mixins: Normalize headless service name for query-frontend/scheduler (#…

…8880)

**What this PR does / why we need it**:
Mixins in general are rather complex pieces of code to consume. When
trying to use the loki mixins it wasn't apparent at first that I could
use a headless service for DNS SRV discovery for both query_frontend and
query_scheduler, especially because for frontend the service is named
`query_frontend_headless_service` and for the scheduler, it's named
`query_scheduler_service_discovery`. Furthermore, the query_frontend
mixin provides a non-headless version of the service while
query_scheduler doesn't. This PR aims at normalizing this for end users,
both headless services are now named `query_frontend_headless_service`
and `query_scheduler_headless_service` and both also provide a
non-headless version of the service.

CHANGELOG.md

@@ -101,6 +101,7 @@
 
 * [7923](https://github.com/grafana/loki/pull/7923) **manohar-koukuntla**: Add zone aware ingesters in jsonnet deployment
 * [8855](https://github.com/grafana/loki/pull/8855) **JoaoBraveCoding**: Add gRPC port to loki compactor mixin
+* [8880](https://github.com/grafana/loki/pull/8880) **JoaoBraveCoding**: Normalize headless service name for query-frontend/scheduler
 
 ##### Fixes
 

production/ksonnet/loki/common.libsonnet

@@ -32,6 +32,12 @@ local k = import 'ksonnet-util/kausal.libsonnet';
     // This helps ensure we create SRV records starting with _grpclb
     grpclbServiceFor(deployment):: k.util.serviceFor(deployment, $._config.service_ignored_labels, nameFormat='%(port)s'),
 
+    // Headless service for discovering IPs of pods instead of the service IP.
+    headlessService(deployment, name)::
+      $.util.grpclbServiceFor(deployment) +
+      k.core.v1.service.mixin.spec.withClusterIp('None') +
+      k.core.v1.service.mixin.spec.withPublishNotReadyAddresses(true) +
+      k.core.v1.service.mixin.metadata.withName(name),
 
     readinessProbe::
       container.mixin.readinessProbe.httpGet.withPath('/ready') +

production/ksonnet/loki/query-frontend.libsonnet

@@ -47,17 +47,17 @@ local k = import 'ksonnet-util/kausal.libsonnet';
   // so if the intention is to use the k8s service for load balancing,
   // it is advised to use the below `query-frontend` service instead.
   query_frontend_headless_service:
-    $.util.grpclbServiceFor($.query_frontend_deployment) +
-    // Make sure that query frontend worker, running in the querier, do resolve
-    // each query-frontend pod IP and NOT the service IP. To make it, we do NOT
-    // use the service cluster IP so that when the service DNS is resolved it
-    // returns the set of query-frontend IPs.
-    service.mixin.spec.withClusterIp('None') +
-    // Query frontend will not become ready until at least one querier connects
-    // which creates a chicken and egg scenario if we don't publish the
-    // query-frontend address before it's ready.
-    service.mixin.spec.withPublishNotReadyAddresses(true) +
-    service.mixin.metadata.withName('query-frontend-headless'),
+    // headlessService will make ensure two things:
+    //   1. Set clusterIP to "None": this makes it so that query frontend worker,
+    //      running in the querier, resolve each query-frontend pod IP instead
+    //      of the service IP. clusterIP set to "None" allow this by making it
+    //      so that when the service DNS is resolved it returns the set of
+    //      query-frontend IPs.
+    //   2. Set withPublishNotReadyAddresses to true: query frontend will not
+    //      become ready until at least one querier connects which creates a
+    //      chicken and egg scenario if we don't publish the query-frontend
+    //      address before it's ready.
+    $.util.headlessService($.query_frontend_deployment, 'query-frontend-headless'),
 
   query_frontend_service:
     $.util.grpclbServiceFor($.query_frontend_deployment),

production/ksonnet/loki/query-scheduler.libsonnet

@@ -61,10 +61,29 @@ local k = import 'ksonnet-util/kausal.libsonnet';
 
   local service = k.core.v1.service,
 
-  // Headless to make sure resolution gets IP address of target pods, and not service IP.
-  query_scheduler_discovery_service: if !$._config.query_scheduler_enabled then {} else
-    $.util.grpclbServiceFor($.query_scheduler_deployment) +
-    service.mixin.spec.withPublishNotReadyAddresses(true) +
-    service.mixin.spec.withClusterIp('None') +
-    service.mixin.metadata.withName('query-scheduler-discovery'),
+  // When this module was created the headless service was named
+  // 'query-scheduler-discovery' which diverges from the naming convention in
+  // query-frontend, this hidden attribute provides backward compatibility while
+  // allowing users to solve themselves this inconsistency
+  query_scheduler_headless_service_name:: 'query-scheduler-discovery',
+
+  // A headless service for discovering IPs of each query-scheduler pod.
+  // It leaves it up to the client to do any load-balancing of requests,
+  // so if the intention is to use the k8s service for load balancing,
+  // it is advised to use the below `query-scheduler` service instead.
+  query_scheduler_headless_service: if !$._config.query_scheduler_enabled then {} else
+    // headlessService will make ensure two things:
+    //   1. Set clusterIP to "None": this makes it so that query scheduler worker,
+    //      running in the querier, resolve each query-scheduler pod IP instead
+    //      of the service IP. clusterIP set to "None" allow this by making it
+    //      so that when the service DNS is resolved it returns the set of
+    //      query-scheduler IPs.
+    //   2. Set withPublishNotReadyAddresses to true: query scheduler will not
+    //      become ready until at least one querier connects which creates a
+    //      chicken and egg scenario if we don't publish the query-scheduler
+    //      address before it's ready.
+    $.util.headlessService($.query_scheduler_deployment, $.query_scheduler_headless_service_name),
+
+  query_scheduler_service: if !$._config.query_scheduler_enabled then {} else
+    $.util.grpclbServiceFor($.query_scheduler_deployment),
 }