add documentation for terraform overrides

docs/source/installation/configuration.md

@@ -690,6 +690,36 @@ jupyterhub:
       users: true
 ```
 
+## Terraform Overrides
+
+The QHub configuration file provides a huge number of configuration options for customizing your
+QHub Infrastructure, while these options are sufficient for an average user, but aren't
+exhaustive by any means. There are still a plenty of things you might want to achieve which
+cannot be configured directly by the above mentioned options, hence we have introduced a
+new option called terraform overrides (`terraform_overrides`), which lets you override
+the values of terraform variables in specific modules/resource. This is a relatively
+advance feature and must be used with utmost care and you should really know, what
+you're doing.
+
+Here we describe the overrides supported via QHub config file:
+
+### Ingress
+
+You can configure the IP of the load balancer and add annotations for the same via `ingress`'s
+terraform overrides, one such example for GCP is:
+
+
+```yaml
+ingress:
+  terraform_overrides:
+      load_balancer_annotations:
+          "networking.gke.io/load-balancer-type": "Internal"
+          "networking.gke.io/internal-load-balancer-subnet": "pre-existing-subnet"
+      load_balancer_ip: "1.2.3.4"
+```
+
+This is quite useful for pinning the IP Address of the load balancer.
+
 # Full configuration example
 
 ```yaml

qhub/schema.py

@@ -464,7 +464,7 @@ class Main(Base):
     prevent_deploy: bool = (
         False  # Optional, but will be given default value if not present
     )
-    ingress: Ingress
+    ingress: typing.Optional[Ingress]
 
     # If the qhub_version in the schema is old
     # we must tell the user to first run qhub upgrade

qhub/stages/input_vars.py

@@ -150,7 +150,9 @@ def stage_04_kubernetes_ingress(stage_outputs, config):
         "acme-email": config["certificate"].get("acme_email"),
         "acme-server": config["certificate"].get("acme_server"),
         "certificate-secret-name": config["certificate"]["secret_name"],
-        "load-balancer-annotations": config["ingress"]["terraform_overrides"]["load_balancer_annotations"],
+        "load-balancer-annotations": config["ingress"]["terraform_overrides"][
+            "load_balancer_annotations"
+        ],
         "load-balancer-ip": config["ingress"]["terraform_overrides"]["load-balancer-ip"]
         if config["certificate"]["type"] == "existing"
         else None,