Improve TileJSON response with CDN and 2x tiles

[maxmalynowsky]

Problem description

👋 Hey all!

I have TiTiler deployed on an Azure Container App behind a CDN, serving as the backend to a few MapLibre GL maps. The easiest way for me to add data to the maps would be to get a TileJSON, but there are two issues I encountered. This is an example URL I would try:

Request:

https://titiler-cdn.mydomain.com/cog/tilejson.json?tile_format=webp&tile_scale=2&url=https://data.mydomain.com/data.tif

Response:

{
  "tilejson": "2.2.0",
  "version": "1.0.0",
  "scheme": "xyz",
  "tiles": [
    "http://myapp.azurecontainerapps.io/cog/tiles/WebMercatorQuad/{z}/{x}/{y}@2x.webp?url=https%3A%2F%2Fmydomain.com%2Fdata.tif"
  ],
  "minzoom": 8,
  "maxzoom": 15,
  "bounds": [-1, -1, 1, 1],
  "center": [0, 0, 8]
}

Issues:

1. The URL in tiles property comes from the URL my container is deployed to in Azure, but I'd like it to use the request origin of the CDN instead. I'm a bit new at developing with Starlette / FastAPI / TiTiler, so I'm not sure if there's a way to set this as an ENV property anywhere, which would be ideal. Otherwise, I wouldn't mind being able to set a tile_url property such as https://titiler-cdn.mydomain.com in the query to specify this.
2. In this example, my GeoTIFF can be tiled down to zoom 15 with 256px tiles. However, using 512px tiles, it should have a max zoom of 14. I made an edit suggesting the way this could be implemented, but I'm still figuring out how to set this up locally to test.

[vincentsarago]

@maxmalynowsky can you check #342 and see if you find useful information

[maxmalynowsky]

Hi @vincentsarago , thanks for the link, but setting root_path doesn't address the problem I'm having.

I'm not looking to change https://mydomain.com/cog/tilejson.json to https://mydomain.com/api/v1/cog/tilejson.json
but rather to change http://azureapp.io/cog/tilejson.json to https://mydomain.com/cog/tilejson.json

After doing more research into this, it seems my issue comes from Starlette's request.base_url as used here in making an absolute URL. I'm guessing the solution would need to come from implementing custom middleware to set request._base_url to the URL I want to have included in the tilejson response. I realize this is unrelated to titiler and not something that's likely easy to implement, although if you've seen a potential fix for this it would really help.

[vincentsarago]

there is also this discussion #345 (comment) which could be useful

[maxmalynowsky]

I saw that issue, unfortunately --forwarded-allow-ips=* didn't result in a change. Worryingly, setting that also failed to change the scheme of my request from http to https. This issue seems like it is the closest to solving what I needed, but implementing it had no effect: https://stackoverflow.com/questions/64600957/fastapi-set-the-url-or-path-for-the-request-object

[vincentsarago]

Not sure if it helps, but in AWS I remember I had to do this 👇