[GitHub] [apisix-ingress-controller] lingsamuel commented on issue #927: Proposal: support external name service

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lingsamuel commented on issue #927:
URL: https://github.com/apache/apisix-ingress-controller/issues/927#issuecomment-1206116262

   Hi, this is my proposal. Feel free to comment/review.
   
   ## Background
   The users' environment may be not a simple single K8s cluster, but may be multiple K8s clusters, a mix of K8s clusters and bare metal machines, or rely on third-party services. The current ApisixRoute does not support such complex environments.
   
   It would be a useful feature if ApisixRoute supports using ExternalName Service or domain name as a backend directly.
   
   ## Solution
   APISIX does support setting domain names or IP addresses as upstream nodes. We can extend our CRD to support this scenario.
   
   For external service, both the ExternalName service inside the K8s cluster and the third-party service outside the cluster will only have one node configured in the translated upstream `nodes` field, unlike the K8s service which may have several nodes.
   This allows multiple external services to be merged into a single upstream and gain healthCheck capabilities.
   
   ## Design
   We add a field named `upstream` to ApisixRoute, which has the same level as "backends". The user must fill in at least one of `upstream` or `backends`.
   The field `upstream` will refer to an ApisixUpstream CRD, where the external services are defined in the newly added field `externalNode`, indicating that the upstream node is pre-defined and does not need to resolve.
   An `externalNode` must have a `name` field pointing to the final node location, which can be a service name pointing to a k8s external name service, an IP address or a domain name. If it points to a k8s external name service, the `type` field should be `service`, or it should be the default value of `direct`. The node can also be configured with an optional load balancing weight, which defaults to 1.
   
   ```yaml
   apiVersion: apisix.apache.org/v2
   kind: ApisixRoute
   metadata:
     name: external-example
   spec:
     http:
     - name: example
       match:
         hosts:
         - external.example.com
         paths:
         - "/*"
       upstreams:
       - name: external-example # Refers to ApisixUpstream
         weight: 50
   ---
   apiVersion: apisix.apache.org/v2
   kind: ApisixUpstream
   metadata:
     name: external-example
   spec:
     externalNodes: # Indicates that this upstream doesn't need to resolve nodes
     - name: "httpbin.org"
       # could be "domain", "serivce"
       # if the value is `service`, the name must refers to a K8s ExternalName service
       type: domain
       weight: 1 # default value is 1
     healthCheck: # same as normal ApisixUpstream
       # ....
   ```
   
   ### Using upstream and backends together
   Users can use both `upstream` and `backend`. A route-level traffic-split plugin will be generated normally.
   Please note that since APISIX does not support health checks between multiple upstreams, we will only support health checks within the `upstream.nodes`.
   This means that the healthCheck section defined in ApisixUpstream is at the upstream level and its effect is limited to that upstream only, not at the Route level.


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