search: document INDEX_SEARCH_INDEXERS

Author: stefanhengl

docs/admin/deploy/docker-compose/configuration.mdx

@@ -135,13 +135,15 @@ services:
     environment:
       - 'SRC_GIT_SERVERS=2'
       - 'INDEXED_SEARCH_SERVERS=2'
+      - 'INDEXED_SEARCH_INDEXERS=2'
       - 'SEARCHER_URL=1'
       - 'SYMBOLS_URL=1'
 
   sourcegraph-frontend-internal:
     environment:
       - 'SRC_GIT_SERVERS=2'
       - 'INDEXED_SEARCH_SERVERS=2'
+      - 'INDEXED_SEARCH_INDEXERS=2'
       - 'SEARCHER_URL=1'
       - 'SYMBOLS_URL=1'
 ```

docs/admin/deploy/kubernetes/configure.mdx

@@ -82,6 +82,8 @@ RBAC must be enabled in your cluster for the frontend to communicate with other
 
 This will allow the frontend service to discover endpoints for each service replica and communicate with them through the Kubernetes API. Note that this component should only be added if RBAC is enabled in your cluster.
 
+> **If you are not using Kubernetes service discovery (for example, if you are running without RBAC or outside Kubernetes), you must manually configure service endpoints for the frontend.** See [Running Sourcegraph Without Kubernetes Service Discovery](/admin/deploy/without_service_discovery) for instructions.
+
 ---
 
 ## Monitoring stack

docs/admin/deploy/without_service_discovery.mdx

@@ -0,0 +1,15 @@
+# Running Sourcegraph Without Kubernetes Service Discovery
+
+<Callout type="warning">Not settting these environment variables might prevent pods from starting when running without service discovery.</Callout>
+
+If you are deploying Sourcegraph in an environment **without Kubernetes service discovery** (for example, using Docker Compose or single-container Docker), you must manually configure the frontend service to know about the other service replicas. This is typically required when you are not using RBAC or the `service-discovery` component in Kubernetes, or when running outside Kubernetes entirely.
+
+## Required Environment Variables
+
+- INDEXED_SEARCH_INDEXER
+- INDEXED_SEARCH_SERVERS
+- SEARCHER_URL
+- SRC_GIT_SERVERS
+- SYMBOLS_URL
+
+For detailed instructions on how to set these environment variables in a Docker Compose deployment, see the [Docker Compose configuration guide](/admin/deploy/docker-compose/configuration#set-environment-variables).