Add documentation about AWS region (#213)

Author: kylebarron

docs/troubleshooting/aws.md

@@ -0,0 +1,84 @@
+# Troubleshooting Amazon S3
+
+## Region required
+
+All requests to S3 must include the region. An error will occur on requests when you don't pass the correct region.
+
+For example, trying to list the [`sentinel-cogs`](https://registry.opendata.aws/sentinel-2-l2a-cogs/) open bucket without passing a region will fail:
+
+```py
+import obstore as obs
+from obstore.store import S3Store
+
+store = S3Store("sentinel-cogs", skip_signature=True)
+next(obs.list(store))
+```
+
+raises (note, the error text may change in the future)
+
+```
+GenericError: Generic {
+    store: "S3",
+    source: ListRequest {
+        source: BareRedirect,
+    },
+}
+```
+
+We can fix this by passing the correct region:
+
+```py
+import obstore as obs
+from obstore.store import S3Store
+
+store = S3Store("sentinel-cogs", skip_signature=True, region="us-west-2")
+next(obs.list(store))
+```
+
+this prints:
+
+```py
+[{'path': 'sentinel-s2-l2a-cogs/1/C/CV/2018/10/S2B_1CCV_20181004_0_L2A/AOT.tif',
+  'last_modified': datetime.datetime(2020, 9, 30, 20, 25, 56, tzinfo=datetime.timezone.utc),
+  'size': 50510,
+  'e_tag': '"2e24c2ee324ea478f2f272dbd3f5ce69"',
+  'version': None},
+...
+```
+
+### Inferring the bucket region
+
+Note that it's possible to infer the S3 bucket region from an arbitrary `HEAD` request.
+
+Here, we show an example of using `requests` to find the bucket region, but you can use any HTTP client:
+
+```py
+import requests
+
+def find_bucket_region(bucket_name: str) -> str:
+    resp = requests.head(f"https://{bucket_name}.s3.amazonaws.com")
+    return resp.headers["x-amz-bucket-region"]
+```
+
+Applying this to our previous example, we can use this to find the region of the `sentinel-cogs` bucket:
+
+```py
+find_bucket_region("sentinel-cogs")
+# 'us-west-2'
+```
+
+Or we can pass this directly into the region:
+
+```py
+bucket_name = "sentinel-cogs"
+store = S3Store(
+    bucket_name, skip_signature=True, region=find_bucket_region(bucket_name)
+)
+```
+
+Finding the bucket region in this way works **both for public and non-public buckets**.
+
+This `HEAD` request can also tell you if the bucket is public or not by checking the [HTTP response code](https://developer.mozilla.org/en-US/docs/Web/HTTP/Status) (accessible in `requests` via [`resp.status_code`](https://requests.readthedocs.io/en/latest/api/#requests.Response.status_code)):
+
+- [`200`](https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/200): public bucket.
+- [`403`](https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/403): private bucket.

mkdocs.yml

@@ -48,6 +48,8 @@ nav:
       - api/exceptions.md
       - api/file.md
       - fsspec Integration: api/fsspec.md
+  - Troubleshooting:
+      - AWS: troubleshooting/aws.md
   - Advanced:
       - advanced/pickle.md
   - Developer Docs: