On 17 May 2015 at 16:30, Richard Z. <ricoz....@gmail.com> wrote: > On Sun, May 17, 2015 at 05:09:59PM +0200, Jochen Topf wrote: >> On So, Mai 17, 2015 at 04:46:24 +0200, Maarten Deen wrote: >> > Is it normal that the a, b and c.tile.openstreetmap.org IP-adresses refer >> > to >> > the same server? For me, they all refer to amsterdam.tile.openstreetmap.org >> > and for some reason it is not responding very well (lots of read times out >> > messages in JOSM). >> > To me it would seem more logical to have different tileserveraliases refer >> > to different physical servers. >> >> Thats normal. The a/b/c stuff is a workaround for a "feature" in browsers >> that >> only allow a limited number of connections to the same host at the same time. >> (Modern browsers probably don't have this limitation any more, sombody should >> probably check whether we need the a/b/c stuff any more.) It is not ment to >> be some kind of load-balancing. > > probably doing more harm than good by preventing caching. >
Nope. The tiles server alias (a,b,c) are selected using a hashing algorithm which always selects the same alias for the same tile: https://github.com/Leaflet/Leaflet/blob/master/src/layer/tile/TileLayer.js#L134 (also applies to OpenLayers). Overdue me explaining how the OpenStreetMap Tile CDN works: We have 16 distributed edge cache servers all over the world [1],[2],[3]. These cache servers are monitored in near realtime by pingdom for outages. We use GeoDNS [4] for [a|b|c].tile.openstreetmap.org which points a client to the closest or preferred cache server for the client's region. [5] We rebuild [6] the GeoDNS when pingdom notices an outage, visitors are moved across shortly once their DNS TTL has expired (~5mins) The cache servers use 2 backend rendering servers (orm + yevaud), with one being the preferred server [7] (cache hot path). We monitor the backends similarly with pingdom and GeoDNS updates. The cache servers have a fairness algorithm (token bucket) which ensures that no single client / network can degrade the service for others. The 2x backend rendering servers are near perpetually overloaded, particularly during style updates. The short-term solution would be to add in an additional rendering server, but longer term it would be better to move to a model where tiles (png) are rendered on the edge cache servers with the backend servers producing vector tiles which are pulled by the edge cache servers. There are a few people working on this, but no complete working open source solution ready to go. Some of us on the OSM operations team + a team from Wikimedia are watching developments closely. ;-) 1: http://wiki.openstreetmap.org/wiki/Servers#Other 2: http://dns.openstreetmap.org/tile.openstreetmap.org.html 3: http://wiki.openstreetmap.org/wiki/Servers/Tile_CDN 4: https://github.com/openstreetmap/chef/tree/master/cookbooks/geodns 5: https://git.openstreetmap.org/dns.git/blob/HEAD:/src/tile.openstreetmap 6: https://git.openstreetmap.org/dns.git/blob/HEAD:/bin/mkgeo 7: https://git.openstreetmap.org/dns.git/blob/HEAD:/src/render.openstreetmap Kind regards, Grant Part of the OSM operations team. _______________________________________________ talk mailing list talk@openstreetmap.org https://lists.openstreetmap.org/listinfo/talk
