http://10.10.21.38/osm_tiles/0/0/0.png not found

tail -f /var/log/apache2/error.log

Thu Mar 28 07:35:03.001960 2019] [mpm_prefork:notice] [pid 12824] AH00163: Apache/2.4.18 (Ubuntu) configured -- resuming normal operations
[Thu Mar 28 07:35:03.001998 2019] [core:notice] [pid 12824] AH00094: Command line: '/usr/sbin/apache2'
[Thu Mar 28 10:55:33.880692 2019] [mpm_prefork:notice] [pid 12824] AH00171: Graceful restart requested, doing restart
[Thu Mar 28 10:55:33.956871 2019] [so:warn] [pid 12824] AH01574: module tile_module is already loaded, skipping
[Thu Mar 28 10:55:33.959605 2019] [tile:notice] [pid 12824] Loading tile config default at /osm_tiles/ for zooms 0 - 20 from tile directory /var/lib/mod_tile with extension .png and mime type image/png
[Thu Mar 28 10:55:33.959645 2019] [tile:notice] [pid 12824] Loading tile config default at /osm_tiles/  for zooms 0 - 20 from tile directory /var/lib/mod_tile/ with extension .png and mime type image/png
AH00558: apache2: Could not reliably determine the server's fully qualified domain name, using 127.0.1.1. Set the 'ServerName' directive globally to suppress this message
[Thu Mar 28 10:55:34.000252 2019] [mpm_prefork:notice] [pid 12824] AH00163: Apache/2.4.18 (Ubuntu) configured -- resuming normal operations
[Thu Mar 28 10:55:34.000286 2019] [core:notice] [pid 12824] AH00094: Command line: '/usr/sbin/apache2'

/etc/apache2/sites-enabled/osm_tiles.conf*

<VirtualHost *:80>

        ServerName 10.10.21.38
        ServerAdmin webmaster@10.10.21.38

                  CustomLog /var/log/apache2/default_access.log common
                  ErrorLog /var/log/apache2/default_error.log

                  LoadModule tile_module /usr/lib/apache2/modules/mod_tile.so

                  AddTileConfig /osm_tiles/ default
                  LoadTileConfigFile /usr/local/etc/renderd.conf
                  ModTileTileDir /var/lib/mod_tile
                  ModTileRenderdSocketName /var/run/renderd/renderd.sock
                  ModTileRequestTimeout 0
                  ModTileMissingRequestTimeout 30


                  DocumentRoot "/var/www/osm_tiles/"

                  <Directory "/var/www/osm_tiles/">
                          AllowOverride None
                          Options None
                          Order allow,deny
                          Allow from all
                  </Directory>

                  Alias /osm_tiles "/var/www/osm_tiles"

                  <Directory "/var/www/osm_tiles/">
                          AllowOverride None
                          Options None
                          Order allow,deny
                    </Directory>

                  LogLevel debug
</VirtualHost>

/usr/local/etc/renderd.conf

[renderd]
socketname=/var/run/renderd/renderd.sock
num_threads=4
tile_dir=/var/lib/mod_tile/
stats_file=/var/run/renderd/renderd.stats

;[renderd01]
;iphostname=::1
;ipport=7654
;num_threads=4
;tile_dir=rados://tiles/etc/ceph/ceph.conf
;stats_file=/var/run/renderd/renderd.stats

;[renderd02]
;iphostname=::1
;ipport=7654
;num_threads=8
;tile_dir=memcached://
;stats_file=/var/run/renderd/renderd.stats

[mapnik]
plugins_dir=/usr/lib/mapnik/3.0/input/
font_dir=/usr/share/fonts/truetype
font_dir_recurse=1

[default]
URI=/osm_tiles/
TILEDIR=/var/lib/mod_tile/
XML=/home/osm/openstreetmap-carto-2.41.0/style.xml
HOST=10.10.21.38
TILESIZE=256

;HTCPHOST=proxy.openstreetmap.org
;** config options used by mod_tile, but not renderd **
;MINZOOM=0
;MAXZOOM=18
;TYPE=png image/png
;DESCRIPTION=This is a description of the tile layer used in the tile json request
;ATTRIBUTION=&copy;<a href=\"http://www.openstreetmap.org/\">OpenStreetMap</a> and <a href=\"http://wiki.openstreetmap.org/wiki/Contributors\">contributors</a>, <a href=\"http://opendatacommons.org/licenses/odbl/\">ODbL</a>
;SERVER_ALIAS=http://localhost/
;CORS=http://www.openstreetmap.org
;ASPECTX=1
;ASPECTY=1
;SCALE=1.0

;[style2]
;URI=/osm_tiles2/
;TILEDIR=rados://tiles/etc/ceph/ceph.conf
;TILESIZE=512
;XML=/home/jburgess/osm/svn.openstreetmap.org/applications/rendering/mapnik/osm-local2.xml
;HOST=10.10.21.38
;HTCPHOST=proxy.openstreetmap.org
;** config options used by mod_tile, but not renderd **
;MINZOOM=0
;MAXZOOM=22
;TYPE=png image/png
;DESCRIPTION=This is a description of the tile layer used in the tile json request
;ATTRIBUTION=&copy;<a href=\"http://www.openstreetmap.org/\">OpenStreetMap</a> and <a href=\"http://wiki.openstreetmap.org/wiki/Contributors\">contributors</a>, <a href=\"http://opendatacommons.org/licenses/odbl/\">ODbL</a>
;SERVER_ALIAS=http://localhost/
;CORS=*

anyone can you please me on this?

Thanks in advanced.