which *are not duplicated here*. Be sure you're
+already running a working version of at least 8.0 before proceeding with this
+guide.
+
+### 0. Double-check your Git version
+
+**This notice applies only to /usr/local/bin/git**
+
+If you compiled Git from source on your GitLab server then please double-check
+that you are using a version that protects against CVE-2014-9390. For six
+months after this vulnerability became known the GitLab installation guide
+still contained instructions that would install the outdated, 'vulnerable' Git
+version 2.1.2.
+
+Run the following command to get your current Git version:
+
+```sh
+/usr/local/bin/git --version
+```
+
+If you see 'No such file or directory' then you did not install Git according
+to the outdated instructions from the GitLab installation guide and you can go
+to the next step 'Stop server' below.
+
+If you see a version string then it should be v1.8.5.6, v1.9.5, v2.0.5, v2.1.4,
+v2.2.1 or newer. You can use the [instructions in the GitLab source
+installation
+guide](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/install/installation.md#1-packages-dependencies)
+to install a newer version of Git.
+
+### 1. Stop server
+
+    sudo service gitlab stop
+
+### 2. Backup
+
+```bash
+cd /home/git/gitlab
+sudo -u git -H bundle exec rake gitlab:backup:create RAILS_ENV=production
+```
+
+### 3. Get latest code
+
+```bash
+sudo -u git -H git fetch --all
+sudo -u git -H git checkout -- db/schema.rb # local changes will be restored automatically
+```
+
+For GitLab Community Edition:
+
+```bash
+sudo -u git -H git checkout 8-3-stable
+```
+
+OR
+
+For GitLab Enterprise Edition:
+
+```bash
+sudo -u git -H git checkout 8-3-stable-ee
+```
+
+### 4. Update gitlab-shell
+
+```bash
+cd /home/git/gitlab-shell
+sudo -u git -H git fetch
+sudo -u git -H git checkout v2.6.8
+```
+
+### 5. Replace gitlab-git-http-server with gitlab-workhorse
+
+Install and compile gitlab-workhorse. This requires [Go
+1.5](https://golang.org/dl) which should already be on your system
+from GitLab 8.1.
+
+```bash
+cd /home/git
+sudo -u git -H git clone https://gitlab.com/gitlab-org/gitlab-workhorse.git
+cd gitlab-workhorse
+sudo -u git -H git checkout 0.4.2
+sudo -u git -H make
+```
+
+Update the GitLab init script and 'default' file.
+
+```
+cd /home/git/gitlab
+sudo cp lib/support/init.d/gitlab /etc/init.d/gitlab
+test -e /etc/default/gitlab && \
+  sudo sed -i.pre-8.2 's/^\([^=]*\)gitlab_git_http_server/\1gitlab_workhorse/' /etc/default/gitlab
+```
+
+Make sure that you also update your **NGINX configuration** to use
+the new gitlab-workhorse.socket file.
+
+### 6. Install libs, migrations, etc.
+
+```bash
+cd /home/git/gitlab
+
+# MySQL installations (note: the line below states '--without postgres')
+sudo -u git -H bundle install --without postgres development test --deployment
+
+# PostgreSQL installations (note: the line below states '--without mysql')
+sudo -u git -H bundle install --without mysql development test --deployment
+
+# Run database migrations
+sudo -u git -H bundle exec rake db:migrate RAILS_ENV=production
+
+# Clean up assets and cache
+sudo -u git -H bundle exec rake assets:clean assets:precompile cache:clear RAILS_ENV=production
+
+# Update init.d script
+sudo cp lib/support/init.d/gitlab /etc/init.d/gitlab
+```
+
+### 7. Update configuration files
+
+#### New configuration options for `gitlab.yml`
+
+There are new configuration options available for [`gitlab.yml`](config/gitlab.yml.example). View them with the command below and apply them manually to your current `gitlab.yml`:
+
+```sh
+git diff origin/8-2-stable:config/gitlab.yml.example origin/8-3-stable:config/gitlab.yml.example
+```
+
+#### Nginx configuration
+
+View changes between the previous recommended Nginx configuration and the
+current one:
+
+```sh
+# For HTTPS configurations
+git diff origin/8-2-stable:lib/support/nginx/gitlab-ssl origin/8-3-stable:lib/support/nginx/gitlab-ssl
+
+# For HTTP configurations
+git diff origin/8-2-stable:lib/support/nginx/gitlab origin/8-3-stable:lib/support/nginx/gitlab
+```
+
+If you are using Apache instead of NGINX please see the updated [Apache templates].
+Also note that because Apache does not support upstreams behind Unix sockets you
+will need to let gitlab-git-http-server listen on a TCP port. You can do this
+via [/etc/default/gitlab].
+
+[Apache templates]: https://gitlab.com/gitlab-org/gitlab-recipes/tree/master/web-server/apache
+[/etc/default/gitlab]: https://gitlab.com/gitlab-org/gitlab-ce/blob/8-3-stable/lib/support/init.d/gitlab.default.example#L34
+
+
+### 8. Use Redis v2.8.0+
+
+Previous versions of GitLab allowed Redis versions >= 2.0 to be used, but
+GitLab 8.3 uses Sidekiq 4.0, which requires Redis 2.8. You can check your Redis version
+with the following command:
+
+    redis-cli info | grep redis_version
+
+If you need to upgrade, see the [installation guide for Redis](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/install/installation.md#6-redis).
+
+### 9. Start application
+
+    sudo service gitlab start
+    sudo service nginx restart
+
+### 10. Check application status
+
+Check if GitLab and its environment are configured correctly:
+
+    sudo -u git -H bundle exec rake gitlab:env:info RAILS_ENV=production
+
+To make sure you didn't miss anything run a more thorough check:
+
+    sudo -u git -H bundle exec rake gitlab:check RAILS_ENV=production
+
+If all items are green, then congratulations, the upgrade is complete!
+
+## Things went south? Revert to previous version (8.2)
+
+### 1. Revert the code to the previous version
+
+Follow the [upgrade guide from 8.1 to 8.2](8.1-to-8.2.md), except for the
+database migration (the backup is already migrated to the previous version).
+
+### 2. Restore from the backup
+
+```bash
+cd /home/git/gitlab
+sudo -u git -H bundle exec rake gitlab:backup:restore RAILS_ENV=production
+```
+
+If you have more than one backup `*.tar` file(s) please add `BACKUP=timestamp_of_backup` to the command above.
+
+## Troubleshooting
+
+### "You appear to have cloned an empty repository."
+
+See the [7.14 to 8.0 update guide](7.14-to-8.0.md#troubleshooting).