Update READMEs (#3788)

Problem: The helm chart README contained a section that is outdated and removed from our official docs. Also, our main README contains some misleading language around supporting a subset of the Gateway API. While we technically do support a subset, the language makes it sound like our intention is to support a subset, which isn't really true and sounds worse than it is.

Solution: Remove the unneeded sections from both READMEs.

Author: sjberman

README.md

@@ -13,7 +13,7 @@ NGINX Gateway Fabric is an open-source project that provides an implementation o
 the [Gateway API](https://gateway-api.sigs.k8s.io/) using [NGINX](https://nginx.org/) as the data plane. The goal of
 this project is to implement the core Gateway APIs -- `Gateway`, `GatewayClass`, `HTTPRoute`, `GRPCRoute`, `TCPRoute`, `TLSRoute`,
 and `UDPRoute` -- to configure an HTTP or TCP/UDP load balancer, reverse-proxy, or API gateway for applications running
-on Kubernetes. NGINX Gateway Fabric supports a subset of the Gateway API.
+on Kubernetes.
 
 For a list of supported Gateway API resources and features, see
 the [Gateway API Compatibility](https://docs.nginx.com/nginx-gateway-fabric/overview/gateway-api-compatibility/) doc.

charts/nginx-gateway-fabric/README.md

@@ -20,7 +20,6 @@
     - [Upgrading the CRDs](#upgrading-the-crds)
     - [Upgrading the Chart from the OCI Registry](#upgrading-the-chart-from-the-oci-registry)
     - [Upgrading the Chart from the Sources](#upgrading-the-chart-from-the-sources)
-    - [Configure Delayed Termination for Zero Downtime Upgrades](#configure-delayed-termination-for-zero-downtime-upgrades)
   - [Uninstalling the Chart](#uninstalling-the-chart)
     - [Uninstalling the Gateway Resources](#uninstalling-the-gateway-resources)
   - [Configuration](#configuration)
@@ -117,15 +116,10 @@ helm install ngf oci://ghcr.io/nginx/charts/nginx-gateway-fabric --create-namesp
 
 ## Upgrading the Chart
 
-> [!NOTE]
->
-> See [below](#configure-delayed-termination-for-zero-downtime-upgrades) for instructions on how to configure delayed
-> termination if required for zero downtime upgrades in your environment.
-
 ### Upgrading the Gateway Resources
 
 Before you upgrade a release, ensure the Gateway API resources are the correct version as supported by the NGINX
-Gateway Fabric - [see the Technical Specifications](../../README.md#technical-specifications).:
+Gateway Fabric - [see the Technical Specifications](https://github.com/nginx/nginx-gateway-fabric/blob/main/README.md#technical-specifications).:
 
 To upgrade the Gateway CRDs from [the Gateway API repo](https://github.com/kubernetes-sigs/gateway-api), run:
 
@@ -168,57 +162,6 @@ the release `ngf`, run:
 helm upgrade ngf . -n nginx-gateway
 ```
 
-### Configure Delayed Termination for Zero Downtime Upgrades
-
-To achieve zero downtime upgrades (meaning clients will not see any interruption in traffic while a rolling upgrade is
-being performed on NGF), you may need to configure delayed termination on the NGF Pod, depending on your environment.
-
-> [!NOTE]
->
-> When proxying Websocket or any long-lived connections, NGINX will not terminate until that connection is closed
-> by either the client or the backend. This means that unless all those connections are closed by clients/backends
-> before or during an upgrade, NGINX will not terminate, which means Kubernetes will kill NGINX. As a result, the
-> clients will see the connections abruptly closed and thus experience downtime.
-
-1. Add `lifecycle` to both the nginx and the nginx-gateway container definition. To do so, update your `values.yaml`
-   file to include the following (update the `sleep` values to what is required in your environment):
-
-   ```yaml
-    nginxGateway:
-        <...>
-        lifecycle:
-            preStop:
-                exec:
-                    command:
-                    - /usr/bin/gateway
-                    - sleep
-                    - --duration=40s # This flag is optional, the default is 30s
-
-    nginx:
-        <...>
-        lifecycle:
-            preStop:
-                exec:
-                    command:
-                    - /bin/sleep
-                    - "40"
-   ```
-
-2. Ensure the `terminationGracePeriodSeconds` matches or exceeds the `sleep` value from the `preStopHook` (the default
-   is 30). This is to ensure Kubernetes does not terminate the Pod before the `preStopHook` is complete. To do so,
-   update your `values.yaml` file to include the following (update the value to what is required in your environment):
-
-   ```yaml
-   terminationGracePeriodSeconds: 50
-   ```
-
-> [!NOTE]
->
-> More information on container lifecycle hooks can be found in the official
-> [kubernetes documentation](https://kubernetes.io/docs/concepts/containers/container-lifecycle-hooks/#container-hooks) and a detailed
-> description of Pod termination behavior can be found in
-> [Termination of Pods](https://kubernetes.io/docs/concepts/workloads/Pods/Pod-lifecycle/#Pod-termination).
-
 ## Uninstalling the Chart
 
 To uninstall/delete the release `ngf`:

charts/nginx-gateway-fabric/README.md.gotmpl

@@ -19,7 +19,6 @@
     - [Upgrading the CRDs](#upgrading-the-crds)
     - [Upgrading the Chart from the OCI Registry](#upgrading-the-chart-from-the-oci-registry)
     - [Upgrading the Chart from the Sources](#upgrading-the-chart-from-the-sources)
-    - [Configure Delayed Termination for Zero Downtime Upgrades](#configure-delayed-termination-for-zero-downtime-upgrades)
   - [Uninstalling the Chart](#uninstalling-the-chart)
     - [Uninstalling the Gateway Resources](#uninstalling-the-gateway-resources)
   - [Configuration](#configuration)
@@ -115,15 +114,10 @@ helm install ngf oci://ghcr.io/nginx/charts/nginx-gateway-fabric --create-namesp
 
 ## Upgrading the Chart
 
-> [!NOTE]
->
-> See [below](#configure-delayed-termination-for-zero-downtime-upgrades) for instructions on how to configure delayed
-> termination if required for zero downtime upgrades in your environment.
-
 ### Upgrading the Gateway Resources
 
 Before you upgrade a release, ensure the Gateway API resources are the correct version as supported by the NGINX
-Gateway Fabric - [see the Technical Specifications](../../README.md#technical-specifications).:
+Gateway Fabric - [see the Technical Specifications](https://github.com/nginx/nginx-gateway-fabric/blob/main/README.md#technical-specifications).:
 
 To upgrade the Gateway CRDs from [the Gateway API repo](https://github.com/kubernetes-sigs/gateway-api), run:
 
@@ -166,57 +160,6 @@ the release `ngf`, run:
 helm upgrade ngf . -n nginx-gateway
 ```
 
-### Configure Delayed Termination for Zero Downtime Upgrades
-
-To achieve zero downtime upgrades (meaning clients will not see any interruption in traffic while a rolling upgrade is
-being performed on NGF), you may need to configure delayed termination on the NGF Pod, depending on your environment.
-
-> [!NOTE]
->
-> When proxying Websocket or any long-lived connections, NGINX will not terminate until that connection is closed
-> by either the client or the backend. This means that unless all those connections are closed by clients/backends
-> before or during an upgrade, NGINX will not terminate, which means Kubernetes will kill NGINX. As a result, the
-> clients will see the connections abruptly closed and thus experience downtime.
-
-1. Add `lifecycle` to both the nginx and the nginx-gateway container definition. To do so, update your `values.yaml`
-   file to include the following (update the `sleep` values to what is required in your environment):
-
-   ```yaml
-    nginxGateway:
-        <...>
-        lifecycle:
-            preStop:
-                exec:
-                    command:
-                    - /usr/bin/gateway
-                    - sleep
-                    - --duration=40s # This flag is optional, the default is 30s
-
-    nginx:
-        <...>
-        lifecycle:
-            preStop:
-                exec:
-                    command:
-                    - /bin/sleep
-                    - "40"
-   ```
-
-2. Ensure the `terminationGracePeriodSeconds` matches or exceeds the `sleep` value from the `preStopHook` (the default
-   is 30). This is to ensure Kubernetes does not terminate the Pod before the `preStopHook` is complete. To do so,
-   update your `values.yaml` file to include the following (update the value to what is required in your environment):
-
-   ```yaml
-   terminationGracePeriodSeconds: 50
-   ```
-
-> [!NOTE]
->
-> More information on container lifecycle hooks can be found in the official
-> [kubernetes documentation](https://kubernetes.io/docs/concepts/containers/container-lifecycle-hooks/#container-hooks) and a detailed
-> description of Pod termination behavior can be found in
-> [Termination of Pods](https://kubernetes.io/docs/concepts/workloads/Pods/Pod-lifecycle/#Pod-termination).
-
 ## Uninstalling the Chart
 
 To uninstall/delete the release `ngf`: