web and API health check endpoint

Because scholar is primarily a search service, the endpoint does a
pass-through health check to the elasticsearch backend (aka,
es-public-proxy).

2 files changed, 20 insertions, 4 deletions

diff --git a/fatcat_scholar/search.py b/fatcat_scholar/search.py
index be362b7..026c030 100644
--- a/fatcat_scholar/search.py
+++ b/fatcat_scholar/search.py
@@ -415,3 +415,17 @@ def do_fulltext_search(
         query_wall_time_ms=int(query_delta.total_seconds() * 1000),
         results=results,
     )
+
+def es_scholar_index_exists() -> bool:
+    """
+    Checks if the configured back-end elasticsearch index exists.
+    Intended to be used in health checks.
+    """
+    try:
+        resp = es_client.indices.exists(settings.ELASTICSEARCH_QUERY_FULLTEXT_INDEX)
+    except elasticsearch.exceptions.RequestError as e_raw:
+        if e_raw.status_code == 404:
+            return False
+        else:
+            raise e_raw
+    return resp
diff --git a/fatcat_scholar/web.py b/fatcat_scholar/web.py
index 4887aa6..9664474 100644
--- a/fatcat_scholar/web.py
+++ b/fatcat_scholar/web.py
@@ -21,7 +21,7 @@ from starlette.exceptions import HTTPException as StarletteHTTPException
 
 from fatcat_scholar.config import settings, GIT_REVISION
 from fatcat_scholar.hacks import Jinja2Templates, parse_accept_lang
-from fatcat_scholar.search import process_query, FulltextQuery, FulltextHits
+from fatcat_scholar.search import process_query, FulltextQuery, FulltextHits, es_scholar_index_exists
 from fatcat_scholar.schema import ScholarDoc
 
 
@@ -107,15 +107,17 @@ async def root_head() -> Any:
     return Response()
 
 @api.get("/_health", operation_id="get_health")
-async def health() -> Any:
+def health_get() -> Any:
     """
     Checks that connection back to elasticsearch index is working.
     """
+    if not es_scholar_index_exists():
+        raise HTTPException(status_code=503)
     return Response()
 
 @api.head("/_health", include_in_schema=False)
-async def health_head() -> Any:
-    return Response()
+def health_head() -> Any:
+    return health_get()
 
 class HitsModel(BaseModel):
     count_returned: int