Adding a script to speed up cluster backups on enterprise

Only affects GHE cluster instances. No change for single appliance GHE.
This will not impact GHE instances older than 2.6.
You will need to upgrade to GHE 2.6.8 and 2.7.3 for this enhancement to be available.

This will benefit cluster setups with 3 or more nodes.

Some basic benchmarks:

This test is with roughly 1.2k repos of a total size of 14G.

Legacy script

```
real    4m2.751s
user    1m11.998s
sys     0m44.079s
Repo sync with no pre-calculated routes took 241s
```

New script backing up the repositories

```
real    2m3.509s
user    0m57.403s
sys     0m31.405s

* Transferring 297 repositories from ghe-test-dgit-fs1
* Transferring 304 repositories from ghe-test-dgit-fs2
* Transferring 268 repositories from ghe-test-dgit-fs3
* Transferring 280 repositories from ghe-test-dgit-fs4

Calculating sync routes took 4s
Repo sync with calculated routes took 118s
```

Author: sridharavinash

bin/ghe-backup

@@ -166,8 +166,18 @@ ghe-backup-es-hookshot ||
 failures="$failures hookshot"
 
 echo "Backing up Git repositories ..."
-ghe-backup-repositories-${GHE_BACKUP_STRATEGY} ||
-failures="$failures repositories"
+if [ "$GHE_BACKUP_STRATEGY" = "cluster" ]; then
+  if ghe-ssh "$GHE_HOSTNAME" test -f /data/github/current/bin/dgit-cluster-backup-routes ; then
+    echo "* Using calculated routes method..."
+    ghe-backup-repositories-cluster-ng || failures="$failure repositories"
+  else
+    echo "* Using legacy method. A faster backup method is available on enterprise 2.7 and up."
+    ghe-backup-repositories-cluster || failures="$failures repositories"
+  fi
+else
+  ghe-backup-repositories-${GHE_BACKUP_STRATEGY} ||
+  failures="$failures repositories"
+fi
 
 echo "Backing up GitHub Pages ..."
 ghe-backup-pages-${GHE_BACKUP_STRATEGY} ||

share/github-backup-utils/ghe-backup-repositories-cluster

@@ -51,8 +51,8 @@ backup_current="$GHE_DATA_DIR/current/repositories"
 
 # Verify rsync is available.
 if ! rsync --version 1>/dev/null 2>&1; then
-    echo "Error: rsync not found." 1>&2
-    exit 1
+  echo "Error: rsync not found." 1>&2
+  exit 1
 fi
 
 # Perform a host-check and establish GHE_REMOTE_XXX variables.
@@ -108,28 +108,27 @@ done
 # If we have a previous increment, avoid transferring existing files via rsync's
 # --link-dest support. This also decreases physical space usage considerably.
 if [ -d "$backup_current" ]; then
-    link_dest="--link-dest=../../current/repositories"
+  link_dest="--link-dest=../../current/repositories"
 fi
 
 # Transfer repository data from a GitHub instance to the current snapshot
 # directory, using a previous snapshot to avoid transferring files that have
 # already been transferred. A set of rsync filter rules are provided on stdin
 # for each invocation.
 rsync_repository_data () {
-    port=$(ssh_port_part "$1")
-    host=$(ssh_host_part "$1")
-
-    shift
-    ghe-rsync -av \
-        -e "ssh -q $opts -p $port -F $config_file -l $user" \
-        $link_dest "$@" \
-        --rsync-path='sudo -u git rsync' \
-        --include-from=- --exclude=\* \
-        "$host:$GHE_REMOTE_DATA_USER_DIR/repositories/" \
-        "$backup_dir" 1>&3
+  port=$(ssh_port_part "$1")
+  host=$(ssh_host_part "$1")
+
+  shift
+  ghe-rsync -av \
+    -e "ssh -q $opts -p $port -F $config_file -l $user" \
+    $link_dest "$@" \
+    --rsync-path='sudo -u git rsync' \
+    --include-from=- --exclude=\* \
+    "$host:$GHE_REMOTE_DATA_USER_DIR/repositories/" \
+    "$backup_dir" 1>&3
 }
 
-
 for hostname in $hostnames; do
   bm_start "$(basename $0) - $hostname"
   echo 1>&3
@@ -199,11 +198,11 @@ RULES
 + /*/nw/??/??/??/*/*.git/packed-refs
 RULES
 
-# Sync loose refs and reflogs. This must be performed before object data is
-# transferred to ensure that all referenced objects are included.
-echo 1>&3
-echo "* Transferring refs and reflogs ..."  1>&3
-rsync_repository_data $hostname:122 -z <<RULES
+  # Sync loose refs and reflogs. This must be performed before object data is
+  # transferred to ensure that all referenced objects are included.
+  echo 1>&3
+  echo "* Transferring refs and reflogs ..."  1>&3
+  rsync_repository_data $hostname:122 -z <<RULES
 - /__*__/
 - /info/