Kubernetes [1] aka K8s¶

A part of feature: Service Discovery [2]

Ocelot will call the K8s endpoints API in a given namespace to get all of the endpoints for a pod and then load balance across them. Ocelot used to use the services API to send requests to the K8s service but this was changed in PR 1134 because the service did not load balance as expected.

Install¶

The first thing you need to do is install the NuGet package that provides Kubernetes [1] support in Ocelot:

Install-Package Ocelot.Provider.Kubernetes

Then add the following to your ConfigureServices method:

services.AddOcelot().AddKubernetes();

If you have services deployed in Kubernetes, you will normally use the naming service to access them. Default usePodServiceAccount = true, which means that Service Account using Pod to access the service of the K8s cluster needs to be Service Account based on RBAC authorization:

public static class OcelotBuilderExtensions
{
    public static IOcelotBuilder AddKubernetes(this IOcelotBuilder builder, bool usePodServiceAccount = true);
}

You can replicate a Permissive using RBAC role bindings (see Permissive RBAC Permissions), K8s API server and token will read from pod.

kubectl create clusterrolebinding permissive-binding --clusterrole=cluster-admin --user=admin --user=kubelet --group=system:serviceaccounts

Configuration¶

The following examples show how to set up a Route that will work in Kubernetes. The most important thing is the ServiceName which is made up of the Kubernetes service name. We also need to set up the ServiceDiscoveryProvider in GlobalConfiguration.

Kube default provider¶

The example here shows a typical configuration:

"Routes": [
  {
    "ServiceName": "downstreamservice",
    // ...
  }
],
"GlobalConfiguration": {
  "ServiceDiscoveryProvider": {
    "Host": "192.168.0.13",
    "Port": 443,
    "Token": "txpc696iUhbVoudg164r93CxDTrKRVWG",
    "Namespace": "Dev",
    "Type": "Kube"
  }
}

Service deployment in Namespace Dev, ServiceDiscoveryProvider type is Kube, you also can set PollKube provider type.

Note 1: Host, Port and Token are no longer in use.

Note 2: The Kube provider searches for the service entry using ServiceName and then retrieves the first available port from the EndpointSubsetV1.Ports collection. Therefore, if the port name is not specified, the default downstream scheme will be http;

PollKube provider¶

You use Ocelot to poll Kubernetes for latest service information rather than per request. If you want to poll Kubernetes for the latest services rather than per request (default behaviour) then you need to set the following configuration:

"ServiceDiscoveryProvider": {
  "Namespace": "dev",
  "Type": "PollKube",
  "PollingInterval": 100 // ms
}

The polling interval is in milliseconds and tells Ocelot how often to call Kubernetes for changes in service configuration.

Please note, there are tradeoffs here. If you poll Kubernetes, it is possible Ocelot will not know if a service is down depending on your polling interval and you might get more errors than if you get the latest services per request. This really depends on how volatile your services are. We doubt it will matter for most people and polling may give a tiny performance improvement over calling Kubernetes per request. There is no way for Ocelot to work these out for you.

Global vs Route Levels¶

If your downstream service resides in a different namespace, you can override the global setting at the Route-level by specifying a ServiceNamespace:

"Routes": [
  {
    "ServiceName": "downstreamservice",
    "ServiceNamespace": "downstream-namespace"
  }
]

Downstream Scheme vs Port Names [3]¶

Kubernetes configuration permits the definition of multiple ports with names for each address of an endpoint subset. When binding multiple ports, you assign a name to each subset port. To allow the Kube provider to recognize the desired port by its name, you need to specify the DownstreamScheme with the port’s name; if not, the collection’s first port entry will be chosen by default.

For instance, consider a service on Kubernetes that exposes two ports: https for 443 and http for 80, as follows:

Name:         my-service
Namespace:    default
Subsets:
  Addresses:  10.1.161.59
  Ports:
    Name   Port  Protocol
    ----   ----  --------
    https  443   TCP
    http   80    TCP

When you need to use the http port while intentionally bypassing the default https port (first one), you must define DownstreamScheme to enable the provider to recognize the desired http port by comparing DownstreamScheme with the port name as follows:

"Routes": [
  {
    "ServiceName": "my-service",
    "DownstreamScheme": "http", // port name -> http -> port is 80
  }
]

Note: In the absence of a specified DownstreamScheme (which is the default behavior), the Kube provider will select the first available port from the EndpointSubsetV1.Ports collection. Consequently, if the port name is not designated, the default downstream scheme utilized will be http.