gdal2tiles.py hangs when run in Conda Docker environment
I'm running a Python script inside a Conda-based Docker container that processes geospatial data. The script runs a two step GDAL workflow, it uses gdaldem colorrelief to create a colorized GeoTIFF, and `gdal2tiles.py` to generate map tiles from that result.
Gdaldem completes successfully every time. However, the script hangs indefinitely as soon as it calls `gdal2tiles.py`... It produces no error output, and surprisingly, even the timeout argument in `subprocess.run` does not trigger an exception, the whole process just freezes with these log:
```
2025-08-02 09:53:22,602 - INFO - Successfully created GeoTIFF: /app/geotiffs/skjav/reflectivity/reflectivity_20250802T094500Z.tif
2025-08-02 09:53:22,636 - INFO - Step 1: Colorizing /app/geotiffs/skjav/reflectivity/reflectivity_20250802T094500Z.tif with gdaldem.
2025-08-02 09:53:22,672 - INFO - Successfully colorized GeoTIFF to /app/static/tiles/skjav/reflectivity/20250802T094500Z/colorized.tif
2025-08-02 09:53:22,672 - INFO - Step 2: Generating tiles from /app/static/tiles/skjav/reflectivity/20250802T094500Z/colorized.tif with gdal2tiles.py.
<-- HANGS HERE -->
```
The code snippet in question:
```
try:
logging.info(f"coloring with with gdaldem.")
color_map_content = create_color_map_file(product_config['cmap'], product_config['vmin'],
product_config['vmax'])
with open(color_file_path, 'w') as f:
f.write(color_map_content)
cmd_colorize = ['gdaldem', 'color-relief', geotiff_path, color_file_path, colorized_tiff_path, '-alpha']
subprocess.run(cmd_colorize, check=True, capture_output=True, text=True, timeout=60)
logging.info(f"colored geotiff to {colorized_tiff_path}")
logging.info(f"generating tiles {colorized_tiff_path} with gdal2tiles.py.")
cmd_gdal2tiles = [
'gdal2tiles.py',
'--profile=raster',
'--zoom=5-12',
'--webp-quality=90',
colorized_tiff_path,
output_tile_dir
]
subprocess.run(cmd_gdal2tiles, check=True, capture_output=True, text=True, timeout=180)
logging.info(f"success - {output_tile_dir}")
return output_tile_dir
```
What could cause `gdal2tiles.py` to hang so completely that it ignores the timeout from Python's subprocess module? Is there a known issue with running `gdal2tiles.py` non interactively from a Python script inside a Docker container that could lead to this kind of deadlock?
Ruled out Environment Path Issues: I added a diagnostic log (`shutil.which('gdal2tiles.py')`) which confirmed the script is correctly finding the modern version of `gdal2tiles.py` inside the conda environment (`/opt/conda/envs/radar-env/bin/gdal2tiles.py`).
Ruled out Multiprocessing: The hang occurs even with the `--processes` flag removed from the command.
Ruled out output format: The hang persists whether I use `--webp-quality=90` or remove it to default to png tiles.
I also tried to replaced subprocess.run with the lower-level `subprocess.Popen` and `proc.communicate(timeout=)` this also hung and failed to trigger the `TimeoutExpired` exception.
