Setting up Routing Rules using CRDs

Overview

Custom Resource Definitions (CRDs) are used to extend the Kubernetes APIs server with additional schemas. To know more, click here.

The Avi Kubernetes Operator (AKO) supports some CRD objects (installed through helm). The CRDs are relevant to:

Operators:
Users of this category:

  • Are aware of the Avi-related semantics
  • Have access to the Avi controller
  • Manage the lifecycle of AKO

Developers:
Users of this category:

  • Are owners of microservices deployed in Kubernetes
  • Are assumed to know basic routing principles but may not know the specifics of Avi attributes

Advantages of CRDs

Some load balancers allow configuration options via annotations.

The following are the advantages of using CRDs:

  • Versioning: CRDs allow AKO to version fields appropriately due to the dependency on the Avi Controller Versions. In general, this helps preserve unique states across various deployment versions.

  • Syntactical Validations: CRDs can be used to verify syntax at the time of creation of the CRD object. This saves API cost and facilitates quicker feedback using a combination of field constraints and effective status messages.

  • Role segregation: CRDs can benefit from the Role-based access control (RBAC) policies of Kubernetes and allow stricter access to a group of users.

Types of CRDs Supported in AKO

AKO categorizes the CRDs into:

  • Layer 7: These CRD objects are used to express layer 7 traffic routing rules.

  • Layer 4: These CRD objects are used to express layer 4 traffic routing rules.

  • Infrastructure: These CRD objects are used to control Avi’s infrastructure components like Ingress class, SE group properties etc.

Note: As of AKO release 1.1.1, only the layer 7 CRDs are supported.

Layer 7 CRDs

The following are the Layer 7 CRDs currently available in AKO:

HostRule

The HostRule CRD is used to express additional virtual host properties. The virtual host FQDN is matched from either the Kubernetes ingress or OpenShift route-based objects.

A sample HostRule CRD looks as shown below:


apiVersion: ako.vmware.com/v1alpha1
kind: HostRule
metadata:
   name: my-host-rule
   namespace: red
spec:
  virtualhost:
    fqdn: foo.com # mandatory
    tls: # optional
      sslKeyCertificate:
       name:"avi-ssl-key-cert"
       type: ref
      termination: edge
    httpPolicy: 
      policySets:
      - "my-secure-policy-ref"
      overwrite: false
    wafPolicy: "my-waf-policy"
    applicationProfile: "my-app-ref"

Usage of HostRule

HostRule CRD can be created in a given namespace where the operator requires better control. This section explains the details and associated rules of using each field of the HostRule CRD.

Express httppolicyset Object Refs

HostRule CRD can be used to express httppolicyset references.

Note: The httppolicyset objects should be pre-created in the Avi Controller.


     httpPolicy: 
       policySets:
       - "my-secure-policy-ref"
       overwrite: false

The httppolicyset currently is only applicable for secure FQDNs and cannot be applied for insecure routes. The order of evaluation of the httpolicyset rules is in the same order they appear in the CRD definition. The list of httpolicyset rules are always interpreted as an AND operation.

AKO currently uses the httppolicyset objects on the SNI virtual services to route traffic based on host/path matches. These rules are always at a lower index than the httppolicyset objects specified in the CRD object. In case, a user would want to overwrite all httppolicyset objects on a SNI virtual service with the ones specified in the HostRule CRD, the overwrite flag can be set to true.

Express WAF Policy Object Refs

HostRule CRD can be used to express WAF policy references.

Note: Create the WAF policy object in the Avi Controller prior to the CRD creation.

wafPolicy: "my-waf-policy"

This property can be applied only for secure FQDNs and cannot be applied for insecure routes. WAF policies are useful when deep layer 7 packet filtering is required.

Express Custom Application Profiles

HostRule CRD can be used to express application profile references.

Note: Create the application profile reference in the Avi Controller prior to the CRD creation. The application profile should be of Type APPLICATION_PROFILE_TYPE_HTTP.

applicationProfile: "my-app-ref"

This property can be applied only for secure FQDNs and cannot be applied for insecure routes. The application profiles can be used for various HTTP/HTTP2 protocol settings.

Express SSL Key and Certificates

For the Avi Kubernetes Operator to control the TLS termination from a privileged namespace, the HostRule CRD can be created in such a namespace.


    tls:
      sslKeyCertificate:
       name:"avi-ssl-key-cert"
       type: ref
      termination: edge

Here, Name refers to an Avi object of the type Ref.

Currently, edge is the only type of termination that is supported.

Status Messages

The status messages are used to give instant feedback about the reference objects specified in the HostRule CRD.

Following are some of the sample status messages:

Accepted HostRule Object


NAME                 HOST                  STATUS     AGE
secure-waf-policy    foo.avi.internal      Accepted   3d3h

A HostRule is accepted only when all the reference objects specified inside it exist in the Avi Controller.

A Rejected HostRule Object


 NAME                    HOST                  STATUS     AGE
secure-waf-policy-alt  foo.avi.internal       Rejected   2d23h

The reason for rejection can be obtained from the status:


status:
error: duplicate fqdn foo.avi.internal found in default/secure-waf-policy-alt
status: Rejected

Caveats

Converting Insecure FQDNs to Secure

The HostRule CRD can be used to convert an insecure host FQDN to a secure one. This is done by specifying a TLS section in the CRD object. The sslKeyCertificate is provided for the FQDN, will override all sslkeyandcertificates generated for the FQDN. This is useful if:

  • The operator wants to convert an insecure ingress FQDN to secure.

  • The operator wants to override any existing secrets for a given host FQDN and define TLS termination semantics.

HostRule Deletion

If a HostRule is deleted, all the settings for the FQDNs are withdrawn from the Avi controller.

HostRule Admission

A HostRule CRD is only admitted if all the objects referenced in it, exist in the Avi Controller. If after admission the object references are deleted out-of-band, then AKO does not re-validate the associated HostRule CRD objects. The user needs to manually edit or delete the object for new changes to take effect.

Duplicate FQDN rules

Two HostRule CRDs cannot be used for the same FQDN information across namespaces. If AKO finds a duplicate FQDN in more than one HostRules, AKO honors the first HostRule that gets created and rejects the others. In case of AKO reboots, the CRD that gets honored might not be the same as the one honored earlier.

HTTP Rule

The path matching rules in the ingress or route objects define traffic routing rules to the microservices. The HTTPRule CRD can be used as a complimentary object to control additional layer 7 properties like algorithm, hash, and tls re-encrypt use cases.

A sample HTTPRule object is as shown below:


apiVersion: ako.vmware.com/v1alpha1
kind: HTTPRule
metadata:
   name: my-http-rules
   namespace: purple-l7
spec:
  fqdn: foo.avi.internal
  paths:
  - target: /foo
    loadBalancerPolicy:
      algorithm: LB_ALGORITHM_CONSISTENT_HASH
      hash: LB_ALGORITHM_CONSISTENT_HASH_SOURCE_IP_ADDRESS
    tls: ## This is a re-encrypt to pool
      type: reencrypt # Mandatory [re-encrypt]
      sslProfile: "System-Default"

Note: The HTTPRule only applies to paths in the Ingress/Route objects which are specified in the same namespace as the HTTPRule CRD.

Usage of the HTTPRule CRD

The HTTPRule CRD does not have any Avi specific semantics. Hence you are free to express your preferences using this CRD without any knowledge of the Avi objects. Each HTTPRule CRD must be bound to a FQDN (both secure or insecure) to subscribe to rules for a specific hostpath combinations.

A HTTPRule CRD would be Rejected if the corresponding HostRule CRD does not exist.

Express Load Balancer Algorithm

The load balancer policies are a predefined set of values to choose from.
Currently, the following values are supported for load balancer policy:

  • LB_ALGORITHM_CONSISTENT_HASH
  • LB_ALGORITHM_CORE_AFFINITY
  • LB_ALGORITHM_FASTEST_RESPONSE
  • LB_ALGORITHM_FEWEST_SERVERS
  • LB_ALGORITHM_FEWEST_TASKS
  • LB_ALGORITHM_LEAST_CONNECTIONS
  • LB_ALGORITHM_LEAST_LOAD
  • LB_ALGORITHM_NEAREST_SERVER
  • LB_ALGORITHM_RANDOM
  • LB_ALGORITHM_ROUND_ROBIN
  • LB_ALGORITHM_TOPOLOGY

To configure the load balancer policy for a given ingress path, 


  target: /foo 
     loadBalancerPolicy:
       algorithm: LB_ALGORITHM_CONSISTENT_HASH

This rule is applied all paths matching /foo and subsets of /foo/xxx.

To know more, refer to the Load Balancing Algorithm article.

Reencrypt Traffic to the Services

While AKO can terminate TLS traffic, it also provides an option where the users can choose to re-encrypt the traffic between the Avi SE and the backend application server. The following option is provided for reencrypt:


    tls: ## This is a re-encrypt to pool
      type: reencrypt # Mandatory [re-encrypt]

If the sslProfile is not defined, AKO defaults to sslProfile System-Standard to exchange the tls parameters like TLS versions, ciphers etc.

As a further enhancement, you can specify a destination CA, that uses a PKI profile to validate the server certificates.

Status Messages

The status messages are used to give instant feedback on whether a HTTPRule CRD was accepted or rejected.

Example of a HTTP Rule


$ kubectl get httprule
NAME            HOSTRULE                     STATUS     AGE
my-http-rules   default/secure-waf-policy    Accepted   5h34m

Document Revision History

Date Change Summary
July 22, 2020 Published the article for Custom Resource Definitions