PNG / Meta hybrid using mod_tile and renderd

Question

I have my style sheet the way I want, and was able to use generate_tiles_multiprocess.py to generate my png tiles for zoom levels 4-12.

My thought was to have the "big picture" be static png files, and then only query the database when someone zooms in past that since I don't need high detail of deserts, oceans and such. I have been having a hard time though where I can get it to work one way or the other, but it isn't working as I expected.

What I thought was an incoming request would come for tile http://127.0.0.1/tiles/6/5/5.png If that file existed, Apache would serve it up, if it doesn't it would hand off the request to mod_tile / renderd to render the view, which was then stored as a .meta file.

[renderd]
num_threads=8
tile_dir=/home/renderaccount
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

[tiles]
URI=/tiles/
TILEDIR=/home/renderaccount
XML=/home/renderaccount/openstreetmap-carto/mapnik.xml
HOST=*
TILESIZE=256
MAXZOOM=20

Apache conf:

    ServerAdmin webmaster@localhost
    LoadTileConfigFile /usr/local/etc/renderd.conf
    ModTileRenderdSocketName /var/run/renderd/renderd.sock
    ModTileRequestTimeout 10
    ModTileMissingRequestTimeout 50
    DocumentRoot /home/renderaccount/
    LogLevel info 
    ErrorLog ${APACHE_LOG_DIR}/error.log
    CustomLog ${APACHE_LOG_DIR}/access.log combined

Answer 1

You have misunderstood how mod_tile and renderd are supposed to work.

The generate_tiles_multiprocess.py script would not normally be used by someone who wants to set up a tile server.

Instead, you would run a command like render_list which would generate meta tiles for the area and zoom levels specified. These meta tiles contain 8x8 PNG files each but the PNGs are never stored on disk directly. Instead, when a certain tile is requested through the web server, mod_tile will open the requisite .meta file, exrtact the PNG from there, and serve it. Only if the meta file is not there will mod_tile send a request to renderd to create it.

The tile directory that you have built with generate_tiles_multiprocess.py could be used to run a tile server completely without renderd and database - simply point DocumentRoot to your tile directory - but of course that server would be fully static, and not support updating or on-the-fly rendering of tiles.

PNG / Meta hybrid using mod_tile and renderd

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