initial implementation of a health check route (#1262)

* initial implementation of a health check route

* remove debugging code

* lint

server/common/health.py

@@ -0,0 +1,29 @@
+from http import HTTPStatus
+from flask import make_response, jsonify
+
+from server import __version__ as cellxgene_version
+from server.common.data_locator import DataLocator
+
+
+def _is_accessible(path):
+    if path is None:
+        return True
+
+    try:
+        dl = DataLocator(path)
+        return dl.exists()
+    except RuntimeError:
+        return False
+
+
+def health_check(config):
+    """
+    simple health check - return HTTP response.
+    See https://tools.ietf.org/id/draft-inadarei-api-health-check-01.html
+    """
+    health = {"status": None, "version": "1", "releaseID": cellxgene_version}
+
+    checks = [_is_accessible(config.datapath), _is_accessible(config.dataroot)]
+    health["status"] = "pass" if all(checks) else "fail"
+    code = HTTPStatus.OK if health["status"] == "pass" else HTTPStatus.BAD_REQUEST
+    return make_response(jsonify(health), code, {"Content-Type": "application/health+json"},)