Support PostGIS as alternative data source to Overpass

[steinbro]

To use, just set the --backend-url to a postgres:// URL. For example, if you're running the docker-compose setup I added to the Openscape repo a while back, use postgres://postgres:secret@localhost:5432/osm. (You'd also need to specify an alternate --port in this case, since the original tile server in that docker-compose setup also runs on 8080.)

@Oliver2213 if you are spinning up a PostGIS data source, please test this.

Fixes #9

[Oliver2213]

Thanks for this! I tested with the container you mentioned, first using overpass and then switching the backend URL. I get this error:

ERROR:server:request: /tiles/16/18745/25070.json
ERROR:server:[Errno 2] No such file or directory
ERROR:aiohttp.server:Error handling request

It seems to get to the point of opening the connection in query, but then throws that exception.

[steinbro]

That's weird; I didn't change anything that involves writing or reading to files. I'm not able to reproduce this. Maybe this is also Sentry related -- try commenting out the @sentry_sdk.trace decorator in postgis.py? Also, are you running through a Docker container or just a virtualenv?

[Oliver2213]

I'm running it in a docker container. I pulled out all the sentry stuff just to be sure for testing - when I do, I still get the same error. No file name given either. So as far as I can tell it isn't Sentry, and it doesn't seem to be the overpass stuff, since that worked in my tests.

[Oliver2213]

I did track it down to right as it goes to get a connection and a cursor with print statements. I read the diff before testing - yeah, no changes I saw related to files. :(

[steinbro]

Hmm, this might be a bug with aiopg (which the Overpass backend doesn't use): aio-libs/aiopg#837

Seems it might be specific to a particular combination of Python and SSL versions, so you could try installing different versions, or try some of the other workarounds suggested in that thread.

[steinbro]

OK, try again -- I managed to recreate the issue, and I pulled a monkey-patch workaround from the aiopg issue thread linked above that eliminates the error.

[Oliver2213]

Hmm. I re-applied my sentry-removal changes after updating to be sure I was doing the same thing. Now I get this:

======== Running on http://0.0.0.0:8081 ========
(Press CTRL+C to quit)
Connection refused
        Is the server running on that host and accepting TCP/IP connections?
connection to server at "localhost" (::1), port 5432 failed: Cannot assign requested address
        Is the server running on that host and accepting TCP/IP connections?

I'm not sure this isn't just me messing something up here; let me know if you can reproduce this.

[steinbro]

Yes, I also ran into this. if you are running Overscape in a Docker container that's trying to talk to a PostGIS server on the host machine, then the backend hostname should be host.docker.internal rather than localhost.

[Oliver2213]

Hmm. That's what my searching turned up too, but that also didn't seem to work.
After seeing this though and doing more looking, I saw someone mention the internal gateway IP, 172.17.0.1, which did work.
Success!

[Oliver2213]

This looks good to merge if you're ready (caching, any more metrics you'd like) 🎉

[Oliver2213]

❇️