Lambda function to read COG, maintaining file object outside the handler

readcog_warm.py

import json
import rasterio


# open file as a global
SRC = rasterio.open('s3://bucket/cog.tif') # <<-- THIS LINE HAS MOVED UP FROM THE FUNCTION BELOW :-)

def handler(event, context):
  """Lambda function to read pixel values from a COG"""

  # note: lat, lon extracted from Lambda event object   
  row, col = SRC.index(lon, lat)          # convert coordinates to raster grid
  window = Window(col, row, 1, 1)         # create a window of 1 pixel

  # Set rasterio environment as required
  with rasterio.Env(CPL_CURL_VERBOSE=False, CPL_VSIL_CURL_ALLOWED_EXTENSIONS='.tif', GDAL_DISABLE_READDIR_ON_OPEN='YES'):
    pixel = src.read(window=window)       # read data
    return {                              # return as json object
      'headers': {},
      'body': JSON.dumps(pixel.tolist()) 
    }