Merge branch 'protobuf-from-source' into 'master'

Instructions for installing google-protobuf from source

See merge request !9665

doc/install/google-protobuf.md

+# Installing a locally compiled google-protobuf gem
+
+First we must find the exact version of google-protobuf that your
+GitLab installation requires.
+
+    cd /home/git/gitlab
+
+    # Only one of the following two commands will print something. It
+    # will look like: * google-protobuf (3.2.0)
+    bundle list | grep google-protobuf
+    bundle check | grep google-protobuf
+
+Below we use `3.2.0` as an example. Replace it with the version number
+you found above.
+
+    cd /home/git/gitlab
+    sudo -u git -H gem install google-protobuf --version 3.2.0 --platform ruby
+
+Finally, you can test whether google-protobuf loads correctly. The
+following should print 'OK'.
+
+    sudo -u git -H bundle exec ruby -rgoogle/protobuf -e 'puts :OK'
+
+If the `gem install` command fails you may need to install developer
+tools. On Debian: `apt-get install build-essential libgmp-dev`, on
+Centos/RedHat `yum groupinstall 'Development Tools'`.

doc/install/installation.md

@@ -658,6 +658,12 @@ misconfigured gitlab-workhorse instance. Double-check that you've
 [installed Go](#3-go), [installed gitlab-workhorse](#install-gitlab-workhorse),
 and correctly [configured Nginx](#site-configuration).
 
+### google-protobuf "LoadError: /lib/x86_64-linux-gnu/libc.so.6: version `GLIBC_2.14' not found"
+
+This can happen on some platforms for some versions of the
+google-protobuf gem. The workaround is to [install a source-only
+version of this gem](google-protobuf.md).
+
 [RVM]: https://rvm.io/ "RVM Homepage"
 [rbenv]: https://github.com/sstephenson/rbenv "rbenv on GitHub"
 [chruby]: https://github.com/postmodern/chruby "chruby on GitHub"