feat: add support for reverse proxy header handling

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## [Unreleased]
 
+### Added
+
+- Support for configuring which reverse proxies the webserver trusts `X-Forwarded-*` headers from, via `spec.webservers.roleConfig.trustedProxies` ([#835]).
+
 ### Changed
 
 - Internal operator refactoring: introduce a build() step in the reconciler that
@@ -32,6 +36,7 @@
 [#827]: https://github.com/stackabletech/airflow-operator/pull/827
 [#828]: https://github.com/stackabletech/airflow-operator/pull/828
 [#829]: https://github.com/stackabletech/airflow-operator/pull/829
+[#835]: https://github.com/stackabletech/airflow-operator/pull/835
 [#840]: https://github.com/stackabletech/airflow-operator/pull/840
 
 ## [26.7.0] - 2026-07-21

docs/modules/airflow/pages/usage-guide/reverse-proxy.adoc

@@ -0,0 +1,78 @@
+= Running behind a reverse proxy
+:description: Configure which reverse proxies the Airflow webserver trusts X-Forwarded-* headers from.
+
+When the Airflow webserver is reached through an ingress controller or another reverse proxy, every
+request arrives from the proxy rather than from the client. Unless the webserver is told to trust
+the proxy, it records the proxy's address as the client address, and it treats a TLS-terminated
+request as plain HTTP -- which, among other things, means session cookies are not marked as
+`Secure`.
+
+Set `trustedProxies` on the webserver role to the addresses your proxy sends requests from:
+
+[source,yaml]
+----
+spec:
+  webservers:
+    roleConfig:
+      listenerClass: external-stable
+      trustedProxies:
+        - 10.244.0.0/16 # <1>
+    roleGroups:
+      default:
+        replicas: 1
+----
+
+<1> IP addresses (`10.0.0.1`), CIDR networks (`10.244.0.0/16`), and `*` are accepted. `*` must be
+the only entry in the list: combining it with other entries is rejected, since it would silently
+degrade to trusting only those other entries.
+
+On Airflow 3.x the operator starts the api-server with `--proxy-headers` and restricts the headers
+to the listed peers. Airflow 2.x has no equivalent restriction: see
+<<airflow-2-x-has-no-peer-restriction>>.
+
+== Choosing the value
+
+Use the narrowest range that covers your proxy, and give it as a network address (host bits zero,
+e.g. `10.244.0.0/16`) or as a bare host IP (no `/prefix` at all, e.g. `10.244.0.5`).
+
+For an ingress controller running in the cluster, list the Pod addresses as bare host IPs rather
+than guessing a network:
+
+[source,bash]
+----
+kubectl get pods -n ingress-nginx -o jsonpath='{.items[*].status.podIP}'
+----
+
+If your ingress controller's Pods share a known, stable CIDR (for example a dedicated node pool or
+a documented Pod CIDR range for that namespace), you can use that network instead -- but confirm it
+against your cluster's actual CNI configuration rather than inferring it from a single Pod IP,
+since a Pod IP alone does not tell you where the network boundary is.
+
+`*` trusts forwarded headers from any peer that can reach the webserver. Only use it when access
+to the webserver is restricted by other means -- with a `cluster-internal` or
+`external-unstable` ListenerClass, clients reach the Pod directly and can set the headers
+themselves.
+
+WARNING: A peer that is trusted can set the client address that ends up in the webserver's access
+log. Do not list ranges wider than the proxies you operate.
+
+[#airflow-2-x-has-no-peer-restriction]
+== Airflow 2.x has no peer restriction
+
+Airflow 2.x's webserver has no analogue support for trusted network addresses. Once enabled, it
+unconditionally trusts `X-Forwarded-*` from *any* peer, the same as `trustedProxies: ["*"]` on 3.x.
+
+This means that for Airflow 2.x, `trustedProxies: ["*"]` is the only valid configuration. Using
+any other value than `*` will lead the operator to reject reconciliation.
+
+== Interaction with overrides
+
+On Airflow 3.x, the operator sets `FORWARDED_ALLOW_IPS` from this field, before `envOverrides` are
+applied -- so an `envOverrides` entry for that variable wins over the value derived from
+`trustedProxies`. This override only takes effect while `trustedProxies` is non-empty: an empty
+list means the api-server is not started with `--proxy-headers` at all, so uvicorn never installs
+the middleware that reads `FORWARDED_ALLOW_IPS`, and the override has no effect regardless of its
+value.
+
+On Airflow 2.x, the same applies to `AIRFLOW__WEBSERVER__ENABLE_PROXY_FIX` and
+`AIRFLOW__WEBSERVER__PROXY_FIX_X_FOR`.

docs/modules/airflow/partials/nav.adoc

@@ -8,6 +8,7 @@
 ** xref:airflow:usage-guide/mounting-dags.adoc[]
 ** xref:airflow:usage-guide/applying-custom-resources.adoc[]
 ** xref:airflow:usage-guide/listenerclass.adoc[]
+** xref:airflow:usage-guide/reverse-proxy.adoc[]
 ** xref:airflow:usage-guide/storage-resources.adoc[]
 ** xref:airflow:usage-guide/security.adoc[]
 ** xref:airflow:usage-guide/logging.adoc[]

extra/crds.yaml

@@ -5646,6 +5646,7 @@ spec:
                       podDisruptionBudget:
                         enabled: true
                         maxUnavailable: null
+                      trustedProxies: []
                     description: This is a product-agnostic RoleConfig, which is sufficient for most of the products.
                     properties:
                       listenerClass:
@@ -5686,6 +5687,24 @@ spec:
                             nullable: true
                             type: integer
                         type: object
+                      trustedProxies:
+                        default: []
+                        description: |-
+                          Enable trusted proxies when Airflow is deployed behind a reverse proxy like Istio or nginx.
+
+                          The reverse proxies whose `X-Forwarded-*` headers the webserver trusts, as IP addresses
+                          (`10.0.0.1`), CIDR networks (`10.244.0.0/16`), or `*` for every peer. `*` must be the
+                          only entry in the list if used: combining it with other entries is rejected, since it
+                          would silently degrade to trusting only those other entries.
+
+                          On Airflow 3.x this restricts trust to the listed peers. On 2.x it only switches
+                          forwarded-header handling on or off: any non-empty list trusts every peer, the same as
+                          `*`, since Airflow 2.x has no way to restrict it further.
+
+                          Leave this empty (the default) and forwarded headers are ignored entirely.
+                        items:
+                          type: string
+                        type: array
                     type: object
                   roleGroups:
                     additionalProperties:
@@ -11851,6 +11870,7 @@ spec:
                       podDisruptionBudget:
                         enabled: true
                         maxUnavailable: null
+                      trustedProxies: []
                     description: This is a product-agnostic RoleConfig, which is sufficient for most of the products.
                     properties:
                       listenerClass:
@@ -11891,6 +11911,24 @@ spec:
                             nullable: true
                             type: integer
                         type: object
+                      trustedProxies:
+                        default: []
+                        description: |-
+                          Enable trusted proxies when Airflow is deployed behind a reverse proxy like Istio or nginx.
+
+                          The reverse proxies whose `X-Forwarded-*` headers the webserver trusts, as IP addresses
+                          (`10.0.0.1`), CIDR networks (`10.244.0.0/16`), or `*` for every peer. `*` must be the
+                          only entry in the list if used: combining it with other entries is rejected, since it
+                          would silently degrade to trusting only those other entries.
+
+                          On Airflow 3.x this restricts trust to the listed peers. On 2.x it only switches
+                          forwarded-header handling on or off: any non-empty list trusts every peer, the same as
+                          `*`, since Airflow 2.x has no way to restrict it further.
+
+                          Leave this empty (the default) and forwarded headers are ignored entirely.
+                        items:
+                          type: string
+                        type: array
                     type: object
                   roleGroups:
                     additionalProperties: