Add a S3 check to healthcheck endpoint

src/ltdproxy/config.py

@@ -4,6 +4,7 @@
 
 import os
 from enum import Enum
+from typing import Optional
 
 from pydantic import BaseSettings, Field, FilePath, HttpUrl, SecretStr
 
@@ -69,6 +70,16 @@ class Configuration(BaseSettings):
 
     rewrites_config_path: FilePath = Field(env="LTDPROXY_REWRITES_CONFIG")
 
+    healthcheck_bucket_key: Optional[str] = Field(
+        None,
+        description=(
+            "A key in the bucket that the healthcheck endpoint will attempt "
+            "to stream. This is an actual bucket key, and is independent "
+            "of the s3_bucket_prefix configuration."
+        ),
+        env="LTDPROXY_S3_HEALTHCHECK_KEY",
+    )
+
 
 config = Configuration(_env_file=os.getenv("LTD_PROXY_ENV"))
 """Configuration for ltd-proxy."""

src/ltdproxy/handlers/healthcheck.py

@@ -1,11 +1,37 @@
 """Handler for the Kubernetes health check."""
 
-from fastapi import APIRouter
+import httpx
+from fastapi import APIRouter, Depends
+from safir.dependencies.http_client import http_client_dependency
+from safir.dependencies.logger import logger_dependency
 from starlette.responses import PlainTextResponse
+from structlog.stdlib import BoundLogger
+
+from ltdproxy.config import config
+from ltdproxy.s3 import Bucket, bucket_dependency
 
 health_router = APIRouter()
 
 
 @health_router.get("/__healthz", name="healthz")
-def healthy() -> PlainTextResponse:
+async def healthy(
+    bucket: Bucket = Depends(bucket_dependency),
+    logger: BoundLogger = Depends(logger_dependency),
+    http_client: httpx.AsyncClient = Depends(http_client_dependency),
+) -> PlainTextResponse:
+    if config.healthcheck_bucket_key:
+        # enter mode for testing S3 streaming
+        stream = await bucket.stream_object(
+            http_client, config.healthcheck_bucket_key
+        )
+        if stream.status_code != httpx.codes.OK:
+            logger.error(
+                "Health check got bad S3 response code",
+                status_code=stream.status_code,
+            )
+            return PlainTextResponse("ERROR", status_code=500)
+        async for _ in stream.aiter_bytes():
+            pass
+        await stream.aclose()
+
     return PlainTextResponse("OK", status_code=200)