Add optional healthcheck middleware

This change introduces a new option, [healthcheck] enabled, which
enables the healthcheck middleware in mistral-api pipeline.

This middleware allows status check at /healthcheck path, which is
useful for load balancers or any monitoring services to validate health
of its backend services.

This change is created based on the same change proposed to ironic[1].

[1] 6f439414bdcef9fc02f844f475ec798d48d42558

Co-Authored-By: Jim Rollenhagen <jim@jimrollenhagen.com>
Change-Id: I9bf3de8a5ae6a8c9346285147732b773a3667f7e

mistral/api/app.py

@@ -15,7 +15,8 @@
 
 from oslo_config import cfg
 import oslo_middleware.cors as cors_middleware
-import oslo_middleware.http_proxy_to_wsgi as http_proxy_to_wsgi_middleware
+from oslo_middleware import healthcheck
+from oslo_middleware import http_proxy_to_wsgi
 import osprofiler.web
 import pecan
 
@@ -85,7 +86,11 @@ def setup_app(config=None):
         )
 
     # Create HTTPProxyToWSGI wrapper
-    app = http_proxy_to_wsgi_middleware.HTTPProxyToWSGI(app, cfg.CONF)
+    app = http_proxy_to_wsgi.HTTPProxyToWSGI(app, cfg.CONF)
+
+    # Create a healthcheck wrapper
+    if cfg.CONF.healthcheck.enabled:
+        app = healthcheck.Healthcheck(app, cfg.CONF)
 
     # Create a CORS wrapper, and attach mistral-specific defaults that must be
     # included in all CORS responses.

mistral/config.py

@@ -705,6 +705,17 @@ yaql_opts = [
     )
 ]
 
+
+healthcheck_opts = [
+    cfg.BoolOpt('enabled',
+                default=False,
+                help=_('Enable the health check endpoint at /healthcheck. '
+                       'Note that this is unauthenticated. More information '
+                       'is available at '
+                       'https://docs.openstack.org/oslo.middleware/latest/'
+                       'reference/healthcheck_plugins.html.')),
+]
+
 CONF = cfg.CONF
 
 LEGACY_ACTION_PROVIDER_GROUP = 'legacy_action_provider'
@@ -723,6 +734,7 @@ ACTION_LOGGING_GROUP = 'action_logging'
 PROFILER_GROUP = profiler.list_opts()[0][0]
 KEYCLOAK_OIDC_GROUP = "keycloak_oidc"
 YAQL_GROUP = "yaql"
+HEALTHCHECK_GROUP = 'healthcheck'
 KEYSTONE_GROUP = "keystone"
 
 
@@ -760,6 +772,7 @@ CONF.register_opts(coordination_opts, group=COORDINATION_GROUP)
 CONF.register_opts(profiler_opts, group=PROFILER_GROUP)
 CONF.register_opts(keycloak_oidc_opts, group=KEYCLOAK_OIDC_GROUP)
 CONF.register_opts(yaql_opts, group=YAQL_GROUP)
+CONF.register_opts(healthcheck_opts, group=HEALTHCHECK_GROUP)
 loading.register_session_conf_options(CONF, KEYSTONE_GROUP)
 
 CLI_OPTS = [
@@ -807,6 +820,7 @@ def list_opts():
         (PROFILER_GROUP, profiler_opts),
         (KEYCLOAK_OIDC_GROUP, keycloak_oidc_opts),
         (YAQL_GROUP, yaql_opts),
+        (HEALTHCHECK_GROUP, healthcheck_opts),
         (ACTION_HEARTBEAT_GROUP, action_heartbeat_opts),
         (ACTION_LOGGING_GROUP, action_logging_opts),
         (None, default_group_opts)

mistral/tests/unit/api/test_oslo_middleware.py

@@ -16,7 +16,8 @@
 
 from mistral.tests.unit.api import base
 from oslo_config import cfg
-from oslo_middleware import http_proxy_to_wsgi as http_proxy_to_wsgi_middleware
+from oslo_middleware import healthcheck
+from oslo_middleware import http_proxy_to_wsgi
 
 
 class TestHTTPProxyToWSGIMiddleware(base.APITest):
@@ -28,15 +29,38 @@ class TestHTTPProxyToWSGIMiddleware(base.APITest):
 
     def setUp(self):
         # Make sure the HTTPProxyToWSGI options are registered
-        cfg.CONF.register_opts(http_proxy_to_wsgi_middleware.OPTS,
+        cfg.CONF.register_opts(http_proxy_to_wsgi.OPTS,
                                'oslo_middleware')
 
         # Enable proxy headers parsing in HTTPProxyToWSGI middleware.
         self.override_config(
             "enable_proxy_headers_parsing",
-            "True",
+            True,
             group='oslo_middleware'
         )
 
         # Create the application.
         super(TestHTTPProxyToWSGIMiddleware, self).setUp()
+
+
+class TestHealthcheckMiddleware(base.APITest):
+    """Test oslo_middleware Healthcheck.
+
+    It checks that oslo_middleware middleware Healthcheck is executed
+    when enabled.
+    """
+
+    def setUp(self):
+        # Make sure the Healthcheck options are registered
+        cfg.CONF.register_opts(healthcheck.OPTS,
+                               'oslo_middleware')
+
+        # Enable healthcheck middleware.
+        self.override_config(
+            "enabled",
+            True,
+            group='healthcheck'
+        )
+
+        # Create the application.
+        super(TestHealthcheckMiddleware, self).setUp()

releasenotes/notes/healthcheck-b2757de5e49a868b.yaml

@@ -0,0 +1,5 @@
+---
+features:
+  - |
+    The new ``[healthcheck] enabled`` option has been added. This option can
+    be used to enable the ``helthcheck`` middleware in mistral-api service.

tools/config/config-generator.mistral.conf

@@ -3,6 +3,7 @@ namespace = mistral.config
 namespace = oslo.db
 namespace = oslo.messaging
 namespace = oslo.middleware.cors
+namespace = oslo.middleware.healthcheck
 namespace = oslo.middleware.http_proxy_to_wsgi
 namespace = keystonemiddleware.auth_token
 namespace = oslo.log