Controller for handling etcd storage for aggregated API servers
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README.md

etcdproxy-controller

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Implements https://groups.google.com/forum/#!msg/kubernetes-sig-api-machinery/rHEoQ8cgYwk/iglsNeBwCgAJ

Google Summer of Code

This project is result of my Google Summer of Code project: Storage API for Aggregated API Servers.

Project outline:

Kubernetes offers two ways to extend the core API, by using the CustomResourceDefinitons or by setting up an aggregated API server. This ensures users don’t need to modify the core API in order to add the features needed for their workflow, which later ensures the more stable and secure core API.

One missing part is how to efficiently store data used by aggregated API servers. This project implements a Storage API, with a main goal to share the cluster’s main etcd server with the Aggregated API Servers, allowing it to use cluster’s main etcd just like it would use it’s own etcd server.

Student: Marko Mudrinić
Mentors: David Eads, Dr. Stefan Schimanski

More details about the project, including links to proposals and progress tracker, can be found in the xmudrii/gsoc-2018-meta-k8s repository.

Purpose

This controller implements the EtcdStorage type, used to provide etcd storage for the aggregated API servers.

Compatibility

HEAD of this repo matches versions 1.10 of k8s.io/apiserver, k8s.io/apimachinery, and k8s.io/client-go.

Running controller

There are two ways to run EtcdProxyController:

Running the etcd cluster

Before running the controller, you need to expose an etcd cluster to the EtcdProxyController.

The EtcdProxyController assumes an etcd cluster is available on the https://etcd-svc-1.etcd.svc:2379 endpoint. The endpoint URL can be configured by modifying value of the --etcd-core-url flag in the 00-etcdproxy-controller.yaml manifest, or by providing the flag when running out-of-cluster.

There's an example manifest for deploying a single-node etcd cluster along with deploying instructions in the artifacts/etcd directory.

Deploying the EtcdProxyController in-cluster

To run the controller in-cluster, deploy the deployment manifest from the artifcats/deployment directory, using kubectl:

kubectl create -f artifacts/deployment/00-etcdproxy-controller.yaml

This manifest creates namespace for the EtcdProxyController, ServiceAccounts for controller and etcd-proxy pods, RBAC roles for managing all resources used by the controller, EtcdStorage CRD and EtcdProxyController Deployment.

The controller is deployed from the latest Docker Hub image, which can be found in the xmudrii/etcdproxy-controller Docker Hub repository.

More details about the deployment manifest can be found in the README file in the artifacts/deployment directory.

Running out-of-cluster

Running out-of-cluster is useful when developing the controller and you want to test the latest changes.

Before running the controller out-of-cluster you need to create the etcd proxy namespace and the EtcdStorage CRD.

The etcd proxy namespace is by default called kube-apiserver-storage (can be configured using --namespace flag), and we can create it using kubectl:

kubectl create namespace kube-apiserver-storage

The EtcdStorage CRD can be deployed using the manifest located in artifacts/etcdstorage directory:

kubectl create -f artifcats/etcdstorage/crd.yaml

To build the controller, you need the Go toolchain installed and configured.

You can build the controller using the compile Make target, which compiles the controller and creates a binary in the ./bin directory:

make compile

To run the controller, you need to provide it a path to kubeconfig and the URL of the core etcd:

./bin/etcdproxy-controller --kubeconfig ~/.kube/config --etcd-core-url https://etcd-svc-1.etcd.svc:2379

Providing the core etcd client certificates to the controller

Once the controller is deployed, before deploying the EtcdStorage resources, you need to provide the trust CA and client certificates for the core etcd to the EtcdProxyController, so etcd-proxy pods can access the etcd cluster.

The trust CA is provided by putting it in a ConfigMap in the controller (by default kube-apiserver-storage) namespace. The ConfigMap is by default called etcd-coreserving-ca, but can be configured using the --etcd-core-ca-configmap flag.

The client certificate/key pair is provided to the controller as TLS Secret in the controller namespace, where tls.crt is a client certificate and tls.key is a client key. The Secret is by default called etcd-coreserving-cert, but can be configured using the --etcd-core-ca-secret flag.

The ConfigMap and Secret can be created using the following kubectl commands:

kubectl create configmap etcd-coreserving-ca --from-file=ca.crt -n kube-apiserver-storage
kubectl create secret tls etcd-coreserving-cert --from-file=tls.crt --from-file=tls.key -n kube-apiserver-storage

When deploying the core etcd using the example manifest, you can deploy the trust CA and client certificate/key pair using the etcd-client-certs.yaml manifest. The README file in the artifacts/etcd directory contains more details about deploying the etcd and etcd client certificates.

Creating etcd instances for aggregated API servers

To create an etcd instance for your aggregated API server, you need to deploy an EtcdStorage resource.

The sample manifest is located in the artifacts/etcdstorage directory, and you can deploy it with kubectl, such as:

kubectl create -f artifacts/etcdstorage/example-etcdstorage.yaml

Once the EtcdStorage is deployed, the controller creates a Deployment for EtcdProxy pods, and a Service to expose the pods.

Then, you can use the etcd for your aggregated API server, over the URL such as http://etcd-<name-of-etcdstorage-object>.kube-apiserver-storage.svc:2379.

In case of the sample manifest, etcd is available on http://etcd-etcd-name.kube-apiserver-storage.svc:2379.

You can check what resources are created in the controller namespace with the following kubectl command:

kubectl get all -n kube-apiserver-storage

etcd-proxy certificates

The EtcdProxyController handles certificates generation, renewal and rotation for etcd-proxy.

When you create an EtcdStorage resource, the controller:

  • Creates client CA certificate and server certificate/key pair. Both are stored in the controller namespace and used by etcd-proxy pods.
  • Creates serving CA certificate and client certificate/key pair. Both are stored in the API server namespace and used by the API server.

The serving CA certificate is stored in a ConfigMap and the client certificate/key pair is stored in a Secret, both in API server namespace. The API server operator must create the ConfigMap and Secret, give the EtcdProxyController ServiceAccount the GET, UPDATE and PATCH permissions on the ConfigMap and Secret, and provide names of the ConfigMap and Secret in the EtcdStorage Spec, such as:

...
spec:
  caCertConfigMap:
  - name: etcd-serving-ca
    namespace: k8s-sample-apiserver
  clientCertSecret:
  - name: etcd-client-cert
    namespace: k8s-sample-apiserver
...

Beside providing destination ConfigMap and Secret, the API server operator have to provide the certificate validity for each certificate type: CA certificate, Serving certificate, and Client certificate.

This is done by setting appropriate keys in the EtcdStorage Spec:

spec:
  ...
  signingCertificateValidity: 730h # defines for how long the signing certificate is valid.
  servingCertificateValidity: 730h # defines for how long the serving certificate/key pair is valid.
  clientCertificateValidity:  730h # defines for how long the client certificate/key pair is valid.

It's recommended for value to be longer than 10 minutes.