Combine ssh docs and rename the doc

Backport to CE, originally branch 'evn-ssh-clarify-docs

See merge request gitlab-org/gitlab-ee!3753

doc/administration/operations/fast_ssh_key_lookup.md

+# Fast lookup of authorized SSH keys in the database
+
+Regular SSH operations become slow as the number of users grows because OpenSSH
+searches for a key to authorize a user via a linear search. In the worst case,
+such as when the user is not authorized to access GitLab, OpenSSH will scan the
+entire file to search for a key. This can take significant time and disk I/O,
+which will delay users attempting to push or pull to a repository. Making
+matters worse, if users add or remove keys frequently, the operating system may
+not be able to cache the `authorized_keys` file, which causes the disk to be
+accessed repeatedly.
+
+GitLab Shell solves this by providing a way to authorize SSH users via a fast,
+indexed lookup in the GitLab database. This page describes how to enable the fast
+lookup of authorized SSH keys.
+
+> **Warning:** OpenSSH version 6.9+ is required because
+`AuthorizedKeysCommand` must be able to accept a fingerprint. These
+instructions will break installations using older versions of OpenSSH, such as
+those included with CentOS 6 as of September 2017. If you want to use this
+feature for CentOS 6, follow [the instructions on how to build and install a custom OpenSSH package](#compiling-a-custom-version-of-openssh-for-centos-6) before continuing.
+
+## Setting up fast lookup via GitLab Shell
+
+GitLab Shell provides a way to authorize SSH users via a fast, indexed lookup
+to the GitLab database. GitLab Shell uses the fingerprint of the SSH key to
+check whether the user is authorized to access GitLab.
+
+Create the directory `/opt/gitlab-shell` first:
+
+```bash
+sudo mkdir -p /opt/gitlab-shell
+```
+
+Create this file at `/opt/gitlab-shell/authorized_keys`:
+
+```
+#!/bin/bash
+
+if [[ "$1" == "git" ]]; then
+  /opt/gitlab/embedded/service/gitlab-shell/bin/authorized_keys $2
+fi
+```
+
+Set appropriate ownership and permissions:
+
+```
+sudo chown root:git /opt/gitlab-shell/authorized_keys
+sudo chmod 0650 /opt/gitlab-shell/authorized_keys
+```
+
+Add the following to `/etc/ssh/sshd_config` or to `/assets/sshd_config` if you
+are using Omnibus Docker:
+
+```
+AuthorizedKeysCommand /opt/gitlab-shell/authorized_keys %u %k
+AuthorizedKeysCommandUser git
+```
+
+Reload OpenSSH:
+
+```bash
+# Debian or Ubuntu installations
+sudo service ssh reload
+
+# CentOS installations
+sudo service sshd reload
+```
+
+Confirm that SSH is working by removing your user's SSH key in the UI, adding a
+new one, and attempting to pull a repo.
+
+> **Warning:** Do not disable writes until SSH is confirmed to be working
+perfectly because the file will quickly become out-of-date.
+
+In the case of lookup failures (which are not uncommon), the `authorized_keys`
+file will still be scanned. So git SSH performance will still be slow for many
+users as long as a large file exists.
+
+You can disable any more writes to the `authorized_keys` file by unchecking
+`Write to "authorized_keys" file` in the Application Settings of your GitLab
+installation.
+
+![Write to authorized keys setting](img/write_to_authorized_keys_setting.png)
+
+Again, confirm that SSH is working by removing your user's SSH key in the UI,
+adding a new one, and attempting to pull a repo.
+
+Then you can backup and delete your `authorized_keys` file for best performance.
+
+## How to go back to using the `authorized_keys` file
+
+This is a brief overview. Please refer to the above instructions for more context.
+
+1. [Rebuild the `authorized_keys` file](../raketasks/maintenance.md#rebuild-authorized_keys-file)
+1. Enable writes to the `authorized_keys` file in Application Settings
+1. Remove the `AuthorizedKeysCommand` lines from `/etc/ssh/sshd_config` or from `/assets/sshd_config` if you are using Omnibus Docker.
+1. Reload sshd: `sudo service sshd reload`
+1. Remove the `/opt/gitlab-shell/authorized_keys` file
+
+## Compiling a custom version of OpenSSH for CentOS 6
+
+Building a custom version of OpenSSH is not necessary for Ubuntu 16.04 users,
+since Ubuntu 16.04 ships with OpenSSH 7.2.
+
+It is also unnecessary for CentOS 7.4 users, as that version ships with
+OpenSSH 7.4. If you are using CentOS 7.0 - 7.3, we strongly recommend that you
+upgrade to CentOS 7.4 instead of following this procedure. This should be as
+simple as running `yum update`.
+
+CentOS 6 users must build their own OpenSSH package to enable SSH lookups via
+the database. The following instructions can be used to build OpenSSH 7.5:
+
+1. First, download the package and install the required packages:
+
+    ```
+    sudo su -
+    cd /tmp
+    curl --remote-name https://mirrors.evowise.com/pub/OpenBSD/OpenSSH/portable/openssh-7.5p1.tar.gz
+    tar xzvf openssh-7.5p1.tar.gz
+    yum install rpm-build gcc make wget openssl-devel krb5-devel pam-devel libX11-devel xmkmf libXt-devel
+    ```
+
+3. Prepare the build by copying files to the right place:
+
+    ```
+    mkdir -p /root/rpmbuild/{SOURCES,SPECS}
+    cp ./openssh-7.5p1/contrib/redhat/openssh.spec /root/rpmbuild/SPECS/
+    cp openssh-7.5p1.tar.gz /root/rpmbuild/SOURCES/
+    cd /root/rpmbuild/SPECS
+    ```
+
+3. Next, set the spec settings properly:
+
+    ```
+    sed -i -e "s/%define no_gnome_askpass 0/%define no_gnome_askpass 1/g" openssh.spec
+    sed -i -e "s/%define no_x11_askpass 0/%define no_x11_askpass 1/g" openssh.spec
+    sed -i -e "s/BuildPreReq/BuildRequires/g" openssh.spec
+    ```
+
+3. Build the RPMs:
+
+    ```
+    rpmbuild -bb openssh.spec
+    ```
+
+4. Ensure the RPMs were built:
+
+    ```
+    ls -al /root/rpmbuild/RPMS/x86_64/
+    ```
+
+    You should see something as the following:
+
+    ```
+    total 1324
+    drwxr-xr-x. 2 root root   4096 Jun 20 19:37 .
+    drwxr-xr-x. 3 root root     19 Jun 20 19:37 ..
+    -rw-r--r--. 1 root root 470828 Jun 20 19:37 openssh-7.5p1-1.x86_64.rpm
+    -rw-r--r--. 1 root root 490716 Jun 20 19:37 openssh-clients-7.5p1-1.x86_64.rpm
+    -rw-r--r--. 1 root root  17020 Jun 20 19:37 openssh-debuginfo-7.5p1-1.x86_64.rpm
+    -rw-r--r--. 1 root root 367516 Jun 20 19:37 openssh-server-7.5p1-1.x86_64.rpm
+    ```
+
+5. Install the packages. OpenSSH packages will replace `/etc/pam.d/sshd`
+   with its own version, which may prevent users from logging in, so be sure
+   that the file is backed up and restored after installation:
+
+    ```
+    timestamp=$(date +%s)
+    cp /etc/pam.d/sshd pam-ssh-conf-$timestamp
+    rpm -Uvh /root/rpmbuild/RPMS/x86_64/*.rpm
+    yes | cp pam-ssh-conf-$timestamp /etc/pam.d/sshd
+    ```
+
+6. Verify the installed version. In another window, attempt to login to the server:
+
+    ```
+    ssh -v <your-centos-machine>
+    ```
+
+    You should see a line that reads: "debug1: Remote protocol version 2.0, remote software version OpenSSH_7.5"
+
+    If not, you may need to restart sshd (e.g. `systemctl restart sshd.service`).
+
+7.  *IMPORTANT!* Open a new SSH session to your server before exiting to make
+    sure everything is working! If you need to downgrade, simple install the
+    older package:
+
+    ```
+    # Only run this if you run into a problem logging in
+    yum downgrade openssh-server openssh openssh-clients
+    ```

doc/administration/operations/index.md

@@ -14,4 +14,4 @@ that to prioritize important jobs.
 - [Sidekiq MemoryKiller](sidekiq_memory_killer.md): Configure Sidekiq MemoryKiller
 to restart Sidekiq.
 - [Unicorn](unicorn.md): Understand Unicorn and unicorn-worker-killer.
-- [Speed up SSH operations](speed_up_ssh.md)
+- [Speed up SSH operations](fast_ssh_key_lookup.md): Authorize SSH users via a fast, indexed lookup to the GitLab database.

doc/administration/operations/speed_up_ssh.md

-# Speed up SSH operations
-
-## The problem
-
-SSH operations become slow as the number of users grows.
-
-## The reason
-
-OpenSSH searches for a key to authorize a user via a linear search. In the worst case, such as when the user is not authorized to access GitLab, OpenSSH will scan the entire file to search for a key. This can take significant time and disk I/O, which will delay users attempting to push or pull to a repository. Making matters worse, if users add or remove keys frequently, the operating system may not be able to cache the authorized_keys file, which causes the disk to be accessed repeatedly.
-
-## The solution
-
-GitLab Shell provides a way to authorize SSH users via a fast, indexed lookup to the GitLab database. GitLab Shell uses the fingerprint of the SSH key to check whether the user is authorized to access GitLab.
-
-> **Warning:** OpenSSH version 6.9+ is required because `AuthorizedKeysCommand` must be able to accept a fingerprint. These instructions will break installations using older versions of OpenSSH, such as those included with CentOS as of May 2017.
-
-Create this file at `/opt/gitlab-shell/authorized_keys`:
-
-```
-#!/bin/bash
-
-if [[ "$1" == "git" ]]; then
-  /opt/gitlab/embedded/service/gitlab-shell/bin/authorized_keys $2
-fi
-```
-
-Set appropriate ownership and permissions:
-
-```
-sudo chown root:git /opt/gitlab-shell/authorized_keys
-sudo chmod 0650 /opt/gitlab-shell/authorized_keys
-```
-
-Add the following to `/etc/ssh/sshd_config`:
-
-```
-AuthorizedKeysCommand /opt/gitlab-shell/authorized_keys %u %k
-AuthorizedKeysCommandUser git
-```
-
-Reload the sshd service:
-
-```
-sudo service sshd reload
-```
-
-Confirm that SSH is working by removing your user's SSH key in the UI, adding a new one, and attempting to pull a repo.
-
-> **Warning:** Do not disable writes until SSH is confirmed to be working perfectly because the file will quickly become out-of-date.
-
-In the case of lookup failures (which are not uncommon), the `authorized_keys` file will still be scanned. So git SSH performance will still be slow for many users as long as a large file exists.
-
-You can disable any more writes to the `authorized_keys` file by unchecking `Write to "authorized_keys" file` in the Application Settings of your GitLab installation.
-
-![Write to authorized keys setting](img/write_to_authorized_keys_setting.png)
-
-Again, confirm that SSH is working by removing your user's SSH key in the UI, adding a new one, and attempting to pull a repo.
-
-Then you can backup and delete your `authorized_keys` file for best performance.
-
-## How to go back to using the `authorized_keys` file
-
-This is a brief overview. Please refer to the above instructions for more context.
-
-1. Rebuild the `authorized_keys` file. See https://docs.gitlab.com/ce/administration/raketasks/maintenance.html#rebuild-authorized_keys-file
-1. Enable writes to the `authorized_keys` file
-1. Remove the `AuthorizedKeysCommand` lines from `/etc/ssh/sshd_config`
-1. Reload the sshd service
-1. Remove the `/opt/gitlab-shell/authorized_keys` file
+This document was moved to [another location](fast_ssh_key_lookup.md).