Merge "HealthCheck Middleware"

specs/liberty/healtcheck-middleware.rst

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+..
+ This work is licensed under a Creative Commons Attribution 3.0 Unported
+ License.
+
+ http://creativecommons.org/licenses/by/3.0/legalcode
+
+======================
+HealthCheck Middleware
+======================
+
+https://blueprints.launchpad.net/glance/+spec/healthcheck-middleware
+
+HealthCheck Middleware provides <SERVER>:<PORT>/healthcheck endpoint. This
+endpoint behaves similar way as it does in Swift[1]. Normal operations returns
+200 OK and if config option disable_path is enabled and that path exists
+it will return 503 DISABLED BY FILE.
+
+
+Problem description
+===================
+
+Currently Glance does not have any reasonable means to provide health check
+information for example to HAProxy. Any such deployment causes extensive
+logging and causes unnecessary operations in the server end (FE. GET request
+to / which leads to version check).
+
+
+Proposed change
+===============
+
+Take advantage of ``oslo.middleware``\ 's healthcheck middleware by:
+
+#. Adding a new paste filter - ``healthcheck``
+#. Adding the new filter to the default Glance API and Registry pipelines
+
+Disabled functionality would allow using a file in the filesystem to return
+503 DISABLED BY FILE response dropping the node from the HAProxy. This would
+allow the nodes disabled to finish their current operations and improve
+maintenance experience in HA deployments.
+
+Alternatives
+------------
+
+Current operations model.
+
+Take Swift's slightly smaller implementation and copy it directly into
+Glance's source tree.
+
+Data model impact
+-----------------
+
+None
+
+REST API impact
+---------------
+
+GET '/healthcheck' 200 OK, 503 DISABLED BY FILE
+
+Security impact
+---------------
+
+None
+
+Notifications impact
+--------------------
+
+None
+
+Other end user impact
+---------------------
+
+None
+
+Performance Impact
+------------------
+
+Potential performance improvement as healthcheck is done quite frequently
+and the middleware is lightweight filter at the start of the pipeline.
+
+Other deployer impact
+---------------------
+
+healthcheck would be added to the the start of the used pipeline to be used.
+Optional disable_path=PATH option would be needed to the config files to
+enable the discreet disable functionality.
+
+Developer impact
+----------------
+
+None
+
+
+Implementation
+==============
+
+Assignee(s)
+-----------
+
+Primary assignee:
+  jokke
+  kamil-rykowski
+
+Core Reviewers:
+  kragniz
+  flaper87
+  icordasc
+
+Work Items
+----------
+
+Code Change
+Tests
+Config Change
+Documentation Change
+
+
+Dependencies
+============
+
+None
+
+
+Testing
+=======
+
+Simple functional tests to verify the responses form the <SRV>:<P>/healthcheck
+
+
+Documentation Impact
+====================
+
+Documentation changes are quite minimal explaining the new config option and
+functionality.
+
+References
+==========
+
+[1] _https://github.com/openstack/swift/blob/master/swift/common/middleware/healthcheck.py