Resource validation
Overview
This document describes how NGINX Gateway Fabric validates Gateway API and NGINX Gateway Fabric Kubernetes resources.
Gateway API resource validation
NGINX Gateway Fabric validates Gateway API resources for several reasons:
- Robustness: to gracefully handle invalid resources.
- Security: to prevent malicious input from propagating to the NGINX configuration.
- Correctness: to conform to the Gateway API specification for handling invalid resources.
The process involves four different steps, explained in detail in this document, with the goal of making sure that NGINX continues to handle traffic even if invalid Gateway API resources were created.
Step 1 - OpenAPI Scheme validation by Kubernetes API Server
The Kubernetes API server validates Gateway API resources against the OpenAPI schema embedded in the Gateway API CRDs. For example, if you create an HTTPRoute with an invalid hostname “cafe.!@#$%example.com”, the API server will reject it with the following error:
kubectl apply -f coffee-route.yaml
The HTTPRoute "coffee" is invalid: spec.hostnames[0]: Invalid value: "cafe.!@#$%example.com": spec.hostnames[0] in body should match '^(\*\.)?[a-z0-9]([-a-z0-9]*[a-z0-9])?(\.[a-z0-9]([-a-z0-9]*[a-z0-9])?)*$'
Note:
While unlikely, bypassing this validation step is possible if the Gateway API CRDs are modified to remove the validation. If this happens, Step 4 will reject any invalid values (from NGINX perspective).
Step 2 - CEL validation by Kubernetes API Server
The Kubernetes API server validates Gateway API resources using CEL validation embedded in the Gateway API CRDs. It validates Gateway API resources using advanced rules unavailable in the OpenAPI schema validation. For example, if you create a Gateway resource with a TCP listener that configures a hostname, the CEL validation will reject it with the following error:
kubectl apply -f some-gateway.yaml
The Gateway "some-gateway" is invalid: spec.listeners: Invalid value: "array": hostname must not be specified for protocols ['TCP', 'UDP']
More information on CEL in Kubernetes can be found here.
Step 3 - Validation by NGINX Gateway Fabric
This step catches the following cases of invalid values:
- Valid values from the Gateway API perspective but not supported by NGINX Gateway Fabric yet. For example, a feature in an HTTPRoute routing rule. For the list of supported features see Gateway API Compatibility doc.
- Valid values from the Gateway API perspective, but invalid for NGINX, because NGINX has stricter validation requirements for certain fields. These values will cause NGINX to fail to reload or operate erroneously.
- Invalid values (both from the Gateway API and NGINX perspectives) that were not rejected because Step 1 was bypassed. Similar to the previous case, these values will cause NGINX to fail to reload or operate erroneously.
- Malicious values that inject unrestricted NGINX config into the NGINX configuration (similar to an SQL injection attack).
Below is an example of how NGINX Gateway Fabric rejects an invalid resource. The validation error is reported via the status:
kubectl describe httproutes.gateway.networking.k8s.io coffee
. . .
Status:
Parents:
Conditions:
Last Transition Time: 2023-03-30T22:37:53Z
Message: All rules are invalid: spec.rules[0].matches[0].method: Unsupported value: "CONNECT": supported values: "DELETE", "GET", "HEAD", "OPTIONS", "PATCH", "POST", "PUT"
Observed Generation: 1
Reason: UnsupportedValue
Status: False
Type: Accepted
Controller Name: gateway.nginx.org/nginx-gateway-controller
Parent Ref:
Group: gateway.networking.k8s.io
Kind: Gateway
Name: prod-gateway
Namespace: default
Section Name: http
Note:
This validation step always runs and cannot be bypassed.
Confirm validation
To confirm that a resource is valid and accepted by NGINX Gateway Fabric, check that the Accepted condition in the resource status has the Status field set to True. For example, in a status of a valid HTTPRoute, if NGINX Gateway Fabric accepts a parentRef, the status of that parentRef will look like this:
Status:
Parents:
Conditions:
Last Transition Time: 2023-03-30T23:18:00Z
Message: The route is accepted
Observed Generation: 2
Reason: Accepted
Status: True
Type: Accepted
Controller Name: gateway.nginx.org/nginx-gateway-controller
Parent Ref:
Group: gateway.networking.k8s.io
Kind: Gateway
Name: gateway
Namespace: default
Section Name: http
Note:
Make sure the reported observed generation is the same as the resource generation.
NGINX Gateway Fabric Resource validation
Step 1 - OpenAPI Scheme validation by Kubernetes API Server
The Kubernetes API server validates NGINX Gateway Fabric resources against the OpenAPI schema embedded in the NGINX Gateway Fabric CRDs. For example, if you create an NginxGateway with an invalid logging level, “some-level”, the API server will reject it with the following error:
kubectl apply -f nginx-gateway-config.yaml
The NginxGateway "nginx-gateway-config" is invalid: spec.logging.level: Unsupported value: "some-level": supported values: "info", "debug", "error"
Note:
While unlikely, bypassing this validation step is possible if the NGINX Gateway Fabric CRDs are modified to remove the validation. If this happens, Step 2 will report an error in the resource’s status.
Step 2 - Validation by NGINX Gateway Fabric
This step validates the settings in the NGINX Gateway Fabric CRDs and rejects invalid resources. The validation error is reported via the status and as an Event. For example:
kubectl describe nginxgateways.gateway.nginx.org nginx-gateway-config
Status:
...
Status:
Conditions:
Last Transition Time: 2023-12-15T21:02:30Z
Message: Failed to update control plane configuration: logging.level: Unsupported value: "some-level": supported values: "info", "debug", "error"
Observed Generation: 1
Reason: Invalid
Status: False
Type: Valid
Event:
Warning UpdateFailed 1s (x2 over 1s) nginx-gateway-fabric-nginx Failed to update control plane configuration: logging.level: Unsupported value: "some-level": supported values: "info", "debug", "error"
Confirm validation
To confirm that a resource is valid and accepted by NGINX Gateway Fabric, check that the Valid condition in the resource status has the Status field set to True. For example, the status of a valid NginxGateway will look like this:
Status:
Conditions:
Last Transition Time: 2023-12-15T21:04:49Z
Message: NginxGateway is valid
Observed Generation: 1
Reason: Valid
Status: True
Type: Valid